2017 Eclipse: DIY Test Report: MEADES The Great Eclipse of 1878:

RELATIVITY TEST p. 32 MEGA-WIDE EYEPIECES p. 58 VULCANS LAST STAND p. 36

T H E E S S E N T I A L G U I D E TO A S T R O N O M Y

Whisky Prize:
The Million-Star Solution p. 16
One-Stop Processing
with PixInsight p. 66

AUGUST 2016

HOW TO EXPLORE
PLANETARY NEBULAE:

An Observing
Challenge p. 22

Perseids to Get a Boost? p. 48

Explore the Moon:
Hidden Lunar Basin p. 52
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 August 2016 VOL. 132, NO. 2

On the cover: O B S E RV I N G AU G U S T
This illustration 41 In This Section
depicts the Twin Jet
Nebula, created by a 42 Augusts Sky at a Glance
dying star in a binary
system thats expel- 43 Binocular Highlight
ling its outer layers By Mathew Wedel
of dusty gas.
ILLUSTRATION: CASEY REED
44 Planetary Almanac

45 Northern Hemispheres Sky

By Fred Schaaf
F E AT U R E S

16 A Million Stars 46 Sun, Moon & Planets

Crashing code, unasked-for black holes, By Fred Schaaf
and months of work lost to mistakes
48 Celestial Calendar
astrophysicists battled many foes in their By Alan MacRobert
quest to create the Holy Grail of star
cluster simulations. By Benjamin Skuse 52 Exploring the Moon xx

DAVE YOUNG / CC BY 2.0

By Charles A. Wood
22 Meet the Minkowskis
54 Deep-Sky Wonders
COVER
STORY
The Minkowski catalog of planetary
nebulae will keep you at the eyepiece
By Sue French 28
for years to come. By Ted Forte S &T T E S T R E P O R T
58 Meades MWA Eyepieces Theres more to find online @
28 Visual Filters for By Rod Mollise
Deep-Sky Observing SkyandTelescope.com
While not a magic bullet for defeating ALSO IN THIS ISSUE
light pollution, nebula lters are still a 4 Spectrum
boon for many urban observers. By Peter Tyson ASTRONOMY EVENTS
By Rod Mollise Check out our events calendar
6 Letters
for upcoming museum exhibits,
32 A Do-It-Yourself Relativity Test 8 75, 50 & 25 Years Ago star parties, and more or add
Using o-the-shelf equipment during By Roger W. Sinnott your own event to our listings!
next years total solar eclipse, you can SkyandTelescope.com/
prove that Einstein really was right. 10 News Notes astronomy-events
By Donald Bruns
62 New Product Showcase
ONLINE STORE
36 The Great American Eclipse 64 Astronomers Workbench Shop our online store for globes,
of the 19th Century By Jerry Oltion sky atlases, books, and more.
In the summer of 1878, astronomers and ShopatSky.com
tourists were newly ready to swarm into 72 Book Review
the Wild West. By William Sheehan By S. N. Johnson-Roehr
TIPS FOR BEGINNERS
73 Gallery New to astronomy? Heres
66 Processing with PixInsight
everything you need to jump
Follow this workow to get more out of 84 Focal Point into the fun.
your deep-sky astrophotos. By Rod Mollise
SkyandTelescope.com/letsgo
By Ron Brecher
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2 August 2016 sky & telescope

 The Sky-Watcher USA Star Adventurer multi-purpose mount is perfect for
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 August 2016 Digital Extra
B ON US CHE CK O UT
WE B CONTE NT Photo Gallery O UR B LO GS!
Watch Globular Explore the Night
Clusters Evolve From the newest nova to
The whisky-winning sim- overlooked wonders, follow
ulations are showcased in Bob King as he investigates
this interactive gallery. the mysteries awaiting us
in the night sky.
Planetary Nebulae Astronomy in Space
Up for an observing
challenge? Explore the David Dickinson keeps up
Minkowski catalog. Image by with the latest launches,
Sergio Emilio Montfar Codoer mission proposals, and more.
More from Stargazers Corner
1001 Celestial Wonders S&Ts Hear from our readers as
Read C.E. Barnss colorful
and evocative descriptions
Celestial they describe astro-

of deep-sky sights. Globe adventures and offer

observing advice.
Enjoy a state-of-
NEW
the-art representation
TOUR THE SKY of the entire night sky
on a 12-inch sphere.
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August 2016 sky & telescope

ONLINE PH OTO GALLE RY
Ezequiel Etcheverry captured this shot of
the Pelican and North American Nebulae.
Peter Tyson
Spectrum
Founded in 1941
by Charles A. Federer, Jr.
and Helen Spence Federer

The Essential Guide

to Astronomy

Taking Up the Gauntlet EDITORIAL

Editor in Chief Peter Tyson
Senior Editors J. Kelly Beatty, Alan M. MacRobert
Equipment Editor Sean Walker
Science Editor Camille M. Carlisle
Amateur astronomers love a challenge. That was in full Web Editor Monica Young
Observing Editor S. N. Johnson-Roehr
evidence on the two clear nights I had the pleasure of attending early Mays
Texas Star Party, in the ultra-dark Davis Mountains of West Texas. Senior Contributing Editors Robert Naeye, Roger W. Sinnott

The TSP organizers had a mission ready for observers at every level. The Contributing Editors Howard Banich, Jim Bell, Trudy Bell, John E. Bortle,
Fort Bend Astronomy Club crafted a naked-eye list for beginners. The Texas Greg Bryant, Thomas A. Dobbins, Alan Dyer, Tom Field, Tony Flanders,
Ted Forte, Sue French, Steve Gottlieb, David Grinspoon, Ken Hewitt-
Astronomical Society of Dallas put together three binocular lineups: one for White, Johnny Horne, Bob King, Emily Lakdawalla, Jerry Lodriguss,
small- to medium-aperture binocs, another for 50 mm or larger, and the third Rod Mollise, Donald W. Olson, Jerry Oltion, Joe Rao, Dean Regas, Fred
well, that was the Binocular Program from Hell. For telescope users, the Schaaf, Govert Schilling, William Sheehan, Mike Simmons, Mathew
Wedel, Alan Whitman, Charles A. Wood, Robert Zimmerman
Columbus Astronomical Society oered a
sampling entitled Spiralmania, with 22 of Contributing Photographers P. K. Chen, Akira Fujii, Robert Gendler,
Ted Sakers favorite spiral galaxies. Babak Tafreshi

Then there was Larry Mitchells ART & DESIGN

advanced telescopic list or should I say Design Director Patricia Gillis-Coppola
S&T: PETER TYSON

tome. Mitchell, of the Houston Astronomi- Illustration Director Gregg Dinderman

Illustrator Leah Tiscione
cal Society, had assembled a compendium
of nder charts and background informa- ADVERTISING

Larry Mitchell with his 36-inch Dob

tion 50 pages long. His 44 objects bore Advertising Sales Director Peter D. Hardy, Jr.
Digital Ad Services Manager Lester J. Stockman
names leading with Arakelian, Kazarian,
or Shakhbazian. These targets, roughly as dicult as the Minkowski plan- F + W, A C O N T E N T + E C O M M E R C E C O M P A N Y

etary nebulae we feature on page 22, are distant galaxies or galaxy clusters CEO Thomas F. X. Beusse
CFO / COO James L. Ogle
discovered in the last century by Armenian astronomers at the Byurakan
VP / Group Publisher Phil Sexton
Astrophysical Observatory. Senior VP / Operations Phil Graham
Each night, all three observing elds at Prude Ranch hummed like VP Communications Stacie Berger
beehives. Here were two women leaning over a chart-spread table bathed in Editorial Correspondence (including permissions, partnerships, and
red light, one helping her novice friend with the naked-eye tally. Over there content licensing): Sky & Telescope, 90 Sherman St., Cambridge, MA 02140-
was a man rigging up a brand-new 14-inch PlaneWave CDK14 Corrected 3264, USA. Phone: 617-864-7360. E-mail: editors@SkyandTelescope.com.
Website: SkyandTelescope.com. Unsolicited proposals, manuscripts, photo-
Dall-Kirkham telescope. Nearby was a knot of amateurs known as the Shade graphs, and electronic images are welcome, but a stamped, self-addressed
Tree Gang. Its members clustered near the eponymous tree like honeybees envelope must be provided to guarantee their return; see our guidelines for
doing the waggle dance, oering one another tips on how to locate the best contributors at SkyandTelescope.com.
nectar: a dicult object from one of the lists. Advertising Information: Peter D. Hardy, Jr., 617-864-7360, ext. 22133.
The one person who seemed utterly relaxed and somehow outside the Fax: 617-864-6117. E-mail: peterh@SkyandTelescope.com
buzz of activity was Mitchell himself. He passed the time, at least during the Web: SkyandTelescope.com/advertising

few instances I stopped by to chat with him, swinging his 36-inch Dobso- Customer Service: Magazine customer service and change-of-address
nian around to miscellaneous awe-inspiring destinations. Anyone willing to notices: skyandtelescope@emailcustomerservice.com
Phone toll free U.S. and Canada: 800-253-0245.
climb Mitchells towering, three-legged ladder was welcome to have a look. Outside the U.S. and Canada: 386-597-4387.
I did so many times. Through that magnicent instrument, M51 looked
Visit ShopatSky.com
as youve always thought a galaxy should: like a ghostly Hubble image. The Your source for the best astronomy resources available
wafer-thin, edge-on galaxy NGC 5907 displayed its slender dust lane impres- ShopatSky.com customer service: skyprodservice@SkyandTelescope.com
sively. In the Clown-face Nebula, I could readily see the familiar inner ring 888-253-0230.
tinged slightly blue, with the dimmer outer ring bearing a hint of red. Subscription Rates: U.S. and possessions: $42.95 per year (12 issues);
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Challenges met. Newsstand and Retail Distribution:

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Editor in Chief

4 August 2016 sky & telescope

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 Letters

George Carruthers Lunar Scope Contrary to Jim Bells opinion (S&T:

As a follow-up to Frank Ridolfos reminder June 2016, p. 84), I certainly hope it is
that weve had a telescope on the Moon not inevitable that we send humans to
since the early 1970s (S&T: Apr. 2016, p. 6), Mars. Perhaps such missions will become
let me extol its builder: George R. Car- technically feasible within the near future,
ruthers, then at the U.S. Naval Research but would they be the best use of our
Laboratory in Washington, D.C. resources and the wisest focus of our
Carruthers dedicated himself not only aspirations, ingenuity, and collective will?
to such astronomical ventures but also to Almost all of the payload of a human
stimulating interest in science and tech- Mars mission would need to be devoted
nology among young African Americans. to life support, and, at least initially, the
An early supporter of Project SMART crews would need to return to Earth.
(Science, Mathematics, Aerospace, With the same investment of money and
Research, and Technology) in the District human capital, how many robots could
of Columbia, he once told me during we send to Mars and leave there perma-
an interview that the overall objective nently? As space-faring machines become
of SMART is to get African Americans ever more sophisticated and autonomous,
involved in science and technology what scientic purpose would justify the
U.S. NAVAL RESEARCH LABORATORY

careers and also to become technologi- George Carruthers (at right) stands tremendously greater expense and risk of
cally literate, even if they dont choose with the gold-plated ultraviolet camera/ sending human astronauts to Mars?
careers in science and technology. spectrograph that he invented and which I fear the romantic frontier fantasy
Among his many mentoring ventures, Apollo 16 astronauts placed on the Moon of colonizing other planets could seduce
Carruthers brought local students to his in April 1972. Project engineer William us into ignoring the urgent problems of
NRL laboratory. One of their projects Conway is at left. climate disruption, species extinction,
in the 1990s was to restore the backup and environmental devastation we have
engineering model of Apollo 16s far- support with our passion for space travel created here on Earth. Preserving this
ultraviolet telescope/camera. Wed had it (S&T: May 2016, p. 16). I too grumble about planet is the best possible focus of a global
in our collection for a decade and wanted the budget for the International Space Sta- initiative that draws on the best we all
to bring it up to display-worthy condition. tion compared with those for all our robot have to oer.
Carruthers and his students obliged probes, which send back so much data at So, by all means, lets explore the uni-
even adding one of the lm cassettes that much less risk and lower cost. verse with telescopes and robots!
the Apollo 16 crew had brought back to But theres change in the air more Anthony Barreiro
Earth. Their eort has been on display private spacecraft are going up, and high- San Francisco, California
ever since at the National Air and Space rollers are even contemplating tiny probes
Museum in Washington, D.C., where that could be sent all the way to the star Finding Peace in the Stars
visitors from all walks of life can view it closest to ours [see page 11]. Somehow, After reading Peter Tysons recent Spec-
and appreciate its origins. some way, we are going to link up with trum, Escape to the Stars (S&T: Mar.
David DeVorkin possible life in our solar system and then 2016, p. 4), I recalled the following words
Division of Space History to the nearest stars. of Pavel Florensky, a Russian Orthodox
National Air and Space Museum Im 76 now, and I hope to live long priest, philosopher, and mathemati-
Smithsonian Institution enough to share in such news. Then all cian executed in 1937 after several years
Ill need will be my Chicago Cubs win- of imprisonment in a Soviet gulag. He
Funding Human Space Travel ning their rst World Series since 1908. wrote this in one of the last letters to his
Once again, David Grinspoon contrasts Earl Finkler children: Look more often at the stars.
hard science and shrinking government Medford, Wisconsin When you have a weight on your soul,
look at the stars or the blue of the sky.
When you feel sad, when they oend you
Write to Letters to the Editor, Sky & Telescope, 90 Sherman St., Cambridge, MA 02140-3264, or send stop yourselves . . . with the heavens.
e-mail to letters@SkyandTelescope.com. Please limit your comments to 250 words. Published letters may Then your soul will nd peace.
be edited for clarity and brevity. Due to the volume of mail, not all letters can receive personal responses. Alessandro Maitan
Forl, Italy

6 August 2016 sky & telescope

 iii

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 Letters

In Praise of Star Parties Astronomy Expo. Not one word for a However, he missed an important
Thank you for Rod Mollises very impor- gathering thats been going on for nigh aspect of the star-party scene: the now-
tant article on the importance, fun, and on a half century and for which Sky & ubiquitous use of green laser pointers.
excitement of star parties (S&T: Apr. 2016, Telescope is a consistent (and much appre- I realize that these are not welcome at
p. 34). To his list of major U.S. events, ciated) supporter. May I assume thats gatherings at which fellow stargazers
wed like to add one that celebrates its because youre devoting an entire article are taking astrophotographs. However,
30th anniversary this summer: the Rocky to RTMC? what about at small informal gatherings?
Mountain Star Stare (RMSS). Located on Fred Veretto And how might the use of these devices
land owned by the Colorado Springs Astro- San Marcos, California be restricted in the future? Green laser
nomical Society, RMSS takes place under pointers have certainly become a welcome
some of the darkest skies in the U.S. With Kelly Beatty replies: The legendary Riverside (necessary?) tool for the amateur astrono-
more than 300 attendees (the largest star Telescope Makers Conference ranks high on mer. I, for one, hope they remain avail-
party in Colorado), RMSS draws visitors Rod Mollises star-party bucket list. While able and acceptable.
from across the country and oers great his article focused on star parties designed Bert Probst
guest lectures. We invite our fellow S&T primarily for observing under very dark Ellicottville, New York
readers to check out rmss.org and to con- skies, RTMC is denitely included in the
sider attending this years event from June more exhaustive listing of annual events For the Record
29th to July 4th. (http://is.gd/star_parties) maintained on In the plot of our eyes response to lumi-
Bruce Bookout and Hal Bidlack SkyandTelescope.com. nance (S&T: June 2016, p. 24), the value 0
Colorado Springs, Colorado along the x-axis should be 1.
Mollises insightful view of future star Due to a production error, the evening-sky
I was surprised and disappointed at Rod parties was a joy to read and, I feel, an illustration for June 1214 appears twice
Mollises lack of mention of the RTMC accurate guide to where theyre headed. (S&T: June 2016, p. 46).

75, 50 & 25 Years Ago Roger W. Sinnott

August 1941 upper atmosphere, on August 1991
The League is Born the fringe of space. . . . Resolving Stars Disks
The Washington This is operation The astronomers
convention of amateur HARP, the letters stand- impossible dream has
astronomers is now ing for High Altitude always been to resolve
past. . . . Soon there Research Project, an features on the disks
ought to be an invitation experimental program of stars. Optically it
to hold it on the West being conducted by cant be done, [but]
Coast. . . . This would McGill University of an ingenious trick can
help toward establishing [a] national organiza- Montreal, Canada, and the U. S. Army Materiel sometimes accomplish the impossible. The
tion of amateur societies, since representa- Command. Brainchild of Prof. G. V. Bull at technique of Doppler imaging can map the
tion of all regions is of great importance. And McGill, HARP is a means of lifting research surface of a rotating body that has bright and
the proposed constitution of the Amateur loads into the upper atmosphere. . . . A disad- dark regions as seen at a narrow wavelength.
Astronomers League of America, as revised by vantage is that all experiments in the vehicle Radar astronomers have used this method to
the Washington convention, comes close to must be engineered to withstand accelerations map planets, especially Venus. Now it is being
making such [an] organization possible of some 25,000 g (gravity). applied to stars of type Ap, where intense mag-
and permanent. As meteor astronomer Peter Millman noted, netic elds segregate chemical elements into
Through their editorials and personal con- the HARP launcher utilized two U.S. Navy dierent areas on the stellar surface. . . .
tacts, S&T founders Charles and Helen Federer battleship gun barrels welded end to end. It had Artie P. Hatzes (University of Texas) cre-
vigorously supported what has become todays many rings in the 1960s, during which night- ated [global maps of the highly magnetized
Astronomical League. time chemical releases yielded valuable data star Theta Aurigae] by analyzing the changing
on wind shear at altitudes up to 130 kilometers absorption-line proles of singly ionized silicon
August 1966 (81 miles). Thereafter Gerald Bulls career took a and chromium.
Big Gun Barbados is a coral island 18 miles dark turn. In the 1980s he sold Saddam Hussein A more powerful technique has since
long by some 14 miles wide. [There] we nd the on the idea of a supergun, dubbed Big Babylon, emerged: interferometric imaging in visible light.
largest gun in the world, 119 feet of 16-inch cali- with which Iraq could target the capitols of both The University of Georgias CHARA Array, set up
ber barrel. . . . But the island is not expecting Israel and Iran. In March 1990 Bull was mysteri- at Mount Wilson Observatory, uses six 1-meter
an attack from the direction of South America, ously assassinated in Belgium, and a few months mirrors on a Y-shaped track. It can measure stel-
for this gun is just one more piece of equip- later the First Gulf War curtailed Husseins plans lar sizes and resolve ares and starspots as small
ment in mans eort to understand the earths for a supergun. as 0.0002 arcsecond.

8 August 2016 sky & telescope

 FOCUS ON
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The ASH-DOME pictured is 126 (3.8m) Model REB housing
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The public is invited during scheduled open houses.

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 News Notes To get astronomy news as it
breaks, visit skypub.com/newsblog.

SUPERNOVAE I Long-Ago Blasts Littered Earth

it, Breitschwerdt says. The supernova
explosions are like spoons: they stir the
iron-60 into the surrounding medium.
And that has to be calculated in detail to
nd how long it takes to travel to Earth.
The calculations show that two superno-
vae one that occurred 2.3 million years
ago and one that occurred 1.5 million
years ago contributed roughly half of
all the iron-60. The rest comes from the
other supernovae.
A second paper in the same issue of
Nature by Anton Wallner (Australian
National University) reports iron-60 in
crust samples from four dierent loca-
MICHAEL SCHULREICH

tions in the Pacic, Atlantic, and Indian

This simulation shows the mass density distribution of iron-60 associated with the Local Oceans. This evidence is exactly what sci-
Bubble (foreground) and the neighboring Loop I bubble 2.2 million years ago. entists expect to see if supernovae rained
the isotope down across the entire globe.
Although the supernova theory
Radioactive iron and simulations of a heavyweights have already gone super- isnt new, the new papers led a bit of a
nearby stellar association suggest that, nova. Using the surviving relatives of the bandwagon. Leticia Fimiani (Techni-
roughly 2 million years ago, supernovae stars that created the Local Bubble, the cal University of Munich) and her team
showered Earth with debris. team estimated the masses of those pre- announced a week later in Physical Review
Scientists have long suggested that sumed dead and determined when they Letters that iron-60 levels in Apollo lunar
supernovae could explain an isotope of would have exploded. According to those samples match what these supernovae
iron thats embedded in the crust deep calculations, 16 supernovae in this stellar would have deposited.
under the Pacic Ocean. The isotope, family went o like popcorn during the But besides a brilliant ash and some
iron-60, has a half-life of only 2.6 million past 13 million years. debris, the explosions probably had little
years, so the layers must be the result of The team then calculated how much eect on Earth. Supernovae have to be
something that happened more recently. iron-60 would have come from the much closer to do any real damage, says
This isotope is almost exclusively created supernovae and how long the isotope Adrian Melott (University of Kansas).
in supernova explosions. would have taken to reach Earth. Its like What we call the kill zone where you
The other hint is the Local Bubble, a if you put milk in your coee, the milk get a really big mass extinction is like 8
vast peanut-shaped and plasma-lled cav- starts to di use out, and then you take or 10 parsecs [26 to 33 light-years], he says.
ity in which the Sun lives. The death of the spoon and stir it in order to distribute SHANNON HALL
stars in whats now the Scorpius-Centau-
rus association carved out this bubble.
Now Dieter Breitschwerdt (Berlin
Institute of Technology) and colleagues
have put these pieces together to pinpoint
MISSIONS I Hitomi Rescue Called Off
which supernovae did the deed. The The Japanese space agency JAXA ended the mission. The failure is a major
results, published April 7th in Nature, announced on April 28th that it will end blow for X-ray astronomers. An observa-
show that two supernovae, both roughly recovery attempts for its Hitomi X-ray tory-class replacement probably wont hit
300 light-years away, could explain much satellite. A series of problems with the the launch pad until at least 2028, with
of the iron. spacecrafts self-orienting systems led the European Space Agencys Athena,
All stars are born in clusters. A clus- to out-of-control rotation that ung o although smaller missions will launch
ters highest-mass stars die rst. So when several parts of the observatory, including before then. Read the autopsy report at
astronomers spot a cluster made of only the solar panels. Losing the solar panels http://is.gd/hitomidead.
low-mass stars, they assume the missing deprived Hitomi of power and eectively DAVID DICKINSON

10 August 2016 sky & telescope

SOLAR SYSTEM I A Moon for Kuiper Belts Makemake
Of the four dwarf planets now recog- at others. Thats likely if were seeing the years. Far-infrared observations by the
nized in the outer solar system, Pluto, moons orbit nearly edge on and if its not Spitzer and Herschel space observato-
Eris, and Haumea all have at least one too distant from Makemake itself. As the ries showed that Makemakes surface
moon. The fourth, Makemake, seemed to team points out in a write-up posted April wasnt radiating heat in a way thats
be the odd dwarf out. Astronomers used 25th to the preprint arXiv site, the Hubble consistent with one material. Instead,
the Hubble Space Telescope to search for images really dont constrain the orbit well. Parker explained via Twitter, it seemed
companions in 2006 but turned up noth- Uncertainties aside, the moons dis- like most of Makemake was very, very
ing. Now theyve turned up something. covery appears to solve an observational bright, but a small part of it must be dark
Images taken in April 2015 show an puzzle that has nagged astronomers for and warmer. The dark, warm spectral
object traveling together with Makemake, component could come from this moon.
which is currently some 52.4 astronomi- If MK2s surface is very dark just 4%
cal units (7.8 billion kilometers) from the reective then it has a diameter of
Sun. Its 1,300 times fainter than Make- 175km, or 12% Makemakes size.
make itself. And thats about all that Alex Parker says that another round of Hub-
Parker (Southwest Research Institute) ble imagery could be scheduled as early
and his three codiscoverers know about as this summer, but more likely early
this thing, whose ocial designation next spring. Once the team pins down
is S/2015 (136472) 1 but which they MK2s orbit, theyll quickly deduce the

AL .
nicknamed MK2 when announcing its bulk density of Makemake, estimates for

ET
ER
which range from 1.4 g/cm3 (mostly ice)

RK
existence this spring.
PA
EX
L
The problem is that the object shows ES
A
/A to 3.2 g/cm3 (mostly rock), even though
/
A SA
clearly in Hubble images from April 27, N frozen methane dominates its spectrum.
2015, but not in another set recorded just A Hubble Space Telescope image taken April If the four dwarf planets moons were
two days later. Parkers team concludes 27, 2015, reveals a moon (arrowed) around the all created by collisions, their ubiquity
that MK2 is playing hide and seek with distant dwarf planet 136472 Makemake. The suggests that giant collisions are a com-
observers, hiding in the glare of Make- companion, nicknamed MK2, is 0.6 arcsecond mon theme in the Kuiper Belts evolution.
make at some times and popping into view away from Makemake. J. KELLY BEATTY

GALACTIC I Milky Ways New Neighbor fuse, Crater 2 is much fainter than those
companions, 1/100 as luminous as Sagit-
Astronomers have discovered a feeble Now, the list of known dwarfs has tarius and 1/10,000 as bright as the Large
giant: one of the largest dwarf galaxies just added one of its largest members: Magellanic Cloud. The result appears in
ever seen near the Milky Way. Crater 2. Gabriel Torrealba (University of the July 1st Monthly Notices of the Royal
The standard model of cosmology, Cambridge, UK) and others discovered the Astronomical Society.
which suggests that dark energy and dark dwarf galaxy in survey data collected at the The discovery of Crater 2 may help
matter govern the universes evolution, pre- Very Large Telescope in Chile. The team unlock an ongoing puzzle in the Milky
dicts many more small galaxies near the used specialized software to spot over- Ways evolution. Some dwarfs cluster in
Milky Way than what weve observed so far. crowding among stars, searching for dim their orbits, and Crater 2 is no exception:
Dwarfs should be the building blocks of clumps of old, evolved suns that marked the dwarfs orbit lines up with that of the
larger galaxies like our own, so the lack has an ancient stellar population separate from Crater globular cluster, as well as those
puzzled astronomers are they not there, the youthful Milky Way disk. of the Leo IV, Leo V, and Leo II dwarf
or are we just not seeing them? Crater 2 lies 391,000 light-years from galaxies. The similar orbits suggest that
With the advent of large surveys such Earth. That makes it one of the most dis- these objects might be a group that fell
as the Sloan Digital Sky Survey and the tant dwarf galaxies found. And at 6,500 together into our galaxys gravitational
Dark Energy Survey, observers have begun light-years across, it comes in fourth in well. Astronomers have recently found
to identify hard-to-nd dwarf galaxies. size among our galaxys neighbors, after similar groups near the LMC, suggest-
Theyve spotted dozens over the last 15 the Large and Small Magellanic Clouds ing that such group captures might have
years. But theory suggests perhaps even and the torn-apart Sagittarius dwarf helped build our galaxys halo.
hundreds more have yet to be discovered. galaxy. But because its incredibly dif- JOHN BOCHANSKI

Sk yandTelescope.com August 2016 11

 News Notes

GALACTIC I Distant Dwarf Discovered with ALMA SCIENCE & SOCIETY

Waters supercomputer to analyze the $100M for Probes to
ALMA ring, they found a dwarf galaxy
hidden within the depths of the back- Alpha Centauri
Y. HEZAVEH (STANFORD UNIV.) / ALMA (NRAO / ESO /

ground galaxys distorted image. (Its

NAOJ) / NASA / ESA / HUBBLE SPACE TELESCOPE

marked by the white dot near the left The Russian billionaire Yuri Milner,
arc in the image.) The dwarf, a neighbor who last summer committed $100 mil-
of the elliptical, contains the mass of a lion to boost SETI searches to a new level
billion Suns. Although it doesnt emit (S&T: Nov. 2015, p. 10), announced on
observable light itself, the dwarf neverthe- April 12th a second, far more ambitious
less has enough mass to add its own dis- $100 million project. Breakthrough
tortion to the background galaxys image. Starshot will conduct research and devel-
The researchers report in an upcoming opment toward accelerating gram-scale
Astrophysical Journal that they also found interstellar probes to 20% of the speed
This composite, false-color image shows hints of even smaller clumps, presumably of light, using lightsail technology and a
a massive elliptical galaxy called SDP.81 dominated by dark matter as this dwarf 100-gigawatt laser array on Earth.
(center, from Hubble Space Telescope) is, oating in SDP.81s halo. All together, The laser array would boost the
surrounded by the light from a distant the clumps match whats expected from probe out of Earth orbit by aiming at the
background galaxy (red, imaged by simulations modeling the evolution of the probes super-reective lightsail and,
ALMA) thats been gravitationally lensed universe in the presence of dark matter with radiation pressure, accelerating it
by SDP.81. The ring is 3 arcseconds (see page 11). The elliptical and its dwarf to one-fth the speed of light in the two
across. When Yashar Hezaveh (Stanford are roughly 4 billion light-years away. minutes the mini craft is within laser
University) and others employed the Blue MONICA YOUNG range. It will have to do this without
vaporizing the sail or probe. The lasers
would then take a day to recharge their
batteries (from a dedicated power plant),
EXOPLANETS I Nearby Earth-size Planets before sending o the next probe.
The nanoprobes would take only 20
Forty light-years away, a star just consuming observations of the smallest, years to get to Alpha Centauri, if they
one-tenth the size of the Sun holds three faintest stars until the robotic 0.6- survive both the laser blast and the trip.
Earth-size planets in orbit, where none meter TRAPPIST (Transiting Planets and In theory, as each zips through the star
was expected. Although the worlds prob- Planetesimals Small Telescope) began its system, a tiny camera and atmosphere
ably arent habitable, their proximity to work in 2010 at La Silla in Chile. analyzer would grab pictures and data on
Earth makes them excellent targets for In the May 12th issue of Nature, the any planets there. Then it would trans-
attempts to observe any atmosphere they authors report 11 signals of objects pass- mit these data 4.3 light-years back to
might have. ing in front of a star, called TRAPPIST-1. Earth using a compact laser. The total
The star is an M8 red dwarf, contain- Two planets, TRAPPIST-1b and TRAP- mass of each probe, including power
ing only 8% of the Suns mass and emit- PIST-1c, made nine of the 11 transits, supply, camera, sensors, processors, ne-
ting only 5% of its luminosity. Its whats orbiting their star every 1.5 and 2.4 days, navigation thrusters, and that amazing
known as an ultracool dwarf, a class of respectively. The two planets are so close transmitter, is to be just a few grams.
objects with eective temperatures less to the star that theyre probably tidally If you think this sounds impossible,
than half that of the Sun. (Technically, locked with it. youre in good company. But for years
the term also includes brown dwarfs.) The last two transit signals might be now, blue-sky engineering analyses
Some scientists suspected that such from a third planet, 1d. The team couldnt have concluded that while this technol-
small stars might not host planets. pin down its exact orbit. ogy is rather beyond us at present, it
Smaller stars should form with smaller Planets 1b and 1c arent in their stars could come into reach if Moores Law
planet-forming disks around them, and habitable zone. The third planet might continues, if materials science and
ultracool dwarfs might have such small lie in the habitable zone, or beyond it ultra-micro manufacturing develop
disks that they wouldnt be able to form there isnt enough information on its as hoped, and if lasers keep getting
even tiny, rocky planets. According to orbit yet to tell. Regardless, the planets cheaper and more powerful. Milners
Michal Gillon (University of Lige, could be a great chance to study exo-Earth $100 million will go toward investigat-
Belgium), who led the new study, the atmospheres, previously out of reach. ing whether all of this can happen.
controversy was enough to dissuade time- MONICA YOUNG ALAN MACROBERT

12 August 2016 sky & telescope

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 News Notes

IN BRIEF SOLAR SYSTEM I Saturn Moons Could Be Young

BY CAMILLE M. CARLISLE
Planetary scientists suspect that some how they could have interacted, given
Did Fermi Detect LIGOs Merging of Saturns moons may be only 100 mil- their current locations and orbits. The
Black Holes? Scientists with NASAs Fermi lion years old. team found that the moons cant have
Gamma-ray Space Telescope say that the Saturn waltzes through space sur- migrated much from where they rst
observatory detected a weak, 1-second rounded by an entourage of 62 moons. formed. But that doesnt make sense if
burst just 0.4 second after LIGO sensed the Alongside its lone gallant, Titan, orbit theyve been orbiting the planet from
merger of two black holes (S&T: May 2016, an assortment of icy, midsize moons, the solar systems early days: Saturns
p. 10). The ash was so weak that it didnt their diameters ranging from Mimass tides are just too tenacious the moon
trigger the space telescopes onboard alert 400km (250 miles) to Rheas 1,525 km Enceladus and its tidal-triggered geysers
system (partly because the burst went o (948miles). Together, they have a mere conrm that.
underneath the spacecraft) or show up 1/20 as much mass as Titan does. Inter- Instead, the team argues, the mid-
in data from the European Space Agencys spersed are a vast collection of moonlets. size moons can only be about 100 mil-
Integral satellite. Furthermore, astronomers In terms of numbers, Saturns retinue lion years old. The moons formed from
dont expect the black holes to have set o matches that of the king of the planets, a ring of debris, born from the collisions
a light show: any emission would have to Jupiter, whose current satellite tally is of large precursor moons, the team
come from gas, and merging black holes of 67. Yet Jupiter boasts a more glamorous suggests in the April 1st Astrophysical
these masses (a few tens of solar masses) court with its four large Galilean moons, Journal. (The researchers exclude Titan
should have swept up all surrounding mate- and it doesnt have any midsize moons. from the list of phoenix moons.)
rial during their prolonged fatal approach. Yet Planetary scientists have long won- Cuks team oers a test: craters. If
based solely on timing, Valerie Connaughton dered why Jupiter has come out so much the midsize moons are indeed young,
(Universities Space Research Association) the winner when it comes to big moons. they wont have had time to build up
and her colleagues estimate in their paper In 2013, for example, Erik Asphaug a perfectly homogenous peppering of
on the preprint arXiv site that theres only a (Arizona State University) and Andreas pockmarks. Instead, craters on moons
0.2% probability Fermi would have detected a Reufer (then at University of Bern, Swit- within Titans orbit (all the midsize
signal by chance so soon after LIGOs. (That zerland) suggested that Saturn started moons but Iapetus) would concen-
probability doesnt take into account whether with a Galilean system of its own, but trate around those satellites equators,
the signal is real.) The two regions on the sky the moons crashed into and obliterated because the moons would have been
that the signals could have come from do one another. The rubble then coalesced exposed to a lot of debris in the plane
overlap for 200 square degrees, or roughly the
into Titan and the midsize moons. of their birth ring but not nearly as
A new paper explores the collision much from other angles. Many of the
area of Cassiopeias W. Read more at http://
idea further. Matija Cuk (SETI Institute) moons are heavily scarred, so itll take
is.gd/fermiligo16.
and his colleagues turned back time dedicated work to tease out whether the
by simulating the icy moons orbital moons have these crater girdles.
Big Bird Neutrino Came from Blazar? evolution and guring out when and CAMILLE M. CARLISLE
One of the most energetic neutrinos detected
by the IceCube Neutrino Observatory (S&T:
Jan. 2014, p. 18) might stress might
have come from a blazar. The neutrino,
MISSIONS I Russian Space Observatory Launches
dubbed Big Bird, had 2 petaelectron volts Russias Mikhailo Lomonosov astro- simultaneously in both optical and
of energy, roughly a hundred times more physics observatory took to the skies gamma-ray wavelengths in a manner
than protons zipping around CERNs Large on April 28th. Named after the Rus- similar to NASAs Swift satellite. The
Hadron Collider. One possible source for sian 18th-century writer and scientist spacecraft will also monitor for poten-
energetic cosmic neutrinos is blazars, but a (also known for his observations of the tially hazardous asteroids.
previous attempt to pair two other IceCube 1761 transit of Venus; S&T: June 2012, The satellite follows a Sun-syn-
blips with blazar ares was inconclusive. p.32), the Lomonosov has a three-year chronous polar orbit. This is a highly
Matthias Kadler (Wrzburg University, mission. The primary target is the inclined, retrograde orbit that precesses
Germany) and colleagues tried again and high-energy regime, including gamma- 1 per day, enabling the spacecraft to
found that the blazar PKS B1424-418 had an ray bursts (GRBs), cosmic rays, and the view Earth at the same local time on
outburst around the same time as Big Bird source of elusive atmospheric ashes successive passes.
arrived in IceCube. But blazars are notorious known as transient luminous events Lomonosov Moscow State University
ickerers, and with a 5% chance of coinci- on the nighttime side of Earth, often will operate the satellite with agencies in
dence, the result is only a hint. The report referred to as upward lightning. In six other countries, including the U.S.
appeared online April 18th in Nature Physics. addition, the satellite will observe GRBs DAVID DICKINSON

14 August 2016 sky & telescope

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 Computational Astrophysics

A Million
STARS

16 August 2016 sky & telescope

 Crashing code, unasked-for black holes,
and months of work lost to mistakes
astrophysicists battled
many foes in their
quest to create the
Holy Grail of star
cluster simulations.
Benjamin Skuse

Long Wang describes his work as code development and data analy-
sis. It sounds unremarkable. But the 27-year-old PhD student, based
at Peking University in Beijing, China, is much more than a program-
mer and number cruncher. Wang has solved a problem in astrophysical
simulations thought so dicult that in 2010 distinguished Professor
Emeritus Douglas Heggie (University of Edinburgh, UK) oered a bottle
of ne whisky to the rst person to solve it. Five years later in December
2015, Heggie happily handed over the prize to Wang.
Wangs achievement? As main code developer on the international
Dragon Simulation Project, he conducted the rst-ever million-body
simulation of a globular cluster: he built a code that describes every
single stars movement and evolution during the clusters entire
12-billion-year history.

Globular Clusters
Globular clusters (GCs) are big balls of old stars. On average they con-
tain well over a hundred thousand stars, densely packed together and
bound by their mutual gravity into a roughly spherical shape. In our
galaxy and others like it, many GCs were born at the galactic beginning,
forming in the growing primordial gas cloud as it attened into a spiral
disk. They are thought to orbit all massive galaxies.
Among the most ancient structures to have formed in galaxies like
our own, GCs have no young stars today. Star formation ceased bil-
lions of years ago, and all of the largest stars exhausted their hydrogen
reserves in the distant past, leaving only stars with masses comparable
to that of the Sun or less.
Despite their age, GCs are hotbeds of activity, with their stars perform-
ing a type of interminable chaotic dance that has enticed great minds
including Laplace, Lagrange, and Poincar. They may even hold the key
to understanding how galaxies form. In distant galaxies, due to the
T
EC
OJ
PR
N
IO
AT

STELLAR COUNTERFEIT The product of thousands of hours of supercomputer

UL
M
SI

time, this simulated globular cluster closely mimics what astronomers nd in real
ON
AG

clusters. Overlaid are snippets of code from the Dragon Simulation.

DR

Sk yandTelescope.com August 2016 17

 Computational Astrophysics

LONG WANG
CODE DEVELOPER Long Wang
and his team wrote and ran the
GLOBULARS GALORE The Andromeda Galaxy has about 500 globular clusters, some of Dragon Simulation that success-
ROBERT GENDLER

which are marked here by yellow dots. Astronomers have found 154 around the Milky Way fully followed four globular clusters
thus far. Clusters are identied based on Paul Hodges 1981 Atlas of the Andromeda Galaxy. through 12 billion years of evolution
(at least, the computer equivalent).

replicating the lives of star clusters through ever more

realistic mathematical models. Unfortunately, in this
respect GC dynamics is neither sh nor fowl: the equa-
tions are too complex to be solved by cunning algebraic
manipulation, yet not complex enough to eectively
apply approximations like those designed to imitate the
dance of atomic particles in uids or gases.
Instead, the equations underpinning the interactions
among the stars of a GC are best solved by a computer
LONG WANG

code called an N-body simulation. An N-body simulation

is a computer program that follows the behavior of a
NO MAN IS AN ISLAND The Dragon team has nine mem- large number of particles (N) over time. Each particle
bers, including Wang; shown here are Mirek Giersz (left), Rainer represents a unit of something whether a protoplanet,
Spurzem (middle), and Sverre Aarseth (right). a star, or even a galaxy. In the case of GC simulations,
each body is a star.
observation limit, GCs might be the only bright tracers As in all astronomical systems involving more than
of star-formation history and dynamics, Wang explains. two bodies, the dynamics inside these clusters is chaotic,
Careful measurements of GCs therefore provide tantaliz- meaning to understand how the system evolves requires
ing insights into galactic and cosmological evolution. numerical analysis, a type of mathematics that uses
But to fully understand these ancient clusters, algorithms to approximate answers to complex problems.
astronomers need to know how they change over time. The code cuts each stars motion into tiny manage-
Thats not something easily done with observations. So able slices of time. In one time slice, the forces exerted on
researchers mimic on computers how stars interact with each star by all the other stars are calculated, and the star
one another and behave at grand scales, then they com- takes a small step forward. But by the time it has moved
pare those results to clusters in the real world. the forces have changed, so they are calculated again and
the next step is taken. And so forth. The smaller the time
A Backwater of Astrophysics slices taken, the more accurate the simulation.
When I was a young post-doc somebody said to me: Unfortunately, for a 10-billion-plus-year GC simula-
Globular clusters thats a backwater of astrophys- tion, each individual star requires many millions of time
ics, who wants to study those? recalls Heggie. But it steps, meaning the more stars in your cluster, the longer
turns out that the subject really did come to life within a it takes to calculate the clusters evolution. The compu-
couple of years of him saying that . . . and its never gone tational eort is proportional to the cube of the number
o the horizon since then. of particles being modeled. Thus, in order to double the
Fueling this interest has been the challenge of number of stars that you can include in your simulation,

18 August 2016 sky & telescope

you need a computer that is eight times as fast (at least), in the number of bodies that could be simulated: from
explains Heggie. Even though computers have been 10,000 in 1996 to 100,000 in 2003, 200,000 in 2012, and,
getting faster for decades processor performance has most recently, 485,000 in 2014 by Heggie.
grown about 50% per year since the mid-1980s, until a
slowdown in the 2000s to about 20% per year this Bugs in the System
cubic relationship has meant the size of simulations has Heggies 485,000-body simulation was run on the kind
grown much more slowly. of PC that you would put under your oce desk, though
Before parallel computing and advanced acceleration on the big side and took around 2 years to complete.
hardware, scientists would be doing well if they could With so much time invested in one simulation, it was
model the evolution of more than a handful of stars. important that there were no bugs. However, after just
What you could do on a desktop PC at that time was one year he noticed something was wrong. The simula-
maybe 100 particles if you were lucky, recalls Simon tion had one unfortunate feature: there was a line in the
Portegies Zwart (Leiden University, The Netherlands). code which meant that black holes would have a much
And even supercomputers of the time could only handle larger diameter than they should have, he recalls. This,
about 1,000 stars. Yet that wasnt good enough: astrono- in turn, meant that they collided and coalesced much
mers needed million-body (and more) simulations, for more often than they should.
two main reasons. First, the majority of GCs start their This type of problem is common to GC simulations.
lives with at least this number of stars. Second, the If you get a result [you dont expect] there are two things
results of smaller simulations cannot be scaled up to you can do: you can distrust the answer, but then you have
model larger clusters the scaling inevitably leads to to reevaluate the code you have been writing; or you have
unphysical behavior. Just as trying to smooth out wallpa- to take it seriously and publish it, oers Portegies Zwart.
per bubbles with your hand leads to more pesky bubbles And thats a bit scary sometimes because there are bugs
appearing elsewhere, xing one problem when scaling in every code the question is, how serious are they?
up smaller simulations always leads to another. By its nature, designing astrophysical models (of
But the computers just werent up to the simulating stars, clusters, or whole galaxies) involves extreme sim-
task. Indeed, at the start of the 1990s, solving the GC plications and assumptions of very intricate processes.
million-body problem was regarded as a pipe dream. As Corinne Charbonnel (University of Geneva, Switzer-
But then came GRAPE (Gravity Pipe) a computer land) elucidates, this can add another level of uncertainty
specically designed to simulate the evolution of a GC and frustration to the mix. Sometimes we need months
and a quantum leap in computing, being the rst in the of computations before we can validate or disclaim each
world to perform a trillion operations in a single second. assumption, and sometimes one single new observation
With GRAPE 4, we could go up to 10,000 particles, invalidates most of the previous work.
Portegies Zwart explains. This jump was absolutely The longest of the four initial simulations Wang has
amazing. GRAPE drove an almost exponential increase done so far took about a year to complete, and so the

A MILLION STARS THROUGH TIME The Dragon team ran four cluster simulations
and created mock observations of their models so that they could compare the simulated
clusters with observed ones. Shown here is the end result of one simulation (left). The
simulation began with 1,050,000 stars and followed their evolution over 12 billion years.
Step by step, the simulation calculated each stars gravitational eect on the others,
even as it tracked the stars aging and deaths. Above, the series of six snapshots show
dierent populations of objects within the cluster after 12 billion years: from left, AGB
stars, white dwarfs, binary stars, black holes, red giants, and main-sequence stars (those
fusing hydrogen in their cores, as the Sun does). Over time, these populations appeared
and grew. The black holes notably settled to the center as the cluster aged. How concen-
trated the cluster became depended primarily on how top-heavy the initial stellar popula-
tion was in terms of mass. Watch two clusters evolve at http://is.gd/dragonsims.
DRAGON SIMULATION PROJECT

Sk yandTelescope.com August 2016 19

 Computational Astrophysics

EDER IVAN
LOOKS LIKE THE REAL THING The Dragon clusters reproduce the properties of the real-world globular cluster NGC 4372, which
lies deep in the Southern Hemisphere. The cluster (left center) appears here with the Dark Doodad.

Dragon team is equally wary of bugs. I am nervous at term presence can dramatically change the evolution of
the start of simulations if something goes wrong, GCs. For example, the team noticed that some binaries
its a disaster! Wang says. I have suered this kind of formed from these black holes will eventually merge and
problem before, once having to restart the simulations emit gravitational radiation very similar to that recently
several times in one project, costing me half a year. detected for the rst time by the Laser Interferometer
Gravitational-Wave Observatory (LIGO) team.
It Works! Most important, though, is that the Dragon team has
Despite these setbacks, the Dragon team last year suc- shown that the code works. I think its an important
ceeded in simulating a million-star GC, causing ripples
of excitement throughout the community. A million-
body direct simulation was something completely crazy The AMUSE Project
till they achieved it, comments Michela Mapelli (Astro-
nomical Observatory of Padova, Italy). Many teams are writing codes to tackle dierent aspects
Published in the May 11th Monthly Notices of the of stars lives, and Simon Portegies Zwart has created an
Royal Astronomical Society, the teams rst results show open-source metacode called the Astrophysical Multi-
that their four simulated GCs, followed over 12 billion purpose Software Environment (AMUSE) to bring them
years, match up so well with both theoretical models and together. AMUSE is a software framework in which exist-
observational data that they can reproduce the properties ing codes modeling stellar dynamics, stellar evolution,
of real-world cluster NGC 4372. hydrodynamics, and radiative transfer can be used simul-
While there is some ne-tuning still to be done, the taneously. Like a structure made of LEGO bricks, a simula-
simulations already conrm that a bunch of stellar-mass tion within AMUSE is made up of individual codes (the
black holes should huddle in clusters cores, persist- bricks), and each code can be added or taken away accord-
ing for billions of years. Before, these black holes were ing to requirements in order to create a new simulation.
expected to slingshot each other out of the GC, due This plug-and-play capability makes AMUSE a very powerful
to close gravitational encounters between them. The framework for astrophysical star cluster simulation.
Dragon simulation shows that the black holes long-

20 August 2016 sky & telescope

step in our ability to simulate globular clusters and star in Wangs code or one of its successors. And it is this
clusters in general, Portegies Zwart remarks. I would constant cross-pollination of new ideas and techniques
have loved to have done this calculation, in all honesty, through collaboration, open-source code projects, and
but I am very happy for him that he did it. Its fantastic. healthy competition that is allowing the small but
Hes not overegging the accomplishment: million-body highly industrious star cluster community to make rapid
clusters have only been modeled approximately up to progress in simulating and understanding these fasci-
now, so the Dragon teams ability to realistically simulate nating and venerable components of the universe.
them on a star-by-star basis represents a completely new Wang and the Dragon teams achievement will
phase in GC science. only accelerate this progress, not only opening up new
scientic realms to explore but also opening the minds
Multiple Populations: of star cluster scientists to just what might be possible
The Next Challenge if they dream big. What I would like to do in the future
With the gravitational million-body problem solved, you is simulate the entire Milky Way, including all the stars
would be forgiven for thinking that GCs will soon return and planets there may be a trillion planets in the
to being a backwater of astrophysics. The truth is quite galaxy, Portegies Zwart envisions. It sounds completely
the opposite. Numerous crucial questions remain. For ridiculous, but if you had said that you can do a million-
instance, Wang and the Dragon team have yet to nd body simulation of a globular cluster 10 years ago it
a way to include stars of dierent ages in their simula- would have sounded ridiculous, too.
tions. Astronomers only discovered near the turn of the If someone does solve the trillion-body problem, one
21st century that stars in GCs can have dierent ages wonders what Heggie might oer as a prize to celebrate
and initial chemical compositions. Before then, scientists the achievement. Perhaps a barrel of whisky?
thought all stars in a GC were created at about the same
time in protogalaxy halos. But more precise observations Benjamin Skuse is a science communicator and writer based
have exposed multiple generations of stars in GCs. As the in Bristol, UK. He has a PhD in mathematics from the Uni-
assumption that all stars formed at the same time under- versity of Edinburgh, where he also had the privilege of enjoy-
pins most theoretical models of these clusters, multiple ing undergraduate astronomy lectures from Douglas Heggie.
generations present a serious challenge.
Two groups in Europe one led by Mapelli and
Mario Spera in the Formation and Dynamics of Stars
(ForDyS) team, and the other by Charbonnel and an
International Space Science Institute team want to
shine a light on this problem, aiming to resolve why
observations suggest not all GC stars were formed over
10 billion years ago. We need to understand if the
mechanisms that lead to the formation of multiple stellar
populations in massive star clusters are universal, both in
time and space, in order to uncover the link between the
two types of clusters, young and old, explains Charbon-
COURTESY LONG WANG
nel. This is crucial to probe the formation of galaxies
and their evolution over cosmic times.
Charbonnel is working on this problem by devising
new models of all types of stars in GCs, incorporating a
number of complex internal processes that should help
WHISKY PRIZE Douglas Heggie (right) presents Long
illuminate how they came to be. Meanwhile, ForDyS Wang with a bottle of single-malt Scotch whisky at a stellar
focuses on star birth near supermassive black holes and science conference in December 2015.
why stars prefer to form close to other stars in clusters.
We are sure that there is a tiny but very important l F U R THE R R E AD IN G
rouge which connects all star clusters in the universe, Long Wang et al. The DRAGON simulations: globular
argue Mapelli and Spera. We are searching for this cluster evolution with a million stars. Monthly Notices of
guiding thread! the Royal Astronomical Society. (May 11, 2016: 1450-65)

The Galactic Trillion-body Problem? Douglas Heggie and Piet Hut. The Gravitational Million-
With so much eort being made to understand the ori- Body Problem: A Multidisciplinary Approach to Star Cluster
gin and evolution of multiple stellar populations, there Dynamics. Cambridge: Cambridge University Press, 2003.
is little doubt that soon these too will be incorporated

Sk yandTelescope.com August 2016 21

 Planetary Nebulae

Meet the
Minkowskis
TED FORTE
The Minkowski catalog of planetary nebulae
will keep you at the eyepiece for years to come.

GERMAN-AMERICAN ASTRONOMER Rudolph Minkowski Minkowskis work more than doubled the number of
ed Hitlers Germany to join the sta of the Mount Wil- planetary nebulae known at the time. In three papers
son Observatory in 1935. His interests were many, and published in the Publications of the Astronomical Society
hes well known for his spectroscopic studies of superno- of the Pacic entitled New Emission Nebulae in 1946,
vae. Less familiar are his studies of gaseous nebulae. In 1947, and 1948, he gave us a catalog of nearly 200 real or
his early years at Mount Wilson, he conducted a survey suspected PNe, as well as a number of other nebulae,
to nd new planetary nebulae (PNe) using an objective some of which are proto-planetary nebulae (PPN). The
prism mounted on the 10-inch Cooke wide-angle cam- PPN are a short-duration phase of stellar evolution that
era. He later obtained slit spectroscopy of the suspected precedes the planetary nebula phase. They typically
planetaries with the 60-inch and 100-inch telescopes. exhibit morphological shapes similar to PNe but have
central stars that arent yet hot enough to ionize their
Find the data table for the Minkowski planetary circumstellar material and produce the characteristic
nebulae discussed here at http://is.gd/MinkPNe. emission of true planetaries.
While Minkowski didnt number the objects in the
32 original lists, the PNe listed in those three papers are
20h 30m 20h 00m 19h 30m 19h 00m 18h 30m
31 now universally recognized by the designators M 1-NN,
M 2-NN, and M 3-NN. Later, Perek and Kohoutek added
M 4-17 additional objects from Minkowskis observations that
then became known as the M 4-NN list. Collectively, all
of these objects can be described as just Minkowski
Planetaries, with the acronyms Min and Mink fre-
+40
quently used in the literature.
CYGNUS
M29 Vega
2 Blink the Mink
M 1-64
Most of the objects in the Minkowski catalog escaped
LYRA detection by generations of visual observers, so its no
wonder theyre considered to be challenging targets and
require some special techniques to detect. Emission in
M57 specic wavelengths distinguishes these objects from
6765 +30 ordinary stars in the eyepiece, so a nebular lter is often
M 1-92
M56 a necessity. Experienced observers of PNe typically own
1
Albireo
Star magnitudes

a variety of lters and regularly employ more than one

2
on any given object.
3
4
PNe normally exhibit strong emission from doubly
5 ionized oxygen (O III) at 500.7nm and 495.9nm, so lters
VULPECULA that pass these wavelengths are the most eective. UHC
6
M27 (ultra-high contrast) lters pass O III as well as a variety
of other wavelengths, making them very eective for

22 August 2016 sky & telescope

BRIGHT BINARY Bipolar planetary nebulae like
Minkowskis Buttery form when an old low-to-
intermediate-mass binary star system ejects its outer
layers. The central star system lights up the shell as
stellar wind spreads gas in opposite directions.

SPACE ART BY CASEY REED

Sk yandTelescope.com August 2016 23
 Planetary Nebulae

most planetary nebulae. The truly narrow bandwidth

19h 00m 18h 30m 18h 00m
lters, like the O III and H-beta, pass a lot less light than
M 4-9 M14
wider band lters, so aperture also comes into play. More
restrictive lters will be of less utility in smaller scopes
M11
since they block so much light as to make detection of
fainter objects more dicult.
M26 Software programs that predict visibility based on
10 contrast thresholds rarely account for the enhancements
M 4-11
SERPENS created by nebular lters. Dont let their predictions of
SCUTUM CAUDA invisibility deter you from attempting detection.
M 1-61 No matter the size of your scope or the passband of
M16
Star magnitudes

2 your lters, the most powerful technique PN hunters

3
4 M17
M18
can employ is blinking. By holding a lter between
5 M 1-22
thumb and forenger and passing it in and out of the
M24
6 light path by sliding it between eye and eyepiece, a PN
M25 M23
20 can be made to blink. The lter dims the entire eld, but
since it preferentially passes the principle wavelengths
2
M21
emitted by the nebula almost undiminished, the PN
M22 M20
stands out from the more dimmed eld stars. It actually
SAGITTARIUS M28
M8 appears to brighten.
The blink eect is usually very subtle, and it takes
M 1-36 good concentration and a lot of practice, but once mas-

M 1-38 tered, youll have a very essential skill at your disposal
that will enable you to pick out a tiny planetary from
among a eld of ordinary stars. The smallest PNe will
benet from the blinking technique; larger disks will
reveal themselves with a lter inserted in the eyepiece. If
your telescope is equipped with a lter wheel or slide bar
that can quickly switch between the ltered and unl-
tered view, it may serve you well, but I nd that even
when I have a lter wheel available, the manual blinking
method is more eective. A range of magnications will
increase the chance of detection.

Getting acquainted
In the August sky, there are more than 90 Minkowski
M1-92 PNe well placed for observing from mid-northern
latitudes, and that number goes up as you move south.
From my location in southern Arizona, 130 are well
above the horizon during August. Most of the PNe
described below can be viewed with an 8-inch scope, but
very few are well enough known to have earned popular
nicknames. There are two notable exceptions, however.
Minkowskis Footprint, M 1-92, is a proto-planetary
nebula in Cygnus. It gets its moniker from a Hubble
Space Telescope image that reveals it as a bipolar nebula
IMAGE: ESA / HUBBLE / NASA / SKETCH: UWE GLAHN

with a very vague resemblance to a footprint. Its quite

COSMIC TRACKS Proto-planetary nebula M 1-92, known
colloquially as Minkowskis Footprint, consists of a white bright, and yet I found it dicult to detect its extended
dwarf surrounded by gas shaped by stellar winds. This shape. Only a slight elongation can be seen in the
composite image combines exposures taken through eyepiece, and since its a reection nebula, lters wont
Hubble-specic lters. The eld of view is only about 36 enhance its visibility. It lies in a fairly crowded star eld
arcseconds across. Sketch above: Viewed at 1465 in a about 20 east of 9 Cygni, adjacent to a 9th-magnitude star.
27-inch reector, M 1-92 shows a distinct two-part struc- Minkowskis Buttery, M 2-9, in Ophiuchus, also
ture with a sharp central star. derives its name from a striking Hubble image that
shows a beautiful bipolar structure that mimics the

24 August 2016 sky & telescope

 M1-68

STEFAN BINNEWIES / JOSEFPPSEL

GHOSTLY GOLDFISH M 1-68, also cataloged as NGC 6765, was discovered by Albert Marth in 1864 with a 48-inch speculum
reector. Under increased aperture and magnication, this planetary resembles a broad-nned carp swimming in a starry pond.

wings of a buttery. Its also known as the Twin Jet Neb- see as a star, but it doesnt reveal its disk without a lter
ula. Without its enticing nicknames, it might get far less and medium to high power. The challenge of detect-
attention, as in smaller apertures its quite challenging. ing objects like M 3-34 is threefold. Concentrated in the
While a 10-inch scope should reveal some elongation, plane of the Milky Way, they often lie in very crowded
it probably takes at least 16 inches of aperture to detect star elds, so the rst hurdle is to locate them precisely.
a bipolar structure. In 30 inches, its quite remarkable, Since its far easier to compare your star eld to your
however. Filters dont seem to enhance the object much map without a lter inserted, this rst step will often
and high power is a must. just pinpoint a likely star with no hint of an extended
Three of the PNe identied by Minkowski were disk. Then conrm its true nature by detecting its emis-
already in the New General Catalogue and two more were sion nebulosity. Successful detection involves the best
listed as IC objects. NGC 6765 (M 1-68) in Lyra and IC combination of lter and magnication through trial
4673 (M 1-36) in Sagittarius, are well placed for observ- and error. Its this added level of diculty that makes
ing this month. NGC 6765 lies a little over 1 west-north- observing PNe so rewarding. Not everyone gets it; PN
west of the globular cluster Messier 56. Its elongated observers are a unique breed, it seems.
north-south and irregular; larger apertures will show Several Minkowski planetaries will be quite easy to
a bipolar structure thats brighter to the north. Apply a see as stars but remain stellar at all powers. Some will
narrowband lter to improve its visibility. I wasnt able to seem to brighten with a lter (we say they respond to
detect the 16th-magnitude central star. a lter) but show no actual disk at any power. Notable
IC 4673, 3 above the spout of Sagittariuss Teapot, examples in the August sky are M 1-61 in Scutum, and
sits in the middle of an arc of four 13th-magnitude stars. M 3-21 and M 1-38 in Sagittarius. All are bright and
It appears as a small disk with a hint of annularity vis- easy and respond to lters, but none can be made to blos-
ible when viewed through a lter. This ring structure som into a disk.
illustrates the importance of applying lters even to the To be honest, only the most dedicated PN observers
objects that are obvious without them the enhance- get satisfaction from observing objects that dier from
ment reveals details that would otherwise be missed. ordinary stars only spectroscopically, so any best of
Minkowski PNe list must contain those objects that
Typical targets exhibit a disk or a ring in backyard telescopes. Fortu-
M 3-34 in Aquila is typical of many of the planetaries nately, there are a number of them in the August sky.
in the Minkowski catalog. Its fairly bright and easy to M 1-64 lies 2 19 north-northwest of the more

Sk yandTelescope.com August 2016 25

 Planetary Nebulae

0h 23h 22h 21h 20h famous Ring Nebula (M57) in Lyra. M 1-64 appears as a
small faint disk in an 8-inch telescope. In larger aper-

tures, a ring structure reveals itself, especially in the
M 2-55 +70 ltered view. Look for the star embedded northeast of
the planetarys center.
Cepheus contains two Minkowski PNe that certainly
belong on the best of list. M 2-51 lies about 54 south-
CEPHEUS east of Zeta () Cephei. Eight inches of aperture show it as

a disk. In my big 30-inch Dob, I see an irregular oval even
without a lter and can hold it with direct vision. Extend
the imaginary line connecting Zeta and Iota () Cephei
M52 another 5.5 northeast to nd M 2-55. Its 1.1 disk can be
+60
seen without a lter but is much enhanced with a UHC
lter. Look for brighter star-like knots in its angular body.

M 4-17 in Cygnus is a small faint disk. Extend a line
M 2-51
through 32 and 31 Cygni, 3 toward the western wing of
the Swan, to nd it. Low power and a lter help reveal
the round nebula, although in my largest scope, its eas-
LACERTA ily seen without a lter.
The Swan holds another ghostly looking disk, M 1-79,
which is found less than 1 northeast of the open cluster
Star magnitudes

2 CYGNUS +50
3 Messier 39. Smaller scopes will easily show a smooth
2
4 disk, especially through a lter. Its surrounded by many
M 1-79 M39
5 faint stars. In larger scopes, a ring structure is apparent
6 as the center darkens to show annularity when a lter is

applied to the view.
Scutum contains the small faint disk of M 4-11 1
THE OTHER RING Below left: The faint star at the north edge south of the globular cluster NGC 6712. At moderate to
of M 1-64 shows in this sketch made at 586 with a 27-inch reec- high power, it can be seen without the benet of a lter,
tor. Right: A 14.5-inch reector reveals M 1-64s ring structure. but its at its best at low power and through an O III lter.

M1-64
IMAGE: MARTIN C. GERMANO / SKETCH: UWE GLAHN

26 August 2016 sky & telescope

M2-55

IMAGE: POSS-II / CALTECH / PALOMAR OBSERVATORY / SKETCH: UWE GLAHN

CEPHEUS SIGHTS Above: M 2-55 appears elliptical or as a elds of the Milky Way. This, of course, is the ultimate
slightly uneven smudge until you pump up the magnication challenge for the observer of Minkowski PNe. For North
and throw on a lter. Look for the star-like knots in its body. American observers, the southern declinations add sig-
nicantly to the diculties, and observers who set a goal
Right: Even without a lter, the view through a 27-inch reector
of observing the entire catalog have their work cut out
at 419 displays M 2-55s annularity and knotty structure.
for them. For dedicated PN fans, however, it can be a real
labor of love and a very rewarding observing project.
Challenge Targets
Some Minkowski planetaries are particularly tough Contributing Editor Ted Forte observes from his home near
objects, where its possible to detect a disk but its Sierra Vista, Arizona.
anything but easy. I oer three challenge objects that,
while easy enough to see as a star, will be devilishly
hard, but not impossible, to detect as a disk. M 1-1 lies M1-1
on the AndromedaPerseus border about 2 north of
51 Andromedae. Its tiny, just 6 in diameter. M 1-22 in
Ophiuchus is only a little larger in listed dimension at
about 9. Its classication implies a ring structure, but
Ive yet to see annularity. M 1-22 is in a busy neighbor-
hood between the globular cluster Messier 9 and the
open cluster Messier 23. M 4-9, 2 41 southwest of Eta
() Serpentis in Serpens Cauda, shows a ghostly disk
even without a lter. These three should present owners
of 8- and 10-inch scopes with a signicant challenge.
Many objects have been known to mimic planetary
nebulae, and, of course, there are some misidentied
objects with Minkowski designations. Ive been fooled
by a few of them. For instance, the eclipsing binary star
POSS-II / CALTECH / PALOMAR OBSERVATORY

V471 Persei has the designation M 1-2, and my logbook

contains the description of a nebulous-looking star that
was easy to see without a lter.
The densest concentration of Minkowski planetaries
is found in Sagittarius. That constellation contains more
than 60 objects from the catalogs, with another 49 in
neighboring Scorpius and Ophiuchus. Nearly all of these
objects are tiny and well hidden among the dense star

Sk yandTelescope.com August 2016 27

 Urban Observing

Visual Filters
for
Deep-Sky Observing
S&T: CRAIG M. UTTER

While not a magic bullet for defeating light pollution,

nebula filters are still a boon for many urban observers.
Those of us interested in observing the universe other class of deep-sky object.
beyond the solar system have a big problem: light pollu- Most nebulae are subtle in the rst
tion. How can we see distant marvels when our skies are place, being barely brighter than
painted pink from countless sodium streetlights? the sky background even when
Our best strategy is to get out from under the light viewed from a dark site. Increase Rod Mollise
dome that covers urban areas and to view instead from a the background skyglows intensity
dark site. How often can we do that, though? We might and theyre just gone. So, are dimmer nebulae out of
get to our clubs observing site once or twice a month, the picture for city and suburban observers? Not at all,
and some of us might make it to a star party at a dark thanks to light-pollution-reduction (LPR) lters.
location only once or twice a year. Most of us want to LPR lters, also known as nebula lters, can make
observe more often than that. the dierence between seeing and not seeing dim
There are tricks to seeing star clusters, and even objects from a suburban backyard. That doesnt mean
galaxies, in the midst of light pollution. Choosing a LPR lters are a replacement for dark skies, though.
large-aperture telescope and an eyepiece that yields They are not. Given the choice between using a lter in
contrast-enhancing, medium-high magnication can my suburban backyard and the view through an un l-
make dimmer objects show themselves to some degree. tered eyepiece out in the country, Ill always take the lat-
But nebulae are another story. These clouds of dust ter. But LPR lters are a help even if they cant perform
and gas are harmed more by light pollution than any magic, and they do have some signicant limitations.

28 August 2016 sky & telescope

 How do LPR Filters Work?
Contrary to what some novices believe, deep-sky lters
dont make objects brighter. Instead they increase
contrast by blocking the bad wavelengths of light pol-
lution. That is, they make the sky background appear
darker in the eyepiece without dimming the target
object. More contrast makes the nebula look better.
The way these lters work is easy to understand. An
LPR lter is a piece of glass coated with multiple layers
of various substances. These coatings have the abil-
ity to block the transmission of certain wavelengths of
light while allowing others to pass. The bandpass of a
lter the range of wavelengths it allows through to
the eyepiece is tailored to the specic purpose of the
lter, and its determined by the exact types and number
of coatings applied to the glass.
LPR lters are typically mounted in cells identical to
those used for photographic lters or the colored lters
used by planetary observers (S&T: July 2016, p. 52). They
screw into the threads machined at the end of the eye-
piece barrel. Almost all modern 1- and 2-inch oculars
feature these standard lter threads.
If you havent picked up on it already, LPR lters

DENNIS DI CICCO
are only good for observing nebulae and then only
emission and planetary nebulae. These lters oer little
advantage for observing star clusters because the light
from streetlights and other light-pollution sources covers TYPICAL TARGET The Veil Nebula, a giant supernova
the same range of wavelengths as that emitted by stars. remnant in Cygnus, is a prized target for many observers. In
LPR lters dim starlight as much as they dim articial modestly light-polluted skies its visibility can be signicantly
skyglow and thus do not improve contrast for these improved by viewing through an O III lter.
objects. For the same reason, LPR lters are also ineec-
tive on reection nebulae, since these objects shine only enhance galaxy viewing to some extent, dimming the
by the reected light of stars. background a little without also dimming the galaxy
Finally, since the light we see from galaxies is mostly much, but Ive never considered any LPR lter very help-
starlight, LPR lters dont improve their visibility either. ful when Im viewing galaxies.
There is, sadly, no such thing as a galaxy lter. Some
observers have commented that a mild LPR lter can Three Types of Filters
One look at the lter section of an astronomy dealers
website or catalog reveals a confusing number of types
and brands. Once you understand a simple fact, though,
itll be easy to make a choice. Filters fall into three
general classes: broadband (so-called mild or deep-sky
lters), narrowband (UHC or ultra-high-contrast), and
line (ultra-narrowband). As for the dierent brands, LPR
lters from most manufacturers are basically similar,
but it can still be true that you get what you pay for,
as more expensive lters are often made with premium
optical glass that can oer better performance than
some inexpensive ones do.
Broadband lters have a wide bandpass; they allow a
broad range of wavelengths to pass through to the eye-
HELPFUL AIDS For observers who must contend with piece. They are the least expensive LPR lters but often
prove the least eective. The sky background with a mild
ROD MOLLISE

some level of articial skyglow, light-pollution-reduction (LPR)

lters can improve the visibility of many emission nebulae. lter can be almost as bright as without it, and therefore
you gain only a little increase in contrast.

Sk yandTelescope.com August 2016 29

 Urban Observing

SKYGLOW DECONSTRUCTED Evolving streetlight

LED technology has changed the nature of light pollution. During
Streetlight
the 1970s the skyglow above Boston was dominated by bright
Boston 2016
emission lines from the then-ubiquitous mercury-vapor street-
Boston 2001 lights. By 2001, however, widespread use of sodium-vapor
lighting added more emission lines to the skyglow, making it
Boston 1979 increasingly dicult for LPR lters to block all the oending
Mercury-vapor wavelengths. Now LED streetlights, with their nearly continu-
Streetlight
ous spectral emission across visual wavelengths, are rapidly
replacing older lights.
Broadband lter
FILTER TYPES The three principal types of LPR lters
Narrowband lter described in this article are distinguished by their transmis-
DENNIS DI CICCO (2)

sion characteristics, which were recorded with a spectrograph

O III lter
for this illustration. Because narrowband and O III (line) lters
Sunlight allow progressively less light to pass through to the eyepiece,
they work best with medium- to large-aperture telescopes.

Narrowband (UHC) lters are the bread and butter light-gathering power of at least a 4-inch telescope.
of deep-sky observers. One of these can dramatically Caveats? Line lters work on most, but not all, plan-
improve the appearance of emission nebulae and will etary nebulae, and they work on some, but not all, emis-
also improve many planetary nebulae. While UHCs sion nebulae. The Orion Nebula, M42, for example, looks
darken the sky background substantially, they are not so worse to me with an O III than without. On the other
strong as to render dim stars in the eld invisible, so they hand, it makes the Veil Nebula, a supernova remnant,
present the most attractive and normal-looking views. look much improved. Unlike UHC lters, O III lters
Line lters have a still narrower bandpass, admitting dim eld stars considerably, sometimes even to the point
only a small slice of wavelengths. The most common of making focusing dicult.
types are O III and hydrogen-beta (H-beta or H) lters. The hydrogen-beta lter is engineered to pass only
I nd the O IIIs by far the most useful line lter, since the blue-green light of this spectral line. If an O III does
they suppress everything except the spectral lines of not work on all nebulae, the H-beta does not work on
doubly ionized oxygen that are a major component of the most. It is often referred to as the Horsehead Nebula
light of planetary nebulae like M57, the Ring Nebula. lter, since its mainly used by observers pursuing that
These lters can do an amazing job on planetary nebulae faint object. The H-beta will also work on a few other
or any other nebula that radiates strongly in O III light. similarly dim objects, like the California Nebula, but its
O III lters are fairly dense and thus work best with the certainly not a general-use lter.
DENNIS DI CICCO (3)

CONTRAST IMPROVEMENT Left: These images of the Crescent Nebula in Cygnus give a rough approximation of how the nebulas appearance
is enhanced when viewed through an O III lter. The back-to-back exposures through clear (left) and O III (right) lters were made when the nebula
was in a part of the sky moderately brightened by light pollution from Boston. Right: In a low-power eld of view, many small planetary nebulae are
dicult to distinguish from stars. But they can often be identied by rapidly moving an LPR lter, especially a narrowband or O III lter, in and out
between your eye and eyepiece, causing the stars to icker while the planetary remains relatively constant.

30 August 2016 sky & telescope

 PRIZED NEBULA As described in the text, the Horsehead

CHUCK MANGES
Nebula in Orion is one of the few emission objects best seen
with a hydrogen-beta line lter.

Which Filter To Buy First? eective on all objects, but theyve been a big help for
A UHC-type narrowband is without question the best backyard deep-sky observers over the three decades since
rst LPR lter. It works on more objects than an O III they became popular.
lter, and many more than a broadband lter. A UHC Unfortunately, their eectiveness will likely be
might not be optimum for some planetary nebulae, but compromised in the future. Cities, mostly just the larger
almost all will be improved by it. ones at this time, are beginning to convert from high-
After you have a UHC, the next most useful lter for and low-pressure sodium streetlights to LED lighting.
your kit is the O III. It wont help with as many objects as Unfortunately, LEDs are broad-spectrum emitters com-
the UHC, but those that it does enhance are sometimes pared to sodium lights; their wide range of wavelengths
spectacularly improved. The Veil and Helix nebulae, for is not as easy to lter out.
example, look far better with an O III than with a UHC. Some of the light from these new streetlights falls in
From there? You might not need any more lters. the bandpass of a UHC lter but not the most intense
Round out your collection with an H-beta if you want portion of their emission. The same is true for O III
to be fully equipped, but if youre like me you will use it lters. Their bandpass falls within the spectrum of
only rarely. an LED but not in the highest intensity part. In other
How much are your choices going to cost? LPR lters words, both lters can still be eective but not as
are not cheap. They are specialized low-production eective as they are with sodium-vapor lights. Also, we
items, and they are complicated to manufacture. Expect probably have some breathing room, since replacing
to pay around $100 for 1-inch UHC or line lters, and sodium lights with LEDs is expensive and will take time
about twice that much for 2-inch versions. to implement.
You wouldnt think thered be much to using LPR It will happen eventually, however; that seems inevi-
lters. Screw one into your eyepiece, and away you go. table. So we amateur astronomers need to continue our
Actually theres a secret to using them eectively and crusade to reduce light pollution, led by the Astronomi-
if you dont know it, you will be disappointed by their cal League and the International Dark-Sky Association
performance. (darksky.org), by encouraging the use of sensible light
If a lter is to do its best, you must not allow ambient xtures and, especially, limiting the number of lights to
light to enter the eyepiece from the eye end. When stray no more than those really needed.
light enters the eyepiece and that will happen unless Even without the threat of LED lighting, LPR lters
your eye is tightly jammed up against the eye lens the are hardly a panacea. They are not 100% eective at dark-
ocular will be ooded with ambient light and you will ening the sky background, and they only work on a rela-
see less with the lter than without. tively small percentage of objects. However, they have
There is a simple x, however: use a rubber eyecup allowed me to view many deep-sky marvels that would
on the eyepiece. If the ocular doesnt have one, you can otherwise have been invisible from my backyard, and
buy cups that t over almost any eyepiece. Or cup your theyve enriched my experience of amateur astronomy
hands around the eyepiece when youre viewing to shield immeasurably. In other words, they are worth every
it from ambient light. Best of all, especially under brutal penny and then some.
light pollution, is to cover your head and eyepiece with a
dark cloth. Veteran observer and telescope guru Rod Mollise writes
LPR lters can be highly eective. Theyre not a frequently on astronomical topics in this magazine and at
complete cure for light pollution because they are not uncle-rods.blogspot.com.

Sk yandTelescope.com August 2016 31

 Measuring Bent Starlight

A DO-IT-YOURSELF

Relativity Test
Using o-the-shelf equipment during going to be a very challenging experiment!
The most recent attempt to do this, organized by the
next years total solar eclipse, you can University of Texas in 1973, required moving 6 tons of
prove that Einstein really was right. equipment to Africa and leaving the telescope assembled
but untouched for 6 months in a guarded shed. The
researchers used a 200-mm-aperture refractor with a
DONALD BRUNS 2.1-meter focal length, and they recorded images during
the eclipse on 12-inch glass plates. Despite their heroic
In the long and colorful history of scientic expeditions eorts, the result still had an uncertainty of 11%.
to view total solar eclipses, two are particular standouts. With todays technology, a capable amateur should
On July 29, 1878, a small group of visitors that included be able to get a far better result with much less eort. In
Henry Draper and Thomas Edison watched totality from order to measure a tiny deection of as little as 0.02 arc-
near Rawlins, Wyoming (see page 36). They were look- second, excellent stellar images are needed and thats
ing for Vulcan, the hidden, close-in planet thought to entirely possible today. CCD cameras have replaced glass
inuence the orbit of Mercury. The second, on May 29, plates, image-processing software has supplanted scan-
1919, involved Sir Arthur Eddingtons measurement of ning microdensitometers, and satellite-based star cata-
the deection of starlight and a triumphant conrma- logs have eliminated the need to measure star positions
tion of Einsteins general theory of relativity. six months before or after the eclipse. All that is left to
Next year, 139 years after Draper and Edison ventured do is careful planning and attention to detail.
West, I will be in Wyoming to repeat the 1919 experi-
ment that made Einstein famous. Im going to measure Equipment and Experiment Design
the Suns deection of starlight too, and to succeed Ill By analyzing all of this projects requirements and com-
need to determine star positions accurate to a small frac- paring them with a wide variety of amateur telescopes
tion of an arcsecond, during only 140 seconds of totality, and cameras, I selected an optimum combination of
with no second chance if something goes wrong. Its optics and detector. Your picks might be slightly dier-
ent, but heres a recap of my rationale.
Stars For the telescope, I chose the highly portable Tele
apparent position Vue-NP101is. This apochromatic refractors 101-mm
Newtons angle = 0.85 arcsecond aperture can capture 10th-magnitude stars with 1-second
Einsteins angle = 1.7 arcseconds
Stars exposures, and its diraction limit is only 1.3 arcseconds
S&T: LEAH TISCIONE; SOURCE: DONALD BRUNS

true at a red-light wavelength of 630 nm much smaller

position
than the 2-arcsecond daytime seeing I expect to
encounter. The objectives 540-mm focal length provides
a 2 eld of view with a medium-format camera.
Earth Since Ill need to pinpoint the centers of star images
Sun to within 0.02 pixel, those stars falling near the edges
and corners of each frame must be as sharp as the ones
in the center. The NP101is has a at, color-free image
BENDING LIGHT The apparent position of a star seen near plane, perfect for creating these very accurate star
the solar limb is deected a very small amount by the Suns images, and I can adjust the focuser so that the camera
gravity. Einsteins general theory of relativity correctly predicts remains perfectly square to the optical axis. Finally, the
the observed deection angle. (Not shown to scale.) rugged, lockable focuser allows me to slew to multiple

32 August 2016 sky & telescope

STARS AND SPECTACLE A feathery corona, created by carefully calibrating and combining 55 images, surrounds
the Moons silhouette during the total solar eclipse of August 1, 2008. This composite also reveals more than 450

DONALD BRUNS
stars, including the Beehive Cluster (upper right of the Sun). Right: The authors relativity test kit consists of a Tele
Vue-NP101is refractor, FLI Microline 8051 CCD camera, and Software Bisque MyT Paramount and eld tripod.
2008 MILOSLAV DRUCKMLLER, PETER ANIOL, & VOJTECH RUIN

sky locations with minimum risk of camera movement, would make determining the stars exact centers very
essential for good calibration. dicult. A monochrome camera like the 8051 provides
Next came the choice of imager. My pick was the the spatial resolution I need.
8-megapixel monochrome Microline 8051 CCD from Since the eclipse is far from home, Ill also need a
Finger Lakes Instrumentation, a camera that Ive used tracking mount on a portable tripod. For the NP101is
on previous astrometric projects. Its pixels are only 5.5 refractor, my Software Bisque MyT Paramount on its
microns wide, a perfect match for the focal length of eld tripod is perfect. I can either do a good polar align-
the NP101is, yielding 2.1 arcseconds per pixel. I opted ment the night before or use a handheld GPS to orient
against using a larger-format camera, as that would have the mount to within about 1 of Polaris and the celestial
required more time to digitize each image. Besides, any pole on eclipse day (especially if I change sites to avoid
stars recorded far from the Sun will have a very small cloudy weather). The Paramount features permanent
deection and wouldnt help much in the nal analysis. periodic-error correction, or PEC, and the resulting
By contrast, the 8051s fast 12-megapixel-per-second tracking error is less than 1 arcsecond just what I
digitizing rate will be critical during my brief time in need for perfectly round star images.
totality. Moreover, its interline CCD sensor requires no
mechanical shutter; this avoids vibrations and ensures Capturing the Stars
that every star is exposed simultaneously. I didnt want An important pre-eclipse planning task is to determine
a color sensor, whose dierent lters on adjacent pixels how dim a star I can record near the Sun during totality

Sk yandTelescope.com August 2016 33

 Measuring Bent Starlight

1.10 down to 0.02 arcsecond? An astrometric rule of thumb

Light-deection coecient (1+ )/2 is that the achievable accuracy for a given star equals its
image radius divided by its signal-to-noise ratio (SNR).
1.05 If I only measure stars with SNRs of at least 14, then at

S&T: LEAH TISCIONE; SOURCE: C. M. WILL

worst Ill get positions accurate to 1.3/14 = 0.1 arcsecond;
Hipparcos adding the eects of atmospheric turbulence might
1.00
increase this error to 0.2 arcsecond.
Wyoming
2017 However, thats for only one image. Averaging
0.95 multiple measurements reduces the error by the square
root of the number of images. So, for 25 images, the
positional errors would drop by a factor of ve, yield-
1920 1960 1970 1980 1990 2000 2010 ing 0.04 arcsecond for the worst errors. Brighter stars,
Year of experiment with higher SNRs, yield better accuracy, so I expect the
average error to just reach my 0.02 arcsecond goal if
PAST EXPERIMENTS Astronomers have attempted to mea- everything goes right!
sure the deection of star positions during only a few eclipses To make the deection calculations, I need to know
over the past century, while Hipparcos made a very precise the image scale to within a few parts per million. Since
determination from space. The vertical scale is normalized to the telescopes focal length changes with temperature
the deection of star positions predicted by Einstein. and air pressure, this means Ill have to calibrate the
image scale obtained during totality. So Ill devote some
therell be no time for trial-and-error! After searching of those precious seconds to record two reference star
hundreds of websites, I found only one eclipse chaser elds on opposite sides of the Sun (as shown in the
whod used a calibrated, monochrome astronomical cam- sky chart below).
era. In March 2006, Christian Viladrich of France took Immediately after totality starts, Ill shoot the rst
an SBIG STL-11000 camera to Egypt to record the inner one, about 8 west of the Sun, for 30 seconds. There,
corona. His exposures were only 5 milliseconds long, far from the bright corona, the gravitational deection
so I stretched his image brightness by 200 to simulate should only be 0.06 arcsecond. Next Ill spend 60 sec-
a 1-second exposure. Then I estimated the background onds recording the eld surrounding the solar corona.
brightness levels near the Sun to calculate which stars Finally, Ill slew the telescope one more time to record
would be easily visible. The result? More than 60 stars the reference eld on the Suns east side for the last 30
brighter than magnitude 12 should be in the eld of seconds of totality. With these references, the deection
view; with a limiting magnitude of 10, I hope to get good images should be perfectly calibrated.
astrometric measurements from 8 of them.
Assuming moderately poor seeing, I expect my star TARGET FIELDS The author intends to record three star elds
images to average close to 2.8 arcseconds (1.3 pixels) during the 2 minutes of totality provided by August 2017s
across. So how am I going to measure their positions solar eclipse. Stars are shown to magnitude 10.5.

50 d 8
+16 10h 30m 10h 00m 9h 30m

33
42
26 /
11
52 46
+14 s 7
37
Reference eld Reference eld
Eclipse eld 23
34
i
+12
LEO 21 18
Regulus 19 j 2
53 3
Star magnitudes

4
+10 31 5
k
l 45 6 6
7
49 44 t
8
3 9
+8
S&T: LEAH TISCIONE; SOURCE: DONALD BRUNS

34 August 2016 sky & telescope

Modern Star Positions
All previous deection experiments required imaging YO U C AN D O IT T O O!
the same star eld six months before or after the eclipse Visit http://is.gd/DIY_Relativity_Test for a more detailed
in order to determine the star positions to sub-arcsecond explanation of the authors plans. If anyone wants to
accuracy and the telescope and camera had to be left duplicate or help on this project, contact him directly at
untouched for the duration to minimize mechanical dbruns@stellarproducts.com.
errors. In the 1990s, the Hipparcos satellite generated a
very good astrometric reference catalog, obviating the
need for a year-long quiescence. However, those mea-
sured positions are 25 years old, and their uncertainties
are now typically 0.1 arcsecond. The U.S. Naval Observa-
torys newer UCAC4 catalog is better (S&T: Dec. 2012,
p. 16), but its 0.05-arcsecond errors still fall short for this
experiments needs.
By this September, however, the situation should
improve dramatically! Thats when the European Space
Agency plans to release the rst star catalog compiled by
its Gaia satellite. Launched in 2013, Gaia is measuring
a billion stars with an accuracy of 0.000024 arcsecond

CHRISTIAN VILADRICH
(S&T: Apr. 2014, p. 10). While the spacecraft needs more
time to measure parallax or proper motion, this rst
catalog will oer exquisitely accurate positions just in
time for the 2017 eclipse.
But Ill be down on the ground, not in space, and
SIMULATED STARS Using a calibrated monochrome eclipse
atmospheric refraction will shift the apparent positions image from 2006, the author simulated the stars he expects to
of stars. I can calculate those osets, and to get the most record near the Sun with a 1-second-long exposure during next
precise results Ill need to monitor the local air tem- years eclipse. Stars near the corners should have a gravitational
perature to within 2F and the atmospheric pressure to deection of 0.4 arcsecond, while the closest one at lower right
within 3 millibars. should be deected by 0.7 arcsecond.
Then theres the issue of lens distortion, which
all refractors have to some degree. Fortunately, I can this dry run, though the results should show a gravita-
compensate for this by taking images near the zenith at tional deection of zero (since the Sun isnt nearby). This
night and comparing the resulting star positions with will prove the technique and give me condence in the
the Gaia catalog. This should yield corrections reliably real eclipse experiment four months later.
good down to 0.01 arcsecond and to a negligible level Ill set up my experiment in Wyoming, based on its
if I average lots of stars. high altitude and cloud-free forecast (S&T: Jan. 2016, p.
Once I have all the images, Ill run them through 22). Even so, Ill follow the day-before weather forecasts
multiple astrometric programs (such as Pinpoint, Astro- closely and move the experiment if needed. Ill also be
metrica, and Prism) to determine the star locations in automating the pointing and exposure sequences so
pixel coordinates and to identify the individual stars. that, after I press Start, I can enjoy the spectacle!
I hope the outputs from these programs will agree to This challenging experiment repeats the measure-
the 0.01-arcsecond level, but I might have to experiment ments that made Einstein famous. Careful planning and
with their various user-adjustable parameters. Then Ill dependable equipment should help avoid disappoint-
remove the eects of optical distortion and atmospheric ment. In many ways, this is a much simpler experiment
refraction before comparing the corrected star locations than any previous ground-based attempt and the
with the Gaia star catalog. results should be far better. And if things dont go as
planned? Well, theres always the next U.S. opportunity
Ready, Set, Go! to see totality: Texas in 2024!
This eclipse wont aord the chance for any do-overs, but I
can run a test well before the eclipse date to verify various A retired optical physicist, Don Bruns enjoys reading about
sources of positional error. The sky during totality is about exceptional historical experiments and this is his rst
as bright as when the Sun lies 6 below the horizon. And attempt at reproducing one. He received valuable help from
it turns out that my three planned star elds are roughly George Kaplan and John Bangert of the USNO, as well
at the same elevation during evenings in late March and as Al Nagler of Tele Vue, Greg Terrance of FLI, Christian
early April. Ill test my planned exposure sequence during Viladrich of France, and Suresh Rajgopal.

Sk yandTelescope.com August 2016 35

 Go West, Astronomers!

The Great American Eclipse

of the 19th Century
In the summer of 1878, astronomers and tourists were
newly ready to swarm into the Wild West.
William Sheehan
The total eclipse of the Sun thats coming on August 21, and adventure; his books helped to paint the image of the
2017, is already being called the Great American Eclipse. West as it took shape in the American mind. He arrived
Its path of totality will sweep across the continent from at Westport, Missouri, says historian Bernard de Voto, on
Oregon to South Carolina, while all of North, Central, and the very edge of the frontier . . . that saw all the energies
upper South America will experience a partial eclipse. of Manifest Destiny at last in vigorous motion energies
Millions will gaze in wonder at perhaps the most stunning which, before the year was out, would capture Oregon
predictable celestial phenomenon, while taking in some of and California and the Mexican Southwest and make the
the most majestic scenery of the continent: the best clear- nal destruction of the Plains Indians inevitable. Those
sky odds are for the West. energies pushed westward the Oregon Trail, the Bozeman
The 19th century also boasted a Great American Eclipse Trail, and the Bridger Trail, the latter providing an alter-
on July 29, 1878. Not only was it the last total eclipse nate route to the Montana gold elds skirting the region
visible over much of the North American continent in controlled by the Sioux, Cheyenne, and Arapaho. Then fol-
the 19th century, it was the rst to be widely observed by lowed the transcontinental railroad, which, said poet Walt
astronomers in the western United States. And it came at Whitman, joined distances like magic.
an opportune moment both in astronomy and in the his- By 1878 numerous towns and settlements, in various
tory of the American West. stages of incipient civilization, dotted the territory from
There was no question that it would be a spectacle. which to view the eclipse. For the rst time the region
The maximum duration of totality was 3 minutes 11 including the grandeurs of Yellowstone (recently painted
seconds. The Moons shadow, some 116 miles wide, rst in epic canvases by Albert Bierstadt and Thomas Moran,
touched land in northeastern Asia, then crossed to Alaska, and designated in 1872 as the worlds rst National Park)
Canada near the Pacic coast, and southeast across the stood wide open to astronomers.
vast western United States and its territories. Darkness
ROCKY MOUNTAIN SPECTACLE The solar eclipse of July 29,
swept over Yellowstone and the Wind River Range, down
1878, was sketched by St. George Stanley at Snake River Pass, Col-
through Medicine Bow and into Colorado, crossing Longs
orado. The scene was now one of surprising beauty, he wrote,
Peak, then Boulder, Denver, Colorado Springs, and Okla- for Pikes Peak, far away to the south, still remained in sunlight,
homa Indian Country before entering the Gulf of Mexico looming in rosy outline, while the horizon that a moment before
between Galveston and New Orleans. was ochre, now glowed with red, gold, pink, and lilac. The
Just 30 years before, the Boston aristocrat Francis corona gleamed. . . with a pale nebulous light, and the heavens
Parkman, Jr., had set out westward in search of Indians above acquired a shade of blue that mortal can not describe.

36 August 2016 sky & telescope

 HARPERS WEEKLY

Sk yandTelescope.com August 2016 37

 Go West, Astronomers!

CARBON COUNTY MUSEUM, RAWLINS, WY

EDISON & FRIENDS Thomas Edison (second from right) made the trip to Rawlins, Wyoming, with one of his lesser-known inventions:
a tasimeter, with which he hoped to measure infrared radiation from the solar corona and nd its contribution to the Suns heat. Others
here include (in order to the left of Edison) the partys leader, astronomer Henry Draper of New York; Mrs. Draper; Mrs. Watson; and James
Craig Watson, whose observations of possible intra-Mercurial planets was the most controversial report from the eclipse.

And they were eager to go. Both American and Euro- Superintendent of the Nautical Almanac Oce, pro-
pean (mostly English) astronomers relished the prospect posed to go to Creston itself. So did William Harkness
of mixing scientic endeavor with adventure and sightsee- and A. N. Skinner of the U.S. Naval Observatory, Alvan
ing. Thanks to an $8,000 appropriation from Congress, Graham Clark of the famed family of instrument-mak-
the U.S. Naval Observatory determined to establish no ers, and the French astronomer-artist Leopold Trouvelot.
less than eight observing stations between Montana Ter- On his arrival, Harkness described nding a little bit
ritory and Texas. Edward Singleton Holden, then at the of a hamlet, situated almost on the backbone of the
U.S. Naval Observatory, hoped to set up the northernmost continent, being only 2 miles east of the divide which
outpost at Virginia City, where gold had been discovered separates the watershed of the Atlantic from that of the
in 1863. He invited C. H. F. Peters of New Yorks Hamil- Pacic. The country in the vicinity is at and uninterest-
ton College Observatory to come along. The latter politely ing. . . [though] the horizon is bounded by the distant
declined. You go to Montana, he wrote, adding, Take peaks of the Rocky Mountains. . . . The place contains
care of not being scalped by the Indians! only two small cottages, and its population consists
The concern was real enough. The year before, the of seven white adults, three children, and six Chinese
U.S. Army had fought the Nez Perce in that general laborers who keep the track in order.
region, while only two years earlier the Sioux and allied This kind of rude accommodation was typical of what
tribes led by Crazy Horse and Sitting Bull had anni- the astronomers would nd. But though their shelter
hilated Custer and elements of the U.S. 7th Cavalry and grub might be spartan, the huge skies of Wyoming
at Little Big Horn. To the south, conict was brewing and Colorado were breathtaking, while the clear moun-
with the Utes of northern Colorado. In the end, Holden tain air was so limpid that the satellites of Jupiter were
decided that discretion was the better part of valor and claimed to be easily visible with the naked eye.
set up farther south, on the at roof of the Teller Hotel at Pioneering astrophysicist Dr. Henry Draper and his
Central City, Colorado. wife, the New York City heiress Anna Palmer Draper,
The northernmost eclipse station now became lonely headed to Rawlins, Wyoming, another railroad town,
Creston, Wyoming Territory, on the Union Pacic boasting a population of 800 and a good hotel. They trav-
railroad. The rail line fortuitously followed the narrow eled with Thomas Alva Edison of Menlo Park, New Jer-
eclipse path in the south-central part of the Territory and sey, who at 31 was already celebrated for his invention of
oered several choices for observers. Simon Newcomb, the phonograph. He brought along one of his inventions:

38 August 2016 sky & telescope

a pocket-sized device he called a tasimeter to measure
infrared radiation, by which he hoped to determine the

PORTAL TO TEXAS HISTORY, UNIV. OF TEXAS LIBRARIES

heat output of the solar corona while the body of the Sun
hid behind the Moon.
To Rawlins also went University of Michigan astrono-
mer James Craig Watson and his wife Annette. Watson,
renowned for his many asteroid discoveries, was in the
hunt for the elusive (in fact nonexistent) planet Vulcan.
A total eclipse would provide an excellent chance to
discover this small planet supposedly circling close to
the Sun. Astronomers worldwide had been trying to nd
it, after the French astronomer Urbain J. J. Le Verrier
NEAR THE ECLIPSE TRACKS END At the S. W. Lomax
predicted its existence from a tiny unexplained increment
farm near Fort Worth, Texas, astronomers stand by their tele-
(some 43 arcseconds per century) in the rate of precession scopes awaiting the eclipse and a possible glimpse of Vulcan.
of Mercurys perihelion. Mistaken sightings had seemed
to conrm the new planet. Only in 1915 was Mercurys
drift revealed to be not a perturbation by an unseen
planet, but a result of gravitys behavior under Einsteins
general theory of relativity (S&T: Dec. 2015, p. 18).
Other prominent astronomers ooding to the eclipse
path were Allegheny Observatory director and solar
astronomer Samuel Pierpont Langley, who climbed the
14,000-foot Pikes Peak to obtain the best possible views
of the corona. Princeton solar astronomer Charles Young
and visiting English barrister and amateur astronomer
Arthur C. Ranyard went to Cherry Creek, near Denver.
The U.S. Naval Observatorys George W. Hill and New
York amateur Lewis Swift set up in Denver itself. So did
Nantucket astronomer Maria Mitchell and ve of her
NANTUCKET MARIA MITCHELL
female students. Asaph Hall, renowned for his discov- ASSN. / THE TROUVELOT
ASTRONOMICAL DRAWINGS
ery of the two satellites of Mars a year earlier, went to La
Junta in southeastern Colorado. David Peck Todd headed
for Dallas, Texas, among the southernmost sites. Many
members of the public, newspaper reporters, and amateur
astronomers came as well. A few were serious observers.
Most, like today, were tourists or accidental onlookers.
On the day of the eclipse, the skies over most locations
were wonderfully clear. The various observational pro-
grams unfolded as planned, though with mixed results.
At Rawlins, Henry Draper succeeded in photograph-
ing the spectrum of the corona. Poor Mrs. Draper was
assigned to a subservient role for the men; she was nom-
inated timekeeper, and dutifully counted the seconds of
totality from inside a tent, blind to the spectacle, lest the
sight of it unnerve her and cause her to lose count!
At Rawlins strong westerly winds were nearly con-
tinuous, leading Watson to move his instruments to an
isolated Union Pacic rail stop at Separation, about mid-
way between Rawlins and Creston. He was joined there
SOUVENIRS Middle: Faring better than Mrs. Henry Draper, who
by another late arrival, Simon Newcomb. Sheltering
was consigned to a tent in Rawlins, Wyoming, the famed Nantucket
their equipment in the lee of a semicircular sand dune, astronomer Maria Mitchell and ve of her female students awaited
they prepared to wait out the partial phases of the eclipse the eclipse at Denver. Below: This magnicent if not entirely
in eager anticipation of the scant minutes of totality, accurate chromolithograph of the eclipse was made by the French
when they would scour the solar vicinity for Vulcan. artist-astronomer Etienne Leopold Trouvelot, recording his impres-
During the excitement of the eclipse, Watson spotted sions from Creston, Wyoming.

Sk yandTelescope.com August 2016 39

 Go West, Astronomers!

Vancouver

NORTH

18
78
DA KOTA
Seattle Spokane Great Falls

JU
Pullman MON TA NA Bismark

LY
WA SH I NGT ON Butte
Bu
M I N N E SO T

29
Billings
Portland
and 2 0 17 AU G
U S T 21 SOUTH
DA KOTA
W YOM I NG
Eugene Bend Rapid City
Idaho
Boise Falls Jackson
OR E G ON I D A H O Pocatello
Casper IOWA
Twin Falls N E BR A SK A

Fort Collins
N E VA DA Salt Lake

S&T: GREGG DINDERMAN

City Denver
Reno C OL OR A D O
U TA H Aspen
Colorado K A NSA S
San Francisco Springs

HISTORY REPEATS During the August 2017 solar eclipse, scene was now one of surprising beauty, for Pikes Peak,
the path of totality will cross that of the 1878 eclipse for parts of far away to the south, still remained in sunlight, looming
Wyoming and southeastern Idaho, including Jackson and por- in rosy outline, while the horizon that a moment before
tions of the Shoshone National Forest. was ochre, now glowed with red, gold, pink, and lilac.
Stars and planets came out, while the corona gleamed. . .
two unidentied stars, whose positions he marked on with a pale nebulous light, and the heavens above acquired
the makeshift paper setting circles with which he had a shade of blue that mortal can not describe. After totality
equipped his telescope. He maintained and would ended, the great peaks that had been darkened began to
continue to maintain until the end of his life that they reappear from the gloom, and looked like ghosts. The
were intra-Mercurial planets. Most astronomers would only disappointment was that Vulcan. . . managed to hide
later accept the verdict of C. H. F. Peters, who argued himself from our scrutiny. Harpers Weekly worked from
that Watson had merely misidentied two eld stars. Stanleys sketch to publish an engraving of this scene that
Langley obtained lovely views, and made detailed lled its front page. It was much reprinted in astronomy
sketches, of the coronal streamers from the top of Pikes books for decades after.
Peak. Lewis Swift reported two suspicious objects which These were accounts of the city slickers from back East.
at rst were thought to conrm Watsons vulcans. Only Fewer reports exist about the way the Native Americans
later did they prove not to agree in position, and eventu- perceived the event. Mabel Loomis Todd, in her Total
ally they too were widely discredited. Todd, also on the Eclipses of the Sun (1894), recounts that a resident of Fort
lookout for Vulcan, was frustrated by haze. Sill, Oklahoma Indian Territory, claimed the Indians were
Meanwhile, ordinary observers submitted their badly frightened; some threw themselves upon their
reports such as St. George Stanley, a correspondent knees, others ung themselves at on the ground, faces
for Harpers Weekly, who with a party of ladies and down, others cried and yelled in terror. One old man,
gentlemen, set up near Georgetown, Colorado, at the more resourceful, stepped from the door of his lodge with
Argentine or Snake River Pass upon the Sierra Madre, pistol in hand, carefully directed his aim, and red at the
elevation 13,156 feet. This point of observation was cho- blotted luminary. It was unanimously voted, she says,
sen for. . . its altitude, and the extended view obtained that the timely discharge of that pistol was the only thing
from its summit, embracing a wonderful panorama of that drove away the shadow and saved them from the pub-
the great ranges of the Saguache, Escalente, and San- lic inconvenience that would have certainly resulted from
gre de Christo west and south, the continuous line of the entire extinction of the Sun.
the Sierra Madre north and northwesterly, and a broad So passed the Great American Eclipse of July 1878.
sweep of stretching plains to the east.
From this vantage point, Stanley and his associates Contributing editor William Sheehan, co-author of Celes-
watched the shadow of the Moon approach from the north- tial Shadows, divides his time between psychiatry and
west, covering in succession Longs Peak and the Mount astronomy in Flagsta, Arizona. He will observe the next
of the Holy Cross. Suddenly they too were enveloped. The Great American Eclipse from near Jackson Hole, Wyoming.

40 August 2016 sky & telescope

 OBSERVING
August 2016

In This Section
42 Sky at a Glance 48 Celestial Calendar
48 Perseids to Get a Jupiter Boost?
42 Northern Hemisphere Sky Chart 50 Resolve a Stars Disk Naked-Eye!
43 Binocular Highlight: Lasso the Lizard 51 A Blue-Sky Aldebaran
Occultation on August 25th
44 Planetary Almanac
52 Exploring the Moon: Twin Basins with a Twist
45 Northern Hemispheres Sky:
Summertide Sailing 54 Deep-Sky Wonders: Scutums Gems

46 Sun, Moon & Planets: Additional Observing Article

Augusts Double Convergences 22 Meet the Minkowskis
Rimae Archimedes and Palus Putredinis stretch southeast of Archimedes Crater (left) to the Montes Apenninus (lower right).
PHOTOGRAPH: CHAD QUANDT

SkyandTelescope.com August 2016 41

 OBSERVING
Sky at a Glance Using the Map orth

Go out within an hour of a time

AUGUST 2016 listed to the right. Turn the map
3 DUSK: Use binoculars to pick up Jupiter low in around so the yellow label for the
the west about 20 minutes after sunset. Look 16 direction youre facing is at the PE
_
bottom. Thats the horizon. Above RS
to its lower right for Mercury and another 8 lower it are the constellations in front
EU

3h
S
right of Mercury for Venus. of you. The center of the map is OPARD
CAMEL
Fa a ALIS
overhead. Ignore the parts of c
4 DUSK: The thin crescent Moon pairs with Mercury the map above horizons in
about 15 below and right of Jupiters gleam after

g
youre not facing.

a
sunset; use binoculars to tease them out. Edge 9

E
EXACT FOR LATITUDE C
Do lust
lower and farther right to nd Venus. 40 NORTH. ub er CA
le
SS
5 DUSK: Vivid Jupiter shines less than 2 above the IO

waxing crescent Moon. IA

PE b

`
7 DUSK: The Moon hangs between Spica and dim- a

mer Gamma () Virginis in the west-southwest. _

AN
Polaris
` a

M3
DAWN: On this or the next few mornings watch

D
11

RO
M
the east-southeast horizon about 20 minutes
52
CE

M
before sunrise for the heliacal rising (rst visibility) PH

ED
EU `
of Sirius as it emerges from the Suns glare.

A
b S

_
LATE NIGHT TO DAWN: The Perseid meteor

LAC
1112

shower peaks on the morning of August 12th. + _

ER
Great Square
Viewing should be best in the early morning

of Pegasus

TA
hours; see page 48.

M39

Deneb _
23, 24 EVENING: Mars forms a vertical line about

f
6 long with Antares below and Saturn above,
0
PISCES

+
h

Northern
61
about halfway up the southwestern sky.

PEGASUS
Facing East

Cross
C Y G N U S M27 S A G

b
a

R
MORNING TO AFTERNOON: The Moon occults

Vega
25
_

M29

Aldebaran mid-morning or early afternoon for

b
d
much of the United States and Central America;

_ LYRA
r

a
see page 51.
c

Albireo

`
VU

M57
`
LPE
M15
27 DUSK: Venus and Jupiter appear extremely close

CU

a
together very low in the west; see page 46.

LA
DEL
e

IT
EQU

PHI

TA
Planet Visibility SHOWN FOR LATITUDE 40 NORTH AT MID-MONTH Alt c
_

air

NUS
ULE

a
AQ

SUNSET MIDNIGHT SUNRISE

US

` _
AQ
U

Mercury W Visible through August 14

M2

UI
AR

d e
LA
Venus W 70
IU

SE
R
M (CA PEN
S

Mars S SW Au oon UD
g1 A
7 M11
_ S C
Jupiter W b U T
U M M16
` Moon
Saturn S SW
C
M

Aug 14
A

M17
30

M25
Moon Phases
R

E C
IC

L I + M
2
O

New August 2 4:44 p.m. EDT First Qtr August 10 2:21 p.m. EDT P T
I C
R
N

M22
U

Full August 18 5:26 p.m. EDT Last Qtr August 24 11:41 p.m. EDT m
o
S
Fa

S UN MON TUE WED THU FR I S AT

c

c S A G IT T
g 21h
in

1 2 3 4 5 6 SE A R IU S

Galaxy
7 8 9 10 11 12 13
Double star CORO
N
Variable star AUSTR A 40$
14 15 16 17 18 19 20 ALIS
Open cluster
Diuse nebula 1
21 22 23 24 25 26 27
Globular cluster
Planetary nebula
28 29 30 31 28 29 30 Facing
 Mathew Wedel
Facing
When Binocular Highlight
Late June 1 a.m.*
6

LYN
X
Early July
Late July
Midnight*
11 p.m.*
Lasso the Lizard
+60$ I am a connoisseur of a particular class of open
Early August 10 p.m.*
clusters: those set in star elds so rich that the

9h
f
g
Late August Nightfall clusters seem to merge into the Milky Way. A
k W *Daylight-saving time. favorite of mine in this genre is NGC 7243 in the
N
e g constellation Lacerta, the Lizard.

in
R
The cluster is a fairly easy catch about 1.5

c
O

Fa
INEO west of 4 Lacertae. Its elongated from east to
h M L
west and at 10 looks like a narrow, westward-
+
+80$ M82 pointing arrowhead. At 15 a dense swarm of

`
M81 R
JO unresolved stars gives the eastern half of NGC
A SA
_
M R
U ` 7243 a nebulous glow, whereas the brighter
h
s stars in the western portion look more like a
MINOR
a i
classic open cluster. To my eyes it appears as a
URSA g r e j miniature version of M8, the Lagoon Nebula in
pp
Di ig b Sagittarius, only with the nebula and cluster
B
+80$
`
r
portions reversed from east to west.
lco
The clusters neighborhood also makes for

O
Dipper
a
_ Thuban & A zar
NE ICI

c i

LE
`

Little M
compelling viewing. NGC 7243 sits in a rich
S
C A T

band of stars that trends from northeast to

N
A
VE

c
southwest, with the clusters arrowhead shape
51

_
M

f d
d
+60$ cutting across the band almost at right angles.
`

e
S
TES

Although this stream of distant suns is richest

NICE

i
j DRACO
h
A

12 in the clusters immediate neighborhood like

COM
`

BERE
M3
BO

`
foothills building to a mountain peak it can
a
`

Facing West
be traced out for almost 10. And its book-
2
M9

BOREALIS +

ended by two additional open clusters, NGC

_
3

CORONA
d

Zenith
M1

7209 on the southwest end and NGC 7296 at

d
_

the northeast. If we imagine Beta () Lacertae

/

ES
c

as the head of the constellations stick-gure,

s

Arcturu

b
UL

GO

the swath of stars between NGC 7209 and NGC

T S

a
b

)
RC

U N

7296 forms a leash running to the lizards neck.

`

VIR

Grab your binos and go for a walk!

A P E
HE

+20$
P

g n
( CE R
S `

Au oo
7
M
_

_
O R
5
M

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Spica

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0$
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M12 b
M10
S S `
HU on r vi ew
) I UC A
Mo g 10 ula
PH R oc
O c
I Ba Au _ `
in

L
5 b

d
M23 ` 7296
i _ 7243
21 20$ Saturn b
M20  M39
_ m Ma/rs m
M8 M19
Anta
res M4 LACERTA
SW

o CYGNUS
S 15h
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g

R P n
S M6 M62
S C
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M7 S Fa
PU
LU
h
p 1
+
d
0
c 1 k
e
18h 2
3 Star
4 magnitudes
g South
Sk yandTelescope.com August 2016 43
OBSERVING
Planetary Almanac
Mercury Sun and Planets, August 2016
August Right Ascension Declination Elongation Magnitude Diameter Illumination Distance

Sun 1 8h 45.5m +18 01 26.8 31 31 1.015

Aug 1 11 21 31
31 10h 37.9m +8 39 26.8 31 41 1.009
Venus
Mercury 1 10h 15.6m +11 27 23 Ev 0.2 5.9 72% 1.130

11 11h 04.2m +4 59 27 Ev +0.1 6.8 59% 0.992

21 11h 37.6m 0 28 27 Ev +0.4 7.9 44% 0.847

1 16 31 31 11h 49.2m 3 18 21 Ev +1.1 9.5 24% 0.710

Mars Venus 1 9h 47.5m +14 54 15 Ev 3.8 10.1 96% 1.648

11 10h 34.6m +10 32 18 Ev 3.8 10.3 95% 1.614

21 11h 20.3m +5 43 21 Ev 3.8 10.6 94% 1.575

31 12h 05.0m +0 38 23 Ev 3.8 10.9 92% 1.533

1 16 31
Mars 1 15h 44.9m 22 46 110 Ev 0.8 13.0 87% 0.722
Jupiter
16 16h 11.8m 24 00 102 Ev 0.5 11.6 86% 0.804

31 16h 45.4m 25 05 95 Ev 0.3 10.5 85% 0.889

Jupiter 1 11h 31.8m +4 17 43 Ev 1.7 32.1 100% 6.146

31 11h 53.6m +1 54 20 Ev 1.7 30.9 100% 6.387

Saturn 1 16h 33.1m 20 16 121 Ev +0.3 17.5 100% 9.479

16
31 16h 33.6m 20 23 92 Ev +0.5 16.7 100% 9.952

Saturn Uranus 16 1h 30.4m +8 47 119 Mo +5.8 3.6 100% 19.441

Neptune 16 22h 50.7m 8 18 162 Mo +7.8 2.4 100% 28.988

Pluto 16 19h 04.9m 21 18 142 Ev +14.2 0.1 100% 32.355

16 The table above gives each objects right ascension and declination (equinox 2000.0) at 0 h Universal Time on selected
dates, and its elongation from the Sun in the morning (Mo) or evening (Ev) sky. Next are the visual magnitude and
Uranus equatorial diameter. (Saturns ring extent is 2.27 times its equatorial diameter.) Last are the percentage of a planets disk
illuminated by the Sun and the distance from Earth in astronomical units. (Based on the mean EarthSun distance, 1 a.u.
Neptune is 149,597,871 kilometers, or 92,955,807 international miles.) For other dates, see SkyandTelescope.com/almanac.
Planet disks at left have south up, to match the view in many telescopes. Blue ticks indicate the pole currently tilted
Pluto 10"
toward Earth.

+40 8h 6h 4h 2h 0h 22h 20 h 18h 16h 14 h 12h 10 h

GEMINI RIGHT ASCENSION Vega
Castor
+30
BOTES
Pollux CYGNUS +30
Pleiades ARIES
+20 PEGASUS HERCULES Arcturus +20
LEO
28 25 PISCES
TA U R U S Uranus AQ UI LA Venus
VIRGO +10
Betelgeuse OPHIUCHUS
Jupiter
Procyon 22 AQ UARI US
0
ORION E Q U AT O R Mercury 0
LIBRA 7
10 Rigel 10
Sirius Neptune Aug 17 18 10
DECLINATION

CETUS 13 CORVUS
ERIDANUS Pluto Saturn
20 20
CANIS ECLI
CAPRI CO RN US PTIC Mars
MAJOR
30 Fomalhaut H Y D R A 30
SCORPIUS
LOCAL TIME OF TRANSIT SAGITTARIUS
40 10 am 8 am 6 am 4 am 2 am Midnight 10 pm 8 pm 6 pm 4 pm 2 pm 40

The Sun and planets are positioned for mid-August; the colored arrows show the motion of each during the month. The Moon is plotted for evening dates in the Americas when its waxing (right
side illuminated) or full, and for morning dates when its waning (left side). Local time of transit tells when (in Local Mean Time) objects cross the meridian that is, when they appear due
south and at their highest at mid-month. Transits occur an hour later on the 1st, and an hour earlier at months end.

44 August 2016 sky & telescope

OBSERVING
Fred Schaaf welcomes your
Northern Hemispheres Sky comments at fschaaf@aol.com. Fred Schaaf

Summertide Sailing
Search for treasure as you navigate the Milky Way river.

And now the sun had set, and all the colours of the world
and heaven had held a festival with him, and slipped one The Great Rift
IC 4756
by one away before the imminent approach of night . . . the

reies in the deeps of the forest were going up and down, and
NGC 6633
the great stars came gleaming out to look on the face of Yann.
Ser
. . . And so Yann bore us magnicently onwards, for he
was elate with molten snow that the Poltiades had brought
him from the Hills of Hap, and the Marn and Migris were
swollen full with oods; and he bore us in his might past Oph
Kyph and Pir, and we saw the lights of Goolunza. Lord
Dunsany, Idle Days on the Yann, 1912

Last month in this column, we began a long voyage

DAVE YOUNG / CC BY 2.0

south from Cygnus on the Heavenly River, the Milky Sgr
Way. We can continue it in a luxuriously idle cruise, as
if we were on a fantasy river like the Yann, described in
a story written by one-time chess and pistol-shooting
champion of Ireland, Edward John Moreton Drax Plun-
kett Lord Dunsany. large naked-eye clusters one of them huge just 3
Milky Way of the Rift and the two channels. apart. The larger of the two, 52-wide IC 4756, rests 4.5
Beginning in Cygnus, the vast tongue of dark interstellar west-northwest of the beautiful low-power double star
dust clouds called the Great Rift splits the bright Milky Theta () Serpentis (Alya), the most northerly star in the
Way lengthwise into two bright channels. line of Serpens Cauda (the Serpents Tail, which projects
One sight of interest that shines right in the Great Rift perfectly into the Great Rift). The smaller cluster, some
or rather in its foreground is the Coathanger. A low- 3 northwest of IC 4756, is NGC 6633. Though smaller
magnication telescopic view shows that this tiny aster- than its neighbor, its still quite big (27 wide) and bright,
ism (not a true cluster, though it is often called Brocchis shining at magnitude 4.2 though like IC 4756, its
Cluster) looks astonishingly like a coathanger made of rather loosely structured. Use very low magnication on
stars. The Coathanger lies near Sagitta, the Arrow, about both when you turn your scope or binoculars on them.
one-third of the way along the line from Altair to Vega We credit astronomy writer and editor Terence Dick-
in the small constellation Vulpecula, the Fox. Can you inson with coining the name the S-O Double Cluster
detect it with your unaided eye? In dark skies you should (Serpens-Ophiuchus Double Cluster) for this cluster pair
at least see it as a 1, 3.6-magnitude patch or blip of (IC 4756 is in Serpens, NGC 6633 just over the border in
brightness against the Rifts dark background. The main Ophiuchus). The S-O Double Cluster is profoundly dif-
pattern of Sagitta small though much bigger than the ferent than the famed Double Cluster in Perseus but
Coathanger lies in the glow bordering the Rift. intriguing nonetheless, especially for naked-eye sailors
What shines in or in front of the dimmer channel of of the Milky Way.
Milky Way, the one that peters out in northern Ophiu- Yann or Anduin? The poet W. B. Yeats is said to have
chus? The intriguing area of Beta () Ophiuchi (Celbal- admired Dunsanys Idle Days on the Yann. But which
rai) and the big naked-eye cluster IC 4665; the V-shaped fantasy river is the Milky Way most like? Maybe the great
Taurus Poniatovii asterism (a defunct constellation); and north-south river of J. R. R. Tolkiens Middle-earth, the
Barnards Star. Anduin. But Ill make that comparison next month,
But I like to point out the pair of lesser-known yet fas- when we nish our Milky Way trip with the richness of
cinating objects just upstream from this area. Theyre Scutum, southern Serpens, Sagittarius, and Scorpius.

Sk yandTelescope.com August 2016 45

OBSERVING
Sun, Moon & Planets

Augusts Double Convergences

Observe a series of planetary get-togethers this month.

Welcome to a short but wonderful burst Regulus) very low in the west at dusk, Unfortunately for viewers at mid-
of planetary conjunctions. Some occur well also see Mars make a weeks-long northern latitudes, Mercury doesnt
very low in evening twilight including march in the south, moving from the appear any higher in the next few weeks,
an ultra-close meeting of planets Venus head of Scorpius to pass right between even as it reaches greatest elongation on
and Jupiter. But in addition to the group- Saturn and the Scorpions heart, Mars- August 16th. Venus, passing little more
ings of Venus, Jupiter, and Mercury (and colored Antares. than 1 from Regulus on August 4th and
5th (use optical aid to view the pairing),
DUSK edges just a bit higher as the weeks pass.
Denebola Dusk, Aug 45 On August 1st, Jupiter, Mercury, Jupiter, however, moves noticeably lower
20 minutes after sunset
Regulus, and Venus in that order, in twilight each week, on its way to a
from upper left to lower right form grouping of Venus, Mercury, and Jupiter
Jupiter a line nearly 27 long in the west after later in the month.
sunset. But look early in twilight and The spectacle of three planets passing
Moon bring binoculars, because Venus is only each other in the second half of the month
Aug 5 about 4 high even just 20 minutes after will present an observing challenge for
the Sun goes down, as seen from lati- viewers at mid-northern latitudes.
Mercury
Moon tude 40 north. Magnitude 0.1 Mercury On August 19th Mercury, at a maxi-
Venus
Aug 4 gleams about 8 upper left of magnitude mum altitude of 6 and dimmed to
Regulus 3.9 Venus, which sets a bit more than magnitude +0.3, shines its closest to
45 minutes after the Sun. Mercury sets Jupiter, which is about 4 above it. Venus
approximately 15 minutes later, and Jupi- is 8 right of Mercury, closer to the Sun.
Looking West ter follows in another 45 minutes. On August 28th Mercury, seriously faded
to magnitude +0.8, comes its closest to
Venus, hovering about 5 below and left
Dusk, Aug 1113 Dusk, Aug 23 of the brighter planet.
1 hour after sunset 30 minutes after sunset
Moon
But the best conjunction for mid-
Moon
Moon
Aug 12 Aug 11 northern viewers occurs on August 27th,
Aug 13 when Venus and Jupiter draw as close as
Saturn 0.1, depending on your viewing location.
Saturn
From southern South America you can
Mars Mars see this meeting in a dark sky, where the
Antares Antares planets lights will blend together when
viewed with the naked eye. Use binocu-
SCORPIUS lars to pick up the duo as the Sun sets
(but do not look at the Sun!). Telescopes
Cats SCORPIUS will show the disks of the two planets
Eyes
together even in a fairly high-magni-
cation eld of view. Jupiters dim disk
measures about 31 wide, the 92%-lit disk
of Venus 11 wide.
On this same big evening, the trio of
Venus, Jupiter, and Mercury t within
their smallest circle of sky, just over 5 in
diameter. Venus and Jupiter remain 2
Looking South Looking South-Southwest
apart or less from August 25th to 29th.

46 August 2016 sky & telescope

To nd out whats visible in the sky from your location, go to skypub.com/almanac. Fred Schaaf

December
solstice

O R B IT S O F THE P L ANE T S
The curved arrows show each planets movement March Sept.
Sun
during August. The outer planets dont change equinox equinox
Venus
position enough in a month to notice at this scale.
Mercury Earth

June solstice Mars

EVENING
Mars and Saturn, together with Antares,
put on a rare and beautiful show in
August and its easy to see.
Mars spends the month dimming Jupiter Uranus
from magnitude 0.8 to 0.3 and shrink-
ing from 13 to 10 wide. But thats still Saturn Neptune
big and bright enough to display well the
campre color of Mars to the naked eye
and potentially some surface features in Pluto
the telescope.
Saturn, though dimming from
magnitude +0.3 to +0.5 over the course
of August and getting a bit smaller, still
shows its rings far open in telescopes. from Libra to Scorpius and then, around and Antares, as August ends. By August
Both Mars and Saturn transit roughly August 9th, passes very close to the south 31st, both planets set at approximately
around sunset, so get your scope on them of the bright and unpredictable variable 11:30 p.m. daylight-saving time.
right at dusk before they sink lower. star Delta () Scorpii. The most amazing
The real drama, however, comes from views come on the American evenings of NIGHT
Marss march into and through upper August 23rd and 24th, when Mars travels Pluto spends the month of August in the
Scorpius. As August starts, Mars crosses between Saturn and Antares. On both Sagittarius Teaspoon. The dwarf planet is
evenings Mars appears less than 2 north observable with a large-aperture telescope
of Antares and a bit more than 4 south of most of the night but is highest in late
Dawn, Aug 24 26
Saturn. Although Antares, at an average evening; see the July issue, page 48, for a
1 hour before sunrise Pleiades
magnitude of +1.0, shines 1.4 magnitudes nder chart.
Moon dimmer than Mars (less than a third as Neptune, in Aquarius, reaches oppo-
Aug 24
bright), their colors are comparable. sition on September 2nd, so its already
Mars zooms east, away from Saturn visible almost all night. Its at its highest
Hyades TA U R U S soon after midnight. See skyandtelescope
.com/urnep for nder charts for both
Aldebaran Dusk, Aug 27
Moon Neptune and Uranus, which rises a few
Aug 25 45 minutes after sunset
hours after sunset in Pisces.

Moon MOON PA SSAGES

Aug 26 The slender crescent Moon poses very
low near Venus, Mercury, and Jupiter at
dusk on August 4th and a bit higher near
Less than
Denebola Jupiter on the 5th. The gibbous Moon
1: apart!
2 forms a large but dramatic equilateral
Betelgeuse ORION triangle with Mars and Saturn at night-
fall on August 11th. On August 25th, the
Venus Moon occults Aldebaran for much of
Jupiter
Rigel the eastern and southern United States
Looking Southeast, high up Looking West (including Hawaii) and central America;
see page 51.

Sk yandTelescope.com August 2016 47

OBSERVING
Celestial Calendar

Perseids to Get a Jupiter Boost?

After the Moon sets, the Perseid meteors could be unusually rich.

BRAD GOLDPAINTIC

The most-observed meteor shower is In a normal year, you may see about shower can vary a lot from year to year.
the annual Perseid display, active for sev- 60 to 90 Perseids per hour on the peak And this years shower will prob-
eral nights in prime vacation season. This night between midnight and dawn if ably be better than usual. Theres even a
year the Moon will be waxing gibbous on you have an excellent dark sky. But the chance that it could be spectacular.
the predicted peak night, August 1112.
Four hours, compressed. I created a composite of all the meteors captured on August 13, 2015,
But the Moon will set around 1 a.m. for
from 12:30 to 4:30 a.m., writes Brad Goldpaint from northern California. The large mountain in
mid-northern observers, leaving the night the distance is Mount Shasta, and the glow from the base of the mountain is the city of Mount
dark for the three or four prime meteor- Shasta. The evening before, he recorded the starry sky and its reection in the still lake in a
watching hours before dawn: this is when 25-second exposure. The landscape is from a long exposure he shot at a very low ISO during deep
your side of the Earth faces most directly twilight. He took dozens of sky exposures during the morning hours, subtracted out the 65 mete-
into the oncoming meteoroids. ors that these recorded, and aligned them to their star backgrounds in the original sky image.

48 August 2016 sky & telescope

Joe Rao, a seven-time Emmy-nominated broadcast meteorologist at News 12 in Westchester, N.Y., has been an assidu-
ous amateur astronomer for nearly 50 years. He won the Astronomical Leagues Walter Scott Houston Award in 2009 Joe Rao

An Enigmatic Enhancement So what caused the high rates in 1980? after sunrise for North America, but peak
For the last several years, the Perseids It was probably a completely unrelated activity usually lasts about 24 hours.
have been quite normal. But in the late perturbing inuence by the most mas- Maslov points out that in addition,
1970s and early 1980s the shower turned sive planet: Jupiter. fresh debris trails shed by Swift-Tuttle in
unusually active. The 1980 display was The rst to formally propose that 1479 and 1862 (fresh implies dense and
one of the best in memory up to then; Jupiter plays a role in Perseid activity narrow) will likely encounter Earth and
many observers reported seeing more were Esko Lyytinen of Finland and Tom might also provide a brief enhancement
than 120 per hour and occasionally up Van Flandern of the U.S. Naval Observa- of activity. Eastern Europe and western
to 5 or 6 a minute. A reputable Japanese tory, in 2004. The comet passes a good Asia are in the best position to watch for
observer counted nearly 250 in one hour. 1.7 a.u. above Jupiters orbit while moving this, as it should happen during their
The Perseid meteoroids are dusty inbound toward the Sun. But because the early-morning hours when the Perseid
debris bits shed by the periodic comet comet and the meteoroid stream all radiant is highest.
109P/Swift-Tuttle, which was discovered along its orbit have made hundreds of Moreover, French meteor expert Jr-
in the summer of 1862. Many experts in trips around the Sun over tens of thou- mie Vaubaillon has calculated an older
the 19th and 20th centuries calculated sands of years, slight periodic perturba- discrete trail of the comets rubble dating
its orbital period to be 120 2 years, and tions can add up. back to 1079. He forecasts Earth pass-
summer 1981 was considered the most Every 11.86 years (Jupiters sidereal ing closest to the middle of this trail at
probable time for the comet to be recov- period), Jupiter passes under the broad 4:56 UT August 12th, which would favor
ered. Meteoroids tend to be thicker in the rubble stream. Each time, its gravita- eastern North America on top of whatever
vicinity of their parent comet, so astrono- tional eld shifts some of the comet dross else is happening. This might lead to a
mers naturally assumed that the strong about 0.01 a.u. closer to passing Earths sudden outburst of bright meteors, but
Perseid activity in 1980 was due to the orbit. This segment of dusty debris takes Vaubaillon cautions, This 1079 trail [is]
impending arrival of Swift-Tuttle. about 16 more months to reach our path, quite old, making the forecasting less
Yet the comet failed to appear during whether Earth happens to be there or certain. I certainly would look for it, but
its anticipated 19791983 time frame. Per- not. The long-term result: when Earth just keep in mind the uncertainties.
seid activity through the 1980s returned reaches the Perseid-intersecting part of As always, the rates you actually see
to normal, and many assumed that its orbit in mid-August, occasionally an are less than the ZHR unless the radi-
Comet Swift-Tuttle which had evolved extra stream of Perseids will be passing ant (in northern Perseus) is overhead
into a strikingly beautiful object after its through at the same time. and your sky is dark enough for magni-
1862 discovery had somehow slipped If this happens about every 12 years in tude-6.5 stars to be visible. Light pollution
by undetected. sync with Jupiters orbital period, we have reduces the numbers, though the bright-
The late Brian G. Marsden, longtime a nice explanation for not only the strong est ones will shine through. The meteors
director of the Minor Planet Center 1980 display, but also the enhanced themselves ash into view anywhere in
(MPC) at the Harvard-Smithsonian Cen- showers that were reported in 2004, 1968, the sky, not necessarily near the radiant.
ter for Astrophysics, put forward an alter- 1945, and 1921. To do a meaningful meteor count by
native solution: that Comet Swift-Tuttle standard methods, so that your count can
was perhaps identical with a comet briey What About 2016? be integrated with others made all over
seen in 1737. If so, it might still return. . . This would appear to be another of those the world for many days running, see
around 1992. prime years. Russian meteor expert imo.net/visual/major. There too you will
Few astronomers believed it. Hadnt Mikhail Maslov, who has closely studied nd the required forms for submitting a
the Perseids ramped up around just the the evolution of the Perseid stream in report of your count.
right time? The legendary astronomy space, predicts a signicant increase Good luck and clear skies to all!
popularizer Sir Patrick Moore pooh- of Perseid background activity, with a Joe Rao
poohed the idea that Swift-Tuttle would zenithal hourly rate (ZHR) of 150160.
reappear in 1992 and bet a colleague a By comparison, last years Perseid shower
bottle of whiskey that it wouldnt. reached a peak ZHR of about 90, judging FOLLOW THE SHOWER ONLINE:
He lost. The comet indeed returned from the counts submitted to the Inter- As meteor observers report their counts
in the fall of 1992, validating Marsdens national Meteor Organization (IMO) by to the IMO, you can watch this years
prediction. And the Perseids in the years observers worldwide. Perseid activity curve develop hour by
around then were even more memorably The showers predicted time of maxi- hour at imo.net.
abundant. mum is 12:40 UT August 12th. Thats

Sk yandTelescope.com August 2016 49

OBSERVING
Celestial Calendar

Resolve a Stars Disk Naked-Eye!

Stars are points. You learned that as treated to a naked-eye reappearance of because without high magnication,
soon as you took up astronomy. Theyre Aldebaran from behind the dark side of the the glare of the Moons sunlit terrain
so far away, with apparent diameters so waning crescent Moon. The crescent will hides even a 1st-magnitude star right
tiny (not counting the Sun, of course), be 23% sunlit. Observers near the graze line next to it. Aldebarans reappearance on
that theyre indistinguishable from how on the map at right have a chance to see a the dark limb will be much easier if
mathematical point sources would look, gradual occultation. For observers farther youre watching at the right moment!
even in the largest telescopes. north, the Moon and Aldebaran will per- Here are some times:
Well, most of the time. Various form a near miss. At Austin, the disappearance is at
technologies and techniques can now get Youll need at least a small telescope if 4:39 a.m. CDT, the reappearance at 5:19
around that stricture to some extent. But youre on the eastern side of the continent, a.m. CDT; Atlanta, d. 5:48 a.m., r. 6:40
for amateurs? Never! or in southern or central Europe, because a.m. EDT; Miami, d. 5:33 a.m., r. 6:43
Except in one instance: during a graz- there the occultation happens in daylight. a.m. EDT; Pittsburgh, d. 6:11 a.m., r.
ing lunar occultation of a bright red or The farther west you are, the darker the sky 6:44 a.m. EDT; Washington, DC, d.
orange star in particular Aldebaran, will be. Right along the graze line, the map 6:05 a.m., r. 6:53 a.m. EDT; Boston, d:
the 1st-magnitude eye of Taurus. indicates where the graze happens in day- 6:20 a.m. EDT, r. 7:03 a.m. EDT.
Aldebaran is not only the brightest star time, bright dawn, deep dawn, or night. More precise times, and additional
that the Moon can ever occult, its also Where the occultation is total rather than details including the altitudes of the
one of the largest in apparent diameter: grazing, you can also catch the stars disap- Sun and the Moon, are listed for over
20 milliarcseconds. If youre positioned to pearance on the Moons bright limb. For 1,000 cities and towns in the predic-
see the Moons edge barely skim Aldeba- this youll need a telescope even at night, tions link at the end of this article.
ran, you may witness it fading and reap-
When the Moons limb grazed Aldebaran over dz , Poland on April 28, 1998, Ladislav Smelcer
pearing less than instantaneously. Even
was there videorecording with an 11-inch Schmidt-Cassegrain scope. Here is every 5th frame of
with your naked eyes. a 3-second clip from his movie. Aldebaran dims gradually, rebrightens partially, then fades out
On Friday morning July 29th, observ- altogether. His setup inserted the date and local time into each frame; Universal Time is two hours
ers in much of the southern U.S. as well earlier (so the UT minute is 18:59). Twenty-ve other observers timed graze events visually, mostly
as Mexico and Central America will be by voice calls into tape recorders. In all, 142 contacts were timed.

LADISLAV SMELCER / DAVID DUNHAM/ IOTA

50 August 2016 sky & telescope

David Dunham, a founder of IOTA, has led the coordination of occultation
timings since 1962. Write him at dunham@starpower.net. David Dunham
Occultation of Aldebaran
July 29, 2016
fter
ze a
Gra unrise
The Graze s
Montreal
The most interesting views will be from Toronto
a strip of land only a few hundred yards N
No t
gh
occu
occu
oc ult
ltat
atiio
at ion
ion
occultation Bri wn
wide along the occultations northern da Fort
limit. You can examine the precise graze ep
De wn St. Wayne
path to street-level accuracy using the da Louis
interactive Google Maps link in the spe- Tulsa
ing
dur Oklahoma Occultation

S&T: LEAH TISCIONE, DATA: IOTA

cial page weve set up for this event, also z e t
Gra nigh Lubbock City visible
given at the end of the article. El Paso
Viewed from this narrow zone, the
giant star should disappear and reappear
multiple times as hills and valleys along
the Moons northern limb cover and
expose it. Most of these events will appear Observers in the southern and eastern US, the Caribbean, and most of Mexico can watch
non-instantaneous, even taking up to the Moon occult Aldebaran on the morning of July 29th. Along the graze line, youre likely
a full second, due to Aldebarans angu- to see gradual events due to the stars relatively large angular size. The graze occurs dur-
lar size: 40 meters wide at the Moons ing night for Texas, dawn from Oklahoma to Lake Erie, and daytime northeast from there.
distance. Sometimes a sideways-speeding
hill may cover only a part of the stars face, A Blue-Sky Aldebaran Occultation on August 25th
causing an incomplete partial occultation. One lunar month after the July 29th limb and the reappearance on the
We can now predict these narrow zones occultation, the Moon crosses Aldebaran dark limb. Some times: at Kansas City,
very accurately, thanks to the laser altim- again: during daytime on August 25th for disappearance 12:56, reappearance 1:11
eters on Japans Kaguya and NASAs Lunar much of the southwestern U.S. p.m. CDT; Denver, d. 11:43, r. 12:14 p.m.
Reconnaissance Orbiter spacecraft. These This time the Moon will be last quarter. MDT; Los Angeles, d. 10:21, r. 11:26 a.m.
mapped all of the Moons topography to Once again, because the Moon is waning, PDT; Berkeley, d. 10:17, r. 11:15 a.m. PDT;
high accuracy. So now, you can choose the disappearance happens on the bright Honolulu, d. 5:52, r. 7:17 a.m. HAST.
your viewing location to within just a few
meters in order to maximize the number
of contact events you can view or record. of the Hyades stars to be occulted on the Cincinnati, Ohio, and Ithaca, New York.
See the web page for the event. same night are. Again, see the web page. Details are in the event link.
From the mid-1960s into the 1980s, Even though we dont expect to learn Also to be occulted for various parts
observers with the International Occulta- much new from it, the July 29th Aldeba- of North America are several other stars,
tion Timing Association (IOTA) recorded ran graze is probably the best of the including the pair Theta1 and Theta2
hundreds of grazes, mostly visually, to current series for populous parts of North Tauri, magnitudes 3.8 and 3.4, respec-
rene the lunar prole and star posi- America. For that reason, IOTA will hold tively. Detailed predictions for those two
tions. Now that we know both of these its annual meeting in nearby Stillwater, are in the predictions link.
parameters very well, such observations Oklahoma, the weekend after the Friday-
are less valuable to astronomers. So since night graze; details are in the link. Most For More Information
the early 1990s, IOTA has concentrated its attendees will try to observe the graze We at IOTA have set up a special web
eorts more on asteroid occultations. from northeast of Edmond, Oklahoma; page for the July 29th event, with an
But lunar occultations do remain valu- some will be ready to travel if clouds interactive Google Map and much other
able to discover and resolve close double threaten. Youre welcome to join our expe- information: occultations.org/Aldebaran.
stars, especially when recorded with dition, the IOTA meeting, or both. Detailed predictions for most of the
video. The Kepler-2 Project is currently events mentioned here are listed for more
looking for exoplanet transits of stars Hyades Stars than 1,000 locations at lunar-occultations.
near the ecliptic. The Kepler team is very About two hours before Aldebaran reap- com/iota/bstar/bstar.htm. Note that the
interested in which of their program stars pears from behind the Moons dark limb, page for each star displays three long
might be close doubles, because stellar the 4.8-magnitude Hyades star ZC 677 tables with less-than-obvious divides: the
duplicity throws o the analysis of any will do the same for much of the eastern disappearance, the reappearance, and the
sign of an exoplanet. Aldebaran isnt suit- US. Its graze line will run about 100 locations of cities.
able for this particular work, but some miles south of Aldebarans and pass over David Dunham

Sk yandTelescope.com August 2016 51

 OBSERVING
Exploring the Moon

Twin Basins with a Twist

Track down two big basins one obvious and the other nearly invisible.

When looking through a telescope at the Moon, you see Its important to note that Grimaldi is not a crater but
the cumulative eect of 4 billion years of stu happen- rather a basin (an impact site having two or more rims).
ing. Some big features from long ago for example, Its large (460-km-wide) and more subtle outer rim is
Montes Apenninus, the towering mountain chain cre- dicult to see in images, but its red coloration makes it
ated during the Imbrium basins excavation 3.8 billion stand out in a gravity map. Technically, Grimaldis lava-
years ago are still clearly visible. But other features, covered oor could have been named Mare Grimaldis.
even sizeable ones, have vanished from view due to sub- Immediately to its south is another gravity bulls eye
sequent volcanism and impact erosion. of nearly the same size. It too must mark the site of a
Fortunately, as I described in Februarys issue (p. 48), basin and yet theres no obvious evidence for one on
precision mapping of the pull of lunar gravity by the the surface. Lunar geologists call this hidden feature the
twin Gravity Recovery and Interior Laboratory (GRAIL) Crger-Sirsalis basin (CSB), named for two craters that
spacecraft can reveal subsurface evidence of hidden it spans. Crger, 46 km across, is the lava-oored crater
landforms. In particular, impact basins produce the near the basins center, and Sirsalis is the brighter of
largest gravity anomalies on the Moon, typically with a two overlapping craters to the northeast. Based on their
central gravity high or mascon (mass concentration), high-low gravity signature, CSBs phantom rims have
surrounded by a ring of gravity lows. These appear as diameters of about 240 and 400 km.
blues and reds, respectively, in the map below. The high CSBs center is a patch of relatively at terrain with
in a basins center results from the rise of dense mantle few large craters. Usually the most visible parts of a
material under the basin and from dense mare lavas basin are its rims, but none exist for CSB. Their disap-
that partially ll its oor. The low corresponds to a thick pearance is probably related to the location of the basin
annulus of less-dense crustal material. near the younger and larger Orientale basin. The latters
Thats the pattern underlying the Orientale impact ejecta swept across this area, knocking down and cover-
basin, which barely peeks around the Moons western ing preexisting terrain with torrents of debris. Grimaldi
limb. Nearby are two smaller red-around-blue gravity basin is about the same distance from Orientale, and yet
signatures of basins. The northern bulls eye is asso- more of its rim structure remains. Perhaps CSB predates
ciated with the Grimaldi basin, whose 220-km-wide Grimaldi, such that its surface features had already been
mascon is about the same diameter as the distinct rim degraded when the Orientale impact occurred. Interest-
that surrounds its central plain of dark lava. ingly, the centers of CSB and Grimaldi are both 1 to 1 km

NASAs GRAIL
mission mapped
in detail where
the lunar gravity Grimaldi
eld is locally
stronger (blues)
or weaker (reds)
and its global Crger-
map reveals the Sirsalis
distinct bulls- Orientale
eye signatures
that underlie Humorum
impact basins.
NASA / LRO / GRAIL

300 km

52 August 2016 sky & telescope

Visit Contributing Editor Charles A. Woods Lunar Picture of the Day website at www2.lpod.org. Charles A. Wood

The Crger-
OCEANUS
PROCELLARUM Sirsalis impact
basin, south of
Grimaldi along
the Moons
western limb,
Grimaldi
shows no
rims. Yet its
gravity signa-
ture (center)
Sirsalis
and telltale
Rocca A patches of
mare lava seen
Lacus
is

near full Moon

al

Aestatis
rs

(right) conrm
Si

its reality.
a
m

Crger

NASA / LRO / GRAIL (3)

Ri

Darwin
De Vico A

lower in elevation than the surrounding topography so beneath that lumpy surface might be a 240-km-wide
basin depressions can remain after their rims disappear. plain of lava ows, some of which escaped to the surface
This hidden basin explains why youll see small at Crger, Lacus Aestatis, and on the oor of Rocca A
patches of mare lava in Crger, Lacus Aestatis, and (northwest of Crger). The large crater Darwin and
nearby at full Moon. All of these ows lie within the other unnamed ruined craters occupy the space where
inner rim of CSB, having leaked onto the surface because the gravity map shows the red zone of low-density crust.
the crust is thin and penetrated by impact-induced faults All these dierent data sets gravity, topography, and
that provided conduits from magma reservoirs below. imagery peel back layers of the complex history of this
Gravity data also provide a clue to another mystery. corner of the Moon. The surface is just the starting point
Rima Sirsalis is a straight rille that has a surprisingly for understanding everything thats occurred. So take
big bend near the crater De Vico A. GRAILs map shows your time and imagine what might lie deeper down.
that the bend occurs exactly where the rille, if it had
maintained a straight course, would have cut through
The Moon August 2016
the boundary between the basin mascon and the sur-
rounding crustal rocks. So perhaps a sharp subsurface 24
transition related to the basin created the rilles elbow. Phases
If you want to take your personal exploration of the NEW MOON
Moon beneath its surface, the Grimaldi and CSB areas are August 2, 20:45 UT
Grimaldi
good places to learn. Look when the libration is favorable, FIRST QUARTER
as it will be during full Moon on August 18th and for a few August 10, 18:21 UT 6
days thereafter. Grimaldis dark lavas are easy to spot, as
NASA / LRO

FULL MOON 14
are the surviving segments of the rim that encircles them. August 18, 9:27 UT
Then look closely for a lower-lying zone of relatively LAST QUARTER For key dates, yellow dots indicate which part
smooth material just outside the basins southern rim. August 25, 3:41 UT of the Moons limb is tipped the most toward
This is a moat between the inner rim and the outer Earth by libration under favorable illumination.
one, seen not as a circle of hills but rather marked by a
Distances Favorable Librations
decrease in elevation. The corresponding moat and outer
rim are nearly invisible on the basins northern side. Apogee August 10, 0h UT Mare Smythii August 6
Now imagine what once must have existed at CSB. 404,262 km diam. 29 34
Cabeus (crater) August 14
The center of this lost basin lies just north of easy-to-spot Perigee August 22, 1h UT
Crger. Notice that this central area is relatively at and 367,050 km diam. 32 34 Hermite (crater) August 24
sprinkled with hills of Orientale ejecta. Tens of meters

Sk yandTelescope.com August 2016 53

OBSERVING
Deep-Sky Wonders

Scutums Gems
Part the misty vapors of the Milky Way
to nd these glorious objects.

Without a doubt, the shining jewel of the constellation

Scutum is the open cluster Messier 11, also known as
the Wild Duck Cluster. German astronomer Gottfried M11
Kirch discovered it on September 1, 1681. At rst he was A good number of M11s
uncertain whether he was seeing a comet or a nebu- stars can be resolved with
lous star, but he dismissed the possibility of it being a a medium-aperture scope
comet when the objects position remained unchanged at high power. The author
during succeeding nights. More than half a century sketched the cluster as
later, British cleric and astronomer William Derham viewed through her 130-
published his observations of nebulous stars, which he mm refractor at 164.
called whitish Are, like a Collection of Misty Vapours:
whence they have their Name. In the same memoir, diameter. The stars are all 11th magnitude except one
Derham became the rst observer to report that he 9th magnitude . . . [and] it is broken into 5 or 6 distinct
Star magnitudes

4
5 found Kirchs object to be a cluster of stars. groups with rifts or cracks between them. A glorious
6 Perhaps the historical description that resonates most object. To me, M11 looks as though a crystalline star
7
with me is one recorded by John Herschel in his 1833 was dropped on the obsidian oor of the night, its many
8
catalog: A beautiful irregularly round cluster 10 or 12 shattered fragments outshone by a small remnant of

60 2
19h 00m 18h 50m 18h 40m 18h 30m
AQUILA

7 SERPENS
8
CAUDA
14 The NGC 6704
15 Tr 35 4
Bracelet
Sh 2-61
6704
6682
HD 174208 R
12 Apriamaswili 1 6
M11

SCUTUM

M26
10

M11

12
UY NGC 6704 lies just over 1 north of open cluster M11.
The Barnard 111 complex of dark, or absorption, nebulae
stretches between and around the two clusters.

SCOTT ROSEN

54 August 2016 sky & telescope

Sue French welcomes your comments at scfrench@nycap.rr.com. Sue French

its core. Ive tried to portray M11 as seen through my at 164 it displays about 15 faint to very faint stars over
130-mm refractor at 164 (facing page), but the dusky a patchy mist of unresolved stars. Its roughly 5 across
ssures splitting its rafts of stars are best captured with and more concentrated in the center. My 10-inch reec-
your own eye. No image or sketch can truly do justice to tor at 166 plucks out 40 stars gathered into an odd shape
this magnicent cluster. covering 6. A dense clump of stars dominates the center,
M11 is also the bauble decorating the Bracelet, an with a sparse scattering of stars to its south, as though
asterism that Arizona amateur Bill Dellinges noticed some trickled out of the main mass. A starry band reaches
with 750 binoculars. Dellinges says that the Bracelet is westward from the clump, and from its end, a sweeping
one of those shapes that, once imagined, you can never
again fail to see. Through my husbands 742 binoculars,
its easy to imagine an open-ended bracelet. It starts at
14 Aquilae and then curves through the stars 15, Lambda
AQUILA
(), and 12. The Bracelet then crosses over into Scutum
with Eta () Scuti and proceeds through the stars HD
174208 and Beta (). Finally it returns to Aquila, ending
at the star pair 7 and 8 Aquilae. All but three are mag-
nitude 5.4 or brighter, so stargazers blessed with dark
skies may be able to see most of the asterism with the
unaided eye. When R Scuti is near maximum light, it
adds another star to the bracelet.
A lesser gem on the bracelet is Apriamaswili 1, dis-
covered by S. P. Apriamasvili of the Abastumani Obser-
vatory in 1964. The rst spelling is the objects name
as listed in the Simbad Astronomical Database, and the
second is the authors name as youll nd on the discov-
ery paper in the SAO/NASA Astrophysics Data System.
SCUTUM
Confusing matters further, some journal papers by the
same astronomer are found under the name Apriamash-
vili. We owe these dierences to various transliterations
The small constellation
of a name written in Georgian script. The cluster is
Scutum, the Shield, stretches
often called Basel 1, a later name bestowed in 1970. across the Milky Way to meet
Apriamaswili 1 is boxed up in a 35 13 trapezoid Aquila in the east.

PK CHEN
formed by four bright stars. My 130-mm scope at 48
shows a little knot of several faint stars and haze, which
at 102 breaks up into 18 faint to very faint stars loosely The Jeweled Shield
tossed across 5 of sky. Through my 10-inch reector at
68, the delicate cluster becomes a fairly conspicuous Object Type Mag(v) Size/Sep RA Dec.
bunch of at least 20 stars, magnitude 11 and fainter. A Messier 11 Open cluster 5.8 11 18h 51.1m 06 16
magnication of 115 makes it clear that the group has
an irregular shape, as well as indenite borders. Strag- Bracelet Asterism 4.8 2.6 18h 56.5m 04 39
glers seem to expand the group to 7 and 30 stars. Apriamaswili 1 Open cluster 8.9 5.5 18h 48.1m 05 51
Lets turn our attention to the open cluster NGC
NGC 6704 Open cluster 9.2 5.0 18h 50.8m 05 12
6704, discovered by the outstanding German astrono-
mer and comet-hunter Friedrich August Theodor Trumpler 35 Open cluster 9.2 6.0 18h 43.0m 04 14
Winnecke with his 3-inch Mertz comet seeker in 1854. NGC 6682 Star cloud 47 18h 39.6m 04 46
Through the small refractor he saw it as a faint nebula,
but when he later viewed it with the 9.6-inch refractor at Sharpless 2-61 Emission nebula 2.0 18h 33.4m 04 58
the observatory in Berlin, he found that it was a coarse UY Scuti Red supergiant 8.610.5 18h 27.6m 12 28
cluster of stars.
Angular sizes and separations are from recent catalogs. Visually, an objects size is often smaller
NGC 6704 sits 1.1 north of M11 within a oval of than the cataloged value and varies according to the aperture and magnication of the viewing
stars, 8.6 magnitude and fainter. The cluster looks like a instrument. Right ascension and declination are for equinox 2000.0.
granular haze through the 130-mm refractor at 48, while

Sk yandTelescope.com August 2016 55

OBSERVING
Deep-Sky Wonders

Sh 2-61

POSS-II / CALTECH / STSCI / PALOMAR OBSERVATORY

curve of moderately bright stars arcs around to the north, The nearly inscrutable emission nebula Sharpless 2-61 rests at
evocative of the graceful arm of a spiral galaxy. the center of this 3015 arcminute eld. Sh 2-61 is a compact
Hopping 1.2 west-northwest from Beta Scuti takes H II region ionized by a multiple star system.
us to the open cluster Trumpler 35, which stands out
rather well as a patch of haze sprinkled with fairly faint For our nal visit, lets plunge much farther south
to very faint stars when viewed through my 130-mm to the semi-regular variable star UY Scuti, a pulsating
scope at 48. At 102 I see at least 20 stars in a 6 group, red supergiant with a period of roughly 750 days and a
the brightest ones forming an arc thats concave toward visual-magnitude range of 8.6 to 10.5. However, thats
the northeast. The 10-inch scope reveals about 35 stars, not where its attraction lies. UY Sct is a leading can-
12th magnitude and fainter, many in radial chains that didate for the title of largest known star, even though
stretch the group to 8 across its longest dimension. uncertainties in size determinations for red supergiants
If we slip 1 west-southwest from Trumpler 35, well are great enough to blur the ranking among them. In
encounter an absorption hole a thinning of interstel- the June 2013 issue of Astronomy & Astrophysics, Beln
lar material that absorbs light from background stars. Arroyo Torres and colleagues determined the mean
Here we see the star cloud NGC 6682, a pileup of radius of the star to be 1,708 (plus or minus 192) times
remote suns beheld through this relatively clear win- the radius of our Sun. If you replaced our Sun with UY
dow. The 130-mm refractor at 28 nicely shows o this Sct, the stars outer surface would extend more than
-wide enhanced splotch of Milky Way peppered with halfway between the orbits of Jupiter and Saturn.
faint stars. Two bright stars, magnitude 7 and 8, rest just Red supergiants are quite distended, and UY Sct
o the west and northeast edges, respectively. weighs in somewhere between 25 and 40 times the mass
The emission nebulae Sharpless 2-61 resides 1.1 of our Sun. The star is sometimes referred to as a hyper-
west of the 7th-magnitude star near NGC 6682s edge. giant, but this is a misnomer. Technically, hypergiant
In my 130-mm scope at 102, its a small, faint glow with stars have a luminosity class of 0, while UY Sct is Ia, the
a dim star embedded. Nebula lters dont signicantly highest luminosity class for supergiants.
improve the view. With the 10-inch scope at 166 the When I looked at UY Sct with my 130-mm refractor
nebula spans about 1. The star sits north of the nebu- at 37, it was near maximum brightness and smoldered
las center, and a few fainter stars are superimposed. The with a deep red-orange hue. It reddens more as it dims,
embedded star is actually a multiple system with several but you may need a larger scope to detect the color. Id
tightly spaced components that likely belong to a youth- like to thank fellow astronomy club member Greg Now-
ful star cluster enshrouded by its nebula. ell for bringing this fascinating star to my attention.

56 August 2016 sky & telescope

THE GREAT AMERICAN ECLIPSE
NASHVILLE, TN AUGUST 17 21, 2017

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Join Sky & Telescope for The Great American Eclipse Stassun is Profes-
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at
a Vanderbilt University,
sor
s of Physics and As-
of August 1721, 2017. Based amidst the many attractions tronomy
t at Vanderbilt
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w he also directs
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p in the Com-
of Nashville, Tennessee, we plan to view the eclipse near the point University.
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of greatest eclipse (see also the green GE drop pin below) near his
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Hopkinsville, Kentucky. From the Oregon desert to the Carolina coast, Foundation
F Graduate
Scientic Computing. He earned his bachelors
weve scrutinized the data and factors for viewing sites. Clear skies, degree in Physics and Astronomy at Yale in 1980
Research Fellow at the University of Wisconsin,
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duration, maneuverability, remoteness, and potential activities are all Madison. He was a postdoctoral research
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part of the equation, and Hopkinsville is a terric all-around location. Program before joining the faculty at Vanderbilt.
the Vanderbilt Astronomy faculty in 1991. In
20112012, he served as Chair of the University
Professor Stassuns research on the birth of
Ofcial kickoff is August 17, 2017, in Nashville, Tennessee. In vacation stars, eclipsing binary stars, exoplanetary
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ShadesofCyan
 S & T Test Report Rod Mollise

Space-Walking
with the Meade MWAs
These new 100 eyepieces oer users vast elds and good ergonomics.

ROD MOLLISE

Im addicted to that space walk- also determines how much actual sky, how much The Mega Wide
ing experience observing the sky through true eld, is shown. Eyepieces each
ultra-wide-angle eyepieces with large apparent I began my love aair with large AFOV ocu- feature a vast
elds of view (AFOV). When Im using a large lars in the early 1990s after I got a look through apparent eld of
AFOV eyepiece, its like Im oating in space with a Tele Vue Nagler eyepiece. Its 82 apparent eld view in a comfort-
no telescope between me and the sky. The eld forever spoiled my 55 Plssls for me. About able housing that
does not interfere
circle in the eyepiece is huge and the view much seven years ago, things got even more serious
with your eye
more absorbing than in an ocular with a nar- when 100 eyepiece designs entered the market.
placement.
rower apparent eld. Expressed in degrees, AFOV Suddenly, the 82 eyepieces I loved didnt seem as

58 August 2016 sky & telescope

 WHAT WE LIKE:
Generous eld of view
Comfortable design
Meade Series
5000 Mega Wide
WHAT WE DONT LIKE:
Angle Eyepieces
Rubber eyecups wouldnt
U.S. price: $199.95 to $249.95
stay put
Available from Meade.com and
dealers worldwide

special anymore. So, did I go out and replace all my ocu- Eye relief is the distance you need to position your
lars with 100 wonders? No. There was a problem: cost. eye from an eyepiece to take in the entire eld of view.
Ultra-wide eyepieces were priced at $600 and up, Meade gives eye relief gures of 20 mm for the 21- and
which kept my inventory down to two. That could 15-mm eyepieces, 19.7 mm for the 10-mm, and 13 mm
change now, however, with the introduction of the for the 5-mm ocular, and my measurements conrmed
modestly priced Series 5000 Mega Wide Angle (MWA) they were correct. Even 20 mm is not much eye relief
eyepieces from Meade. for those who wear glasses while observing, but its still
fairly generous for ultra-wide-eld oculars.
General Overview To roughly determine the MWAs apparent elds, I
The MWA series consists of four eyepieces with focal timed how long it took a star near the celestial equator
lengths of 21, 15, 10, and 5 mm. While it would be nice to cross the eld in an undriven scope. I then converted
to have an ocular with a longer focal length than 21 that gure to AFOV. The three oculars with longer focal
mm, its not as necessary with 100 eyepieces as with lengths were close to Meades 100 specication. Only
narrower ones. The 21-mm covers a large true eld and the 5-mm came up a little short at about 94.
is actually a better performer in light pollution than I also checked for pincushion and barrel distortion,
a lower-magnication eyepiece, tending to spread out though slewing around dense star elds, which revealed
background sky glow. little evidence of either problem to my eyes.
When using multiple eyepieces, optics are only part Meade also claims the MWA series are parfocal,
of the story. Equally important are their mechanical meaning that they reach focus at the same point. Thats
characteristics, not just for durabilitys sake, but for
ergonomics. If its dicult to properly position your eye
at the eyepiece, it doesnt matter how good the glass is.
The MWAs look modern, but unlike some oculars, their
barrels dont get in the way of proper eye placement.
The Mega Wides are equipped with rubber grip rings
and feel good in your hand. Their nish is outstanding,
and removing the caps from the eye and eld lenses
reveals perfect-looking greenish lens coatings (they are
fully multi-coated). All visible interior surfaces, particu-
larly the eye lens and eld lens areas, are well-blackened
to reduce light scatter. Each eyepiece is threaded to
accept standard lters.
Was there anything I didnt like about the MWAs
mechanics? Their rubber eyecups tended to become
detached. When I folded an eyecup up to block stray
light, it would often pop o and Id lose it in the grass on
ROD MOLLISE

a dark observing eld. But this is a minor quibble.

The rst thing I did after the MWAs arrived was
to check their two most important specications, eye
relief and apparent eld. While Meade publishes these Internal reections were well controlled in each of the MWA
specications in their promotional literature, my motto eyepieces, though the 21-mm required more care when positioning
is trust but verify. your eye to avoid kidney-bean blackouts of parts of the eld.

Sk yandTelescope.com August 2016 59

 S&T Test Report

not quite true in practice. The 21- and the 15-mm models 10-mm
are 2-inch eyepieces and are indeed parfocal with each Like the 15-mm, the
other, as were the 10- and 15-mm eyepieces. But the 10- 10-mm is perhaps a better
and 5-mm eyepieces have 1-inch barrels and must be balance of eld size and
used in an adapter, which usually places them farther optical quality than the
out in the telescopes focuser. As such, they dont focus 21-mm. Stars were small
at the same place as the 2-inch eyepieces. and well shaped at the
eld edge in my Schmidt-
21-mm Cassegrain, which made
This seven-element eye- star clusters look great.
piece is the most physically The 10-mm became my
imposing of the MWAs, glob buster, making
and is something of a short work of smaller
handful at 1.68 pounds. In globular star clusters like M92 in Hercules, deliver-
performance, the 21-mm ing plenty of tiny stars on a dark background. This one
was paradoxically the most weighs in at a fairly modest 14.7 ounces, and, like the
and least impressive of 15-mm, incorporates eight lens elements.
the set. Its huge eld was
breathtaking, but stars 5-mm
more than 80% of the way While the 5-mm came up
to the edge of the eyepiece a little short in the AFOV
looked misshapen in my f/5 Dobsonian reector. gure, it acquitted itself
Much of this was due to the star-distorting coma well in every other regard.
inherent in a short-focal-ratio telescope. When I added a Stars were better at the
coma corrector, star appearance improved considerably eld edge than in any of
across the eld, but some residual astigmatism in the the other MWAs. Perhaps
eyepiece design meant stars toward the edge were still the greatest compliment
not perfect. Unsurprisingly, edge-of-eld stars looked I can pay this ocular is to
better in my f/10 Schmidt-Cassegrain telescope. call it a good planetary eye-
I found it important to keep my eye close to the eye- piece. Saturn was beautiful
pieces optical axis. Move it to one side and performance in my Dobsonian at 250,
was poorer. Id get kidney-beaning, bean-shaped dark and its wide eld meant I didnt have to continually
patches in the eld of view, and also some spurious color nudge the scope along to track. This nine-lens-element
on bright objects. In practice, it was not hard to position eyepiece weighs only 11.8 ounces and handles like a
my eye properly and soon became second nature. normal eyepiece.
I thoroughly enjoyed observing with the MWAs, but
15-mm beyond the fun, there were a few surprises. The big-
While it doesnt oer the gest was how well they stacked up to my premium 100
space-spanning views of oculars in use. Stars at the edge of the eld were not as
the 21-mm, the 1.4-lb., good as in premium oculars, but even with the large,
15-mm MWA shows a nice low-power eld of the 21-mm that rarely bothered me.
wide swath of sky and its I was concentrating on the eyepiece center most of the
shorter focal length is less time, and only bright problem stars on the edge of the
demanding of the optical eld normally caught my attention. Still, when directly
design. Stars at the eld compared with the more expensive eyepieces, the MWAs
S&T: SEAN WALKER (4)

edge were respectably presented a slightly softer view overall.

round, both due to coma After my testing was done, I just had a ball space-
being less prominent walking with the Mega Wides. The MWAs are good
because of the 15s lower performers by any standard, and the fact that they dont
astigmatism and its higher magnication. Eye place- break the bank to deliver means I cant help but be
ment was also less critical than with the 21-mm. Despite enthusiastic about them.
the presence of eight lens elements (which could dim
the view by absorbing some light), objects seemed just as S&T Contributing Editor Rod Mollise loves the view through
bright as in other 15-mm eyepieces with fewer lenses. a quality eyepiece.

60 August 2016 sky & telescope

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62 August 2016 sky & telescope

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Sk yandTelescope.com August 2016 63

Jerry Oltion
Astronomer's Workbench

The Future is Fast

Phill Oltmanns 32 f/2.4 scope raises and lowers the bar.

on the same 18-point cell used in the nal telescope, to

ensure adequate support. An overhead arm held the tool
in place and dierential friction made the tool rotate
while polishing. Phill varied the tools oset every 15 to
20 minutes to avoid creating zones.
Grinding and polishing took only two months, but
parabolizing took one and a half years! Phill could only
work on it during the summer, and he could only put in
about three hours a day, using tools of 12, 10, and 6
diameter pushed by hand. He used Ronchi and Foucault
tests, going exclusively with the Foucault test and a 19-slot
Couder screen as he approached his desired parabola.
During the parabolizing phase he learned that the
amount of glass removed when transitioning from a
spheroid to a paraboloid increases exponentially with
decreasing f-ratio. Canadian optician Peter Cerovolo
began parabolizing one of his fast scopes during ne
grinding, and Phill says, Considering the extreme
amount of work I did guring the mirror, thats what I
Phill Oltmann with his 32-inch f/2.4 scope. The scope stays put
will do in the future if ever I lose my mind and try
while the observatory rolls away from it, using the same motor
that powered the polishing process. another such project.
One downside to large, fast telescopes: the secondary
mirror has to be big. Phills is 8.5 on the minor axis.
I have seen the future, and it is fast. Its Theres a hidden bonus, though: the extra length taken
also vast. Thirty-two inches in diameter, to be precise, up by the secondary cage diameter shortens the scopes
and less than seven feet high at the eyepiece. height. This scope wound up being shorter than his 20!
Modern telescope making seems to be a rush toward As Phill says, Its nice to have only one step up a ladder.
ever greater apertures at ever shorter focal lengths. He patterned the scopes OTA on David Kriege and
Alberta, Canada ATMer Phill Oltmann has pushed those Richard Berrys book, The Dobsonian Telescope, so it has
parameters about as far as Ive ever seen. Inspired by a distinct Obsession look to it. Its an Obsession seen
Mike Lockwoods 20 f/3, Phill decided to see how large in a funhouse mirror, though, with trusses less than
and fast he could go. He had already made a 20 f/4 and three feet long.
realized that if he used the same tools to generate the
same curve, he could make a 32 mirror at f/2.5.
He ordered a blank from Newport Glass and had them
pre-generate the rough curve, removing nearly 13/16 of
glass from the 2.5 blanks center. He began grinding
Parabolizing was
with 60-grit to remove the striations from the curve gen-
done by hand
erator, then graduated to ner and ner grits as with any
with 12, 10, and
other mirror. He did all the grinding by hand with the 16
PHILL OLTMANN (2)

6 tools, using
granite grinding tool hed used on his 20. mostly half-
For polishing he built a 24 dental plaster tool and diameter strokes.
motorized the mirror on a spindle. The mirror rested

64 August 2016 sky & telescope

 Join in

Iceland
O t b 2 to
October t 8,
8 201
2016
16
PHILL OLTMANN

Auroras, waterfalls,
the Golden Circle,
The f/2.4 mirror is so deep, friends called it
the soup bowl. Phill proves them right in the
and much more
photo above.

So after constructing this amazing

squat beast, how does it perform? In a
word: beautifully! I had the privilege to
look through this scope during a vacation
to the Arizona/New Mexico area where
Phill spends his winters, and I can attest
that the view is nothing short of spectacu- 800.688.8031
lar. Thanks to a 3 Paracorr, the stars are SkyandTelescope.com/iceland2016
ope com/
com//icel
celand2
land
d201
d 20
016
16
pinpoints from edge to edge of the eld, a AURORA OVER SELJALANDSFOSS / BABAK TAFRESHI

eld thats an impressive degree across in

a 17-mm Ethos eyepiece. And the image
is just as bright as youd expect for a 32
mirror. After looking at the Orion Nebula
with it, I just about fell over.
It wouldnt have been much of a fall.
Thats the beauty of this scope. As Phill
says, it provides all the amenities of a www.observa-dome.com
big scope with only one step up a ladder.
Truly, the super-fast Dobsonian is the As the countrys oldest dome manufacturer, Observa-DOME has developed
next stage of evolution in visual observa- unmatched expertise. No matter what the use, the climate, the installation,
tion and aperture fever. the design, or your location, Observa-DOME meets the challenge.
I couldnt agree more. NASA MCAT
Phill Oltmann would like to dedi- 7-Meter Fast Tracking Dome
cate this article to the memory of his Ascension Island

friend and mirror-making mentor,

Barry Arnold. Phill can be contacted at
dr.philloltmann@yahoo.com.

In his years grinding mirrors, Jerry Oltion

has gone as fast as f/3.8, which is rapidly
becoming pass.

Do you have a telescope or observing

accessory that S&Ts readers would
enjoy knowing about? Get featured in Rare Inventory-Reduction Sale
Astronomer's Workbench by e-mailing
Jerry Oltion at j.oltion@s.net. Phone (601) 982-3333 (800) 647-5364 371 Commerce Park Drive
Fax (601) 982-3335 mail@observa-dome.com Jackson, MS 39213

Sk yandTelescope.com August 2016 65

 Imaging Technique

Processing
with PixInsight
Follow this workow to get more
out of your deep-sky astrophotos.

FROM SCOPE Ron One size ts all is a rarely used PixInsight is perhaps the only software
TO PRINT PixInsight Brecher term in astrophotography. Astro- that can handle everything from basic image
is an all-encompassing imagers shoot all types of deep-sky calibration to advanced processing. It reads and
astronomical image- objects in a variety of ways: wide writes virtually every image le format and has
processing program eld or high magnication, color or eective tools for just about anything youd want
that runs on all major
monochrome, natural or repre- to make your images stand out from the crowd.
computer platforms.
sentative-color narrowband. We But it is a complex program that can be intimi-
It includes everything
youll need to create
often use dierent telescopes, cameras, software, dating to a beginner.
stunning results ready to and processing techniques to achieve beautiful I found that adopting a standard workow
print, like this photo of results. And although Ive used a variety of equip- helped me to become familiar with this power-
IC 417 above. The author ment over the years, Ive settled on one program ful software and to streamline my own process-
supplied all photos with to work up all of my deep-sky images from start ing routine to get the best results from those
this article. to nish: PixInsight (pixinsight.com). rare clear nights. Heres how I do it.

66 August 2016 sky & telescope

Processing Flow
To begin, there are several ways to access PixInsights
processes and scripts. The easiest is using the pull-
down menu along the top of the screen. You can nd all
processes under Process > All Processes. To its right, the
Script menu contains a standard set of scripts, organized
in groups (Utilities, Image Analysis, Batch Processing,
and more). You can download other scripts, or record your
own to further streamline your own workow.
My typical processing routine involves 5 main steps:
1. Reducing my data to a single master for each lter.
2. Linear processing of the color and luminance (unl-
tered monochrome) stacked separately. This
includes combining the red, green, and blue les
into a color image and enhancing it with Hydrogen-
alpha (H) data, if shot.
3. Nonlinear stretching.
4. Combining the luminance and color data.
5. Final tweaks to the photo to prepare it for publishing
or printing.
QUALITY CONTROL The Blink process lets you quickly inspect
Following this general outline has helped raise the your images and reject any with clouds or poor tracking.
quality of the images I produce and also keeps me
from skipping important processes. With a few minor
modications, this workow can be used for image les shot color images or correcting hot and cold pixels with
generated by any type of camera, including DSLR and the CosmeticCorrection processes (both found in the
one-shot color CCD images. Light tab). Once everything is loaded and ready, I choose
where to save my calibrated les in the Output Directory
Data Reduction section and click the Run button in the bottom right.
A night of CCD imaging can generate dozens of les, When BPP is complete, Ill open all the calibrated
not to mention many calibration frames the bias images taken with all my lters and align them all using
frames, dark frames, and at-eld images used to clean the ImageRegistration > StarAlignment process. Be sure
up the light (target) exposures. Data reduction is the to select the reference image you identied earlier as
process of making single master images from the your alignment target.
many raw les I record of my chosen target. It involves Now its time to combine all my sub-exposures using
selecting the best frames and then calibrating, aligning, the ImageIntegration process (found at Process > Image-
and combining them into a nal (though still unpro- Integration > ImageIntegration), selecting one single-
cessed) result. Because I use a monochrome camera lter group at a time. PixInsight includes four integra-
with color and narrowband lters, I often shoot through tion processes, but ImageIntegration is the workhorse.
3 to 5 lters to produce a color image (red, green, and I choose the best combination method for each lters
blue, and sometimes luminance and H).
The rst tool in my image-processing workow is the
Blink process, which lets me inspect each image and
discard any that appear to be of poor quality (images
with clouds, poor tracking, and so on). PixInsights
SubframeSelector script (Script > Batch Processing >
SubframeSelector) can automatically evaluate images
and sort them into approved or rejected groups using
quality criteria you can modify. When evaluating image
quality, I use this opportunity to identify the best one to
use as a reference when aligning images.
With my best frames in hand, I then apply the Batch-
Preprocessing (BPP) script. BPP is how I gather my cali-
bration frames and generate masters from each group,
and then apply these to my images. This script also DATA REDUCTION Image calibration can be automated in PixInsight using
performs additional functions, such as debayering one- the BatchPreprocessing script.

Sk yandTelescope.com August 2016 67

 Imaging Technique

pixels. If only a few spots need cleaning up, Ill use the
clone stamp tool found at Process > Painting > Clone-
Stamp; if I nd many, Ill apply the CosmeticCorrection
process again. Next, Ill crop out any non-overlapping
edges in my images using the DynamicCrop process.
This tool crops each image exactly the same, to remove
areas that could interfere with later processing steps.
My next action is to address any light-pollution gra-
dients in the images. Gradients can severely limit the
quality of the nal picture, particularly in a color image.
Fortunately, there are two excellent tools in PixInsight
to x these problems: AutomaticBackgroundExtraction
(ABE) and DynamicBackgroundExtraction (DBE). Both
work well on individual les or a color image. (See S&T:
Sep. 2014, p. 68, for a detailed article on using these
powerful functions.)
Now Ill combine my individual red, green, and blue
images into a color result using Process > ChannelMan-
agement > ChannelCombination. This tool should auto-
matically assign your ltered images to their respective
channels, but if not, they can be selected manually. Click
the blue Apply Global circle at the bottom left of the
window and in a moment your color-combined image
will appear. Be sure to save the result.
Often the color image will appear to have a strong
bias toward one color. This can be corrected using the
ColorCalibration process, but in dicult cases, apply-
ing the BackgroundNeutralization process rst can
help. Both often work well without any changes to their
STACKING The ImageIntegration process generates a master default settings.
frame from a group of calibrated and aligned images. Hovering At this point, Ill add any H data to the color image
over a selection (in this case the Rejection algorithm) displays if available. Many experienced imagers struggle with
helpful tips about the options available. blending H into a color image. Fortunately, PixInsight
has an excellent script for the job. The NBRGBCombi-
data set, depending on how many sub-exposures Im nation script (under Script > Utilities) is very easy to
combining. The program will open a description of each use and produces a rich, natural-looking red color in
method when the cursor is hovered over each option for emission nebulae without aecting star colors. With the
a few seconds. Once Ive loaded the tool with the images
to be combined, I apply the process by clicking the blue
circle at the bottom left of the window.
In a few moments, the data reduction is complete,
producing a single stacked result. Ill save this le and
then repeat the process for each lter group.

Linear Image Processing

After data reduction is complete, Ill open up each of
my stacked results. These images will appear very dark,
with only a handful of stars visible. This is because most
deep-sky objects are much fainter than starlight, so they
get recorded at the shadow region of the histogram. We
can stretch the display in PixInsight using the Screen-
TransferFunction process to better display the shadow
regions, which doesnt modify the actual data. SCREEN STRETCH Use the ScreenTransferFunction pro-
Before performing any additional processing, Ill cess to display an image while continuing to work with it in its
inspect the images carefully for any leftover hot and cold unstretched (linear) state.

68 August 2016 sky & telescope

script open, Ill select my color image in the RGB Source
Image section and the H image in the Narrowband
for R channel (eg Ha). Because H also emits at blue
wavelengths, adding some hydrogen-alpha signal to the
blue channel can make for a more natural-looking result,
though reduce the Scale setting in the blue channel to
about 0.02 and click Apply. Its usually necessary to re-
balance the color on the blended image.
With my color data assembled, its time to address the
luminance channel. I often shoot an unltered lumi-
nance image, which has the benet of recording faint
details with a very high signal-to-noise ratio compared
to the color data. This can then be added to the color
picture to produce a very smooth, detailed result. The
strong signal recorded in my luminance data can then
be deconvolved to reduce blurring due to atmospheric
turbulence. Deconvolution is a complex mathemati-
cal process that reverses some of the degradation and
enhances small-scale details in the image. Getting it
right takes a fair amount of experimentation (and will be GRADIENT KILLER Samples are placed on an image of M81
to remove a light-pollution gradient using the DynamicBack-
detailed in an upcoming issue).
groundExtraction process.
Noise Reduction ADDING NARROWBAND PixInsight makes it easy to
My next step is to address noise in the image using the enhance a color image with hydrogen-alpha data using the
MultiscaleLinearTransform (MLT) process. This tool can NBRGBCombination script.

Sk yandTelescope.com August 2016 69

 Imaging Technique

GOING NON-LINEAR Once youve cleaned up and deconvolved the image, it needs to be permanently stretched using the His-
togramTransformation process. Move the middle caret toward the left to bring out the mid-range of the data, and then move the left
caret toward the right to darken the background.

isolate small-, medium-, and large-scale noise kernels, toward the left. This boosts the midtones of the image,
allowing noise reduction to be targeted only in the areas though it also increases the background levels. Ill x this
where its needed. I always apply MLT to both my color by moving the left caret toward the right, which controls
and luminance images, usually with the same settings the black point in the image. To preserve signicant data,
for both. For each Layer from 1 to 4, I adjust the Thresh- I never adjust the white point, as doing that tends to bloat
old and Amount sliders to get the desired result. Try a and overexpose the stars. Similarly, I only move the black
Threshold of 3 and Amount of 0.5 for Layer 1, and lower point enough to darken the background without clipping
values for each subsequent layer up to Layer 4 (noise out any faint details in the image.
reduction cannot be applied to the R, or residual, layer).
The built-in masking feature should be activated to pro- Working with Nonlinear Images
tect stars and other high-signal areas. The default mask With my image stretched after basic cleanup, its time to
settings usually work well. be a little more artistic. This is where I can sharpen the
Now its time to stretch the image and make it nonlin- luminance image, perform additional noise reduction,
ear. There are a few dierent ways to do this in PixInsight, add it to the color data, and adjust the contrast and satura-
but I prefer the HistogramTransformation process. Click- tion. I prefer to work mostly on the Luminance channel
ing the blue circle at the bottom left of the tools window and then blend it into the color image near the end.
activates the Real-Time Preview mode. Before making At this point I want to selectively process regions
any adjustments, I reset the Screen TransferFunction so the image. This is where Masks come in. Masks are
the Real-Time Preview displays an accurate preview of extremely important when processing nonlinear images
the results of stretching. Next, Ill slide the middle caret in PixInsight. These are black-and-white images that I

70 August 2016 sky & telescope

overlay on the picture Im working on, allowing pro- the ColorCalibration menu, can be applied with default
cesses to modify only the parts of the image I choose. settings to match the brightness of two images. Just
The program oers two main ways to make masks: specify the source image and drag the triangle (New
RangeMask is used for selecting a range of brightnesses Instance) icon to the target image.
and can make masks that include stars and extended After my LRGB image is created, I might use the
objects like galaxies. As its name implies, the StarMask CurvesTransformation process to adjust contrast, bright-
process generates masks that isolate the stars. Both of ness, and color saturation. Additional tweaks such as
these tools are intuitive to use, and tool tips are available sharpening are performed using UnsharpMask, and I
to help you set each slider. In some cases, the luminance might also employ ExponentialTransormation to bring
channel of a color image can make an excellent mask. up faint features. The use of masks is advised for all of
Luminance can be extracted from a tricolor image using these steps, with only the nal contrast and saturation
the ChannelExtraction command in Lab mode. A copy tweaks on the unmasked image.
of a greyscale image can also make a good mask. Any
image can be copied by dragging the view identier tab Sharing Online and in Print
at upper left of the image window to an empty spot on Once my image is ready, Ill upload it to my website
the PixInsight workspace. More complex masks can be and, of course, send it to Sky & Telescope. Id strongly
created from simple masks using PixelMath, and there advise serious imagers to invest in a color-managed
are some mask-related scripts, like ColorMask, that are workow so that others see your images the same way
sometimes helpful. Once Ive made a mask, Ill use the you do. Its best to use a hardware monitor calibration
selections in the Mask menu on the main toolbar to device such as the Spyder tools available from datacolor.
select, invert, or remove it. com. With a calibrated monitor and PixInsights color
Although I performed some noise reduction before management and proong tools enabled and properly
stretching, an additional application is often necessary congured, my images look as good in print as they
at this stage. I prefer to use the TGVDenoise process on do online. All the settings and history of your project,
nonlinear les. I tend to apply it only to the darkest areas including masks, processes, workspaces, and more, can
of the luminance image, using a mask to protect stars be saved for reference at a later date (File > Save Project).
and other structures. After applying noise reduction, A nal tip nd some constructive and friendly crit-
the image can be stretched again by moving the black ics on various online imaging forums. Many there know
and mid-point carets again taking care not to clip any what it takes to make a compelling astrophoto, and they
signicant data. might give you just the idea you need to make a great
I can now combine the luminance with the color picture even better.
image using the LRGBCombination process. The best
results are usually obtained when the two images being Ron Brecher images deep-sky objects from his home observa-
combined have a similar brightness. LinearFit, found in tory in Guelph, Ontario. Visit his website at astrodoc.ca.

FINAL CURVES
Far left: The Curves process
allows you to simultane-
ously adjust the brightness
and contrast of the image
(white), and the saturation
(pink), as well as the
individual color channels.

ADDING LUMINANCE
Left: Use the LRGBCombi-
nation process to replace
the brightness of an RGB
image with Luminance data
processed separately. The
contribution of each to the
nal result is controlled
with the Transfer Functions
sliders, and noise reduction
can be applied to the color
image, all in one process.

Sk yandTelescope.com August 2016 71

Book Review
S. N. Johnson-Roehr

Big Science, Small Science

Black Hole Blues and Other Songs from Outer Space

Janna Levin While descriptions of

Alfred A. Knopf the work at and the
256 pages, ISBN 9780307958198, facilities of LIGO are
$26.95, hardcover scattered throughout
the book, most of the
chapters in Black Hole
Black hole blues, Janna Levins new book on Blues are framed around
LIGO (Laser Interferometer Gravitational-Wave Obser- individual voices
vatory) and the search for gravitational waves, builds on those of Weiss, Thorne,
a deep literature analyzing big science big-facility and Drever, but also of
projects that employ large numbers of scientists and physicist Joe Weber and
sta from various institutions, all supported by mas- astronomer Jocelyn Bell
sive budgets. In its current state, LIGO epitomizes big Burnell, as well as LIGO
science: the detection of gravitational waves required administrator Rochus
multiple teams at multiple institutions to develop Robbie Vogt. Levin
multiple instruments at multiple sites over multiple is at her best when she
decades. But as Levin shows, the early work in the eld comes closest to ethnography. The ideas and motivations
of gravitational waves resembled more closely small sci- of the troika and collaborators ring through distinctly,
ence, with research conducted by individuals or small despite her mediating prose. In fact, as I read, I found
teams bound to a single university or institution. In a myself becoming more invested in the lives of the
small science setting, the scientists functioned semi- individual actors than in the project itself. Admittedly, I
autonomously and so were able to respond to data and knew going in that Advanced LIGO (a series of upgrades
ideas with as much or as little exibility as they saw t. moved LIGOs instruments from initial to advanced
In Black Hole Blues, Levin documents LIGOs trans- via an enhanced state) had successfully detected gravi-
formation from small to big, chronicling particularly tational waves on September 14, 2015. I was much less
well the growing pains during its development from a sure about the outcome for the people who started the
few ideas at individual labs to one of the largest projects project, however. As it turns out, I had good cause to be
ever funded by the National Science Foundation. She worried about a few of the books protagonists.
tells LIGOs story through biography and anecdotes, Black Hole Blues should appeal to anyone interested
many of which were related to her during interviews in the workings of big science, whatever the eld
with several of the primary actors from the projects physics, astronomy, molecular biology. The workings
early years. These include Rainier Weiss and Kip of these massive research projects, the balancing of
Thorne, two of the three physicists referred to as LIGOs demands made by the various stakeholders, from scien-
troika (as explained late in the book, out of necessity tists to adminstrators, are not often seen by the public,
Levin relies on an oral history recorded in 1997 for most simply because its hard to get a birds-eye view of such
of her discussion of the third physicist in the troika, Ron large endeavors. While there are better and deeper expla-
Drever). Personality as much as practicality shaped the nations of gravitational waves already written, Levin
founding years of LIGO, and as the search for gravi- gives her readers a satisfying look at how big science
tational waves stretched over years and even decades, starts, develops, and in the end succeeds.
succeeding generations of scientists and administrators
inherited a project formed by the competing approaches Observing Editor S. N. Johnson-Roehr divides her time
of these three physicists. between staring at the sky and staring at the pages of a book.

72 August 2016 sky & telescope

 J. Kelly Beatty
Gallery

CORONA OF MANY COLORS

Wolfgang Strickling
The total solar eclipse on March 9th drew many photog-
raphers to the track of totality in Indonesia. This dramatic
view results from using a handheld polarizing lter ori-
ented 0 with respect to celestial north for the red channel,
60 for green, and 120 for blue. This polarization arises
from scattering of radiation by free electrons.
Details: Canon EOS 850D DSLR camera at ISO 100
with 500-mm mirror lens. Exposures: 0 and second.

SkyandTelescope.com August 2016 73

 Gallery

BREATHTAKING BEADS
Li-Chun Chen
Images taken just as totality began and ended on March 9th capture Bailys beads, the vesti-
gial glints of sunlight that stream through low-lying terrain along the lunar limb. Since the
Moon moves eastward, the sense of motion in this dramatic sequence is from right to left.
Details: Mizar FA-80 apochromatic refractor and Nikon D800 DSLR camera at ISO 100. Expo-
sures: 200 second each for the bead sequences and 00 second for mid-totality.

MAGICAL MOUNT RAINIER

Matthew Dieterich
An auroras pink glow, a sky lled
with trailed stars, snow-capped
Mount Rainier, and Reection
Lake create a picture-perfect
combination good enough to be
chosen for a stamp celebrating the
U.S. National Parks centennial.
Details: Nikon D750 DSLR camera
at ISO 5000 and 24-mm lens. Total
exposure: 27 minutes over 2 hours.

DELICATE DETAILS
Brian Peterson
Sharpless 170, about 6,500 light-
years distant in Cassiopeia, is a
faint cloud of ionized hydrogen
energized by a hot central star.
Details: Hyperion 12.5-inch f/8 astro-
graph and SBIG STL-11000 CCD
camera used with H and RGB
lters. Total exposure: 10 hours.

74 August 2016 sky & telescope

 POL AR PROMINENCE
Han-Chang Weng
Prominences often come into view when the
Moon completely covers the Sun. But this one,
seen during Marchs total eclipse, rose 65,000
km above the Suns north pole and remained
visible throughout totality.
Details: Takahashi FSQ-106ED astrograph
and Nikon D800 DSLR camera at ISO 400.
Exposure: 000 second.

Sk yandTelescope.com August 2016 75

 Gallery

HEART OF THE SUN

Mohammad Talafha
Members of the UAEs Sharjah Center for Astronomy
and Space Sciences took advantage of exceptional see-
ing on April 12, 2016, to record Active Region 2925,
whose heart-shaped umbra was three times Earths size.
Details: Baader 180-mm apochromatic refractor with white-
light solar lter and GigE DFK 33G274 CCD video camera.

COMPLEXIT Y IN CORONA AUSTRALIS

Brett Soames & Ron Brecher
Located just south of Sagittarius, Corona Australis is
often overlooked by observers. But its dusty molecular
cloud is one of the closest star-forming regions. NGC
6541, the globular cluster at right, is 13 billion years old.
Details: Takahashi FSQ-106N astrograph and SBIG STL-
11000M CCD camera with Astrodon Gen2 LRGB lters.
Total exposure: 8 hours.

Gallery showcases the nest astronomical images submitted to us

by our readers. Send your best shots to gallery@SkyandTelescope.com.
See SkyandTelescope.com/aboutsky/guidelines.

76 August 2016 sky & telescope

 ECLIPSE OVER TERNATE
Babak Tafreshi
The small Indonesian island of Ternate proved pop-
ular with eclipse chasers last March. A patchwork
of clouds adds to the drama as the Moons shadow
races across the volcano-dotted landscape.
Details: Nikon D810A DSLR camera at ISO 1600 and
35-mm lens. Exposure: 0 second.

SOL AR CORONAS MAGNETIC THREADS

Mikhail Semenov, Andrey Oleshko, Aleksandr Yuferev
A painstaking 123-image composite reveals exqui-
site coronal details during the total solar eclipse
on March 9, 2016. Note the ghostly features on the
Moon, its landscape lit up by a full Earth.
Details: Sky-Watcher BK 80ED refractor with Canon
EOS 650D camera (ISO 200, 400, 800); Canon EOS
550D camera (ISO 400, 800) with 200-to-400-mm
zoom lens at 200 mm. Exposures: 000 to 1 second.

Visit SkyandTelescope.com/gallery
for more of our readers astrophotos.

Sk yandTelescope.com August 2016 77

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Sk yandTelescope.com August 2016 81

 Inside This Issue
Specialty astronomy equipment dealers and manufacturers are an important resource for amateur and professional
astronomers alike patronize our advertising dealers in this issue and enjoy all the benets of their expertise.

Product Locator
BINOCULARS MOUNTS SOFTWARE
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To advertise on this page, please contact Peter Hardy at 617-758-0243, or Ads@SkyandTelescope.com

82 August 2016 sky & telescope

 Index to Advertisers

Ash Manufacturing Co., Inc.. . . . . . . . . . . 9 Observa-Dome Laboratories. . . . . . . . . . 65

Astro Haven Enterprises . . . . . . . . . . . . . 79 Oceanside Photo & Telescope . . . . . . . . 61 SkyandTelescope.com

800-253-0245
Astronomics . . . . . . . . . . . . . . . . . . . . . . 80 Optic Wave Laboratories. . . . . . . . . . . . . 80
IN THE NEXT ISSUE
Astro-Physics, Inc. . . . . . . . . . . . . . . . . . . 80 Peterson Engineering Corp. . . . . . . . . . . 79

Beatrice/Gage Co Nebraska Tourism . . . . 9 PlaneWave Instruments. . . . . . . . . . . . . . . .9

Bobs Knobs . . . . . . . . . . . . . . . . . . . . . . . .78 PreciseParts . . . . . . . . . . . . . . . . . . . . . . . .78

Durango Skies . . . . . . . . . . . . . . . . . . . . . .79 Shelyak Instruments . . . . . . . . . . . . . . . . 79

Equatorial Platforms . . . . . . . . . . . . . . . . .78 Sky & Telescope . . . . . . . . . . . 9, 15, 57, 61, 65

Explore Scientic - Bresser . . . . . . . . . . . .13 Sky-Watcher USA . . . . . . . . . . . . . . . . . . . . . 3

Strong Prospects
for Weak Lensing
Farpoint Astronomical Research . . . . . . .78 Software Bisque . . . . . . . . . . . . . . . . Cover 3 Astronomers are studying gravitys
minute distortions on galaxy images to
see the invisible dark matter.
Glatter Instruments . . . . . . . . . . . . . . . . . .78 Stellarvue . . . . . . . . . . . . . . . . . . . . . . . . . 80
Astronomy and Big, Big Data
How will astronomers cope with the
International Dark-Sky Association . . . . 80 Summer Star Party . . . . . . . . . . . . . . . . . . . . 9 tsunamis of astrodata expected from the
Large Synoptic Survey Telescope and
other wide-eld surveys?
iOptron . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Technical Innovations . . . . . . . . . . . . . . . . 79
Observing Through
JMI Telescopes . . . . . . . . . . . . . . . . . . . . . . 78 Tele Vue Optics, Inc. . . . . . . . . . . Cover 2, 7 a Truly Large Telescope
Bob Naeye recounts his experience with
Mount Wilsons 100-inch reector, once
Kasai Trading Co., Ltd. . . . . . . . . . . . . . . 79 TelescopeAdapters.com . . . . . . . . . . . . . 78 the worlds largest telescope.

Beyond the Dawes Limit

Knightware . . . . . . . . . . . . . . . . . . . . . . . . . . 80 TravelQuest . . . . . . . . . . . . . . . . . . . . . . . . . 81 Your scope may show tighter double
NASA, ESA, M.J. JEE AND H. FORD (JOHNS HOPKINS UNIVERSITY)

stars than its supposed to. Heres a list

of pairs to try.
Lunatico Astronomia . . . . . . . . . . . . . . . . . 79 University Optics, Inc. . . . . . . . . . . . . . . . . 79

Navigating AutoStakkert! 2
Mathis Instruments . . . . . . . . . . . . . . . . . . 79 Vixen Optics . . . . . . . . . . . . . . . . . . . . . . . 80 Explore this frame-stacking program for
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Meade Instruments Corp. . . . . . . 5, Cover 4 Willmann-Bell, Inc. . . . . . . . . . . . . . . . . . . . 79 On newsstands July 26th!

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SkyandTelescope.com August 2016 83

 Focal Point Rod Mollise

The Go To War
Despite recent stirrings, its over, and happily so the benets of Go To are legion.

I thought the Go To War, the long- M13. There it was looking beautiful in about the objects you observe is far more
running debate about whether real ama- the eyepiece. M5? Yep. M8, M20, M92, important than just knowing how to
teur astronomers use telescopes that point and all the rest of the summer wonders locate them.
automatically at sky objects, was over. But succumbed to the LX200 as quickly as I Once I admitted this realization to
this sometimes-heated controversy seems could push its buttons. myself, I began to see the good the new
to be aring up again in online forums That left only the question of whether telescopes could do for our hobby. Plenty
where amateurs gather and at the clubs I amateur astronomers should use Go To. of people enter astronomy, become
visit. Me? Im all for computerized scopes, Early on, when the subject came up at enthusiastic about it, and then drop out.
since theyre one of the few things attract- club meetings, I sided with the curmud- Once they get past the Moon, bright
ing new blood into our avocation. geons complaining about the coee planets, and a vivid deep-sky object or
I didnt always feel this way. I rst got grinder scopes, with their whirring two, they run out of interesting things
my hands on the technology more than motors, that were springing up like weeds to observe. They havent yet mastered
20 years ago, in late 1992 to be exact. A fel- on our observing elds. You had to be locating objects with a star chart and
low club member invested his entire IRS able to navigate the sky to be an amateur nderscope and get bored. Go To changes
refund in a Meade LX200, the rst aord- astronomer. Familiarity with the stars is all that. With just a little help and instruc-
able Go To Schmidt-Cassegrain, and one central to our avocation. tion, novices can see dozens of celestial
evening he brought it to our clubs dark While I believed, and still believe, treasures from the get-go.
site, where I was cruising along with my learning the sky is benecial for a num- Something else convinced me Go To
6-inch Dobsonian. Ha, I thought, that ber of reasons especially the feeling of is a good thing: the way the blas faces
thingll never work. Get a horse! accomplishment it brings Ive decided of teenagers at our clubs public outreach
How wrong I was. My buddy invited thats not what makes you an amateur sessions lit up at the sight of computerized
me to give the Go To a try. Punched in astronomer. Instead, knowing something telescopes. And they really lit up when one
member sent her scope to targets wire-
lessly with a smartphone. Kids like com-
puters and phones, and if thats a hook to
get them into astronomy where theyll
nd that computers are just the tip of the
iceberg, coolness-wise so be it.
Actually, I dont know why Im wor-
ried whether the Go To debate might be
creating divisions among us again. Its
clear the war is over. Go To is here to stay.
Dont like it? Dont use it. If you enjoy
hunting for objects, by all means hunt.
But stay focused on product, the enjoy-
ment of the sky, rather than process, the
type of tool we use to reach night-sky
nirvana.

Contributing Editor Rod Mollise has two

S&T: LEAH TISCIONE

other articles in this issue: Visual Filters for

Deep-Sky Observing (page 28) and Space-
walking with the Meade MWAs (page 58).

84 August 2016 sky & telescope

ITS
WORTH
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QUALITY
The LX90 comes with Advanced Coma-Free Optics (ACF) and
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EASE
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STABILITY
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VALUE
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