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Halley's Comet
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For other uses, see Halley's Comet (disambiguation).

Halley's Comet, Comet Halley, or sometimes simply Halley, officially designated 1P/Halley, is a
short-period comet visible from Earth every 75–79 years.[1] Halley is the only known short-period
comet that is regularly visible to the naked eye from Earth, and thus the only naked-eye comet that
can appear twice in a human lifetime.[15] It last appeared in the inner parts of the Solar System in
1986 and will next appear in mid-2061.

Halley's periodic returns to the inner Solar System

1P/Halley (Halley's Comet)
have been observed and recorded by
astronomers around the world since at least 240
BC, but it was not until 1705 that the English
astronomer Edmond Halley understood that these
appearances were re-appearances of the same
comet. As a result of this discovery, the comet is
named after Halley.[16]

During its 1986 visit to the inner Solar System,

Halley's Comet became the first comet to be Halley's Comet on 8 March 1986

observed in detail by spacecraft, providing the Discovery

first observational data on the structure of a
Discovered by Prehistoric
comet nucleus and the mechanism of coma and
(observation)
tail formation.[17][18] These observations
Edmond Halley
supported a number of longstanding hypotheses (recognition of
about comet construction, particularly Fred periodicity)
Whipple's "dirty snowball" model, which correctly
Discovery date 1758 (first predicted
predicted that Halley would be composed of a perihelion)
mixture of volatile ices—such as water, carbon
Orbital characteristics[1]
dioxide, and ammonia—and dust. The missions
also provided data that substantially reformed and Epoch 4 August 2061 (2474040.5)
reconfigured these ideas; for instance, it is now
Aphelion 35.14 au[2]
understood that the surface of Halley is largely
(aphelion: 9
composed of dusty, non-volatile materials, and December 2023)[2][3]
that only a small portion of it is icy.
Perihelion 0.59278 au[4]
(last perihelion: 9
Contents
February 1986)
(next perihelion: 28
July 2061)[4]
Pronunciation
Semi-major axis 17.737 au
The common pronunciations of Comet Halley and
Eccentricity 0.96658
Edmond Halley's surname have become largely
unconnected over the years. Comet Halley is Orbital period 74.7 yr
(sidereal)
75y 5m 19d
usually pronounced /ˈhæli/, rhyming with valley, or
(perihelion to
sometimes /ˈheɪli/, rhyming with daily.[19][20] As to
perihelion)
the surname Halley, Colin Ronan, one of Edmond
Halley's biographers, preferred /ˈhɔːli/, rhyming Mean anomaly 0.07323°

with crawly.[21] Spellings of Halley's name during Inclination 161.96°

his lifetime included Hailey, Haley, Hayley, Halley,
Longitude of 59.396°
Hawley, and Hawly, so its contemporary ascending node
pronunciation is uncertain, but the version
Time of perihelion 28 July 2061[4][5]
rhyming with valley seems to be preferred by
≈27 March 2134[6][5]
current bearers of the surname.[22]
Argument of 112.05°
perihelion
Computation of orbit
Earth MOID 0.075 au
(11.2 million km)
Halley was the first comet to be recognized as
(epoch 1968)[7]
periodic. Until the Renaissance, the philosophical
consensus on the nature of comets, promoted by TJupiter -0.598

Aristotle, was that they were disturbances in Physical characteristics

Earth's atmosphere. This idea was disproven in
Dimensions 15 km × 8 km[8]
1577 by Tycho Brahe, who used parallax
measurements to show that comets must lie Mean diameter 11 km[7]
beyond the Moon. Many were still unconvinced
Mass 2.2 × 1014 kg[9]
that comets orbited the Sun, and assumed
instead that they must follow straight paths Mean density 0.6 g/cm3 (average)
[10]
through the Solar System.[23]
0.2–1.5 g/cm3 (est.)
[11]
In 1687, Sir Isaac Newton published his
Philosophiæ Naturalis Principia Mathematica, in Escape velocity ~0.002 km/s
which he outlined his laws of gravity and motion.
Synodic rotation 2.2 d (52.8 h) (?)[12]
His work on comets was decidedly incomplete. period
Although he had suspected that two comets that
Albedo 0.04[13]
had appeared in succession in 1680 and 1681
were the same comet before and after passing Apparent magnitude 28.2 (in 2003)[14]
behind the Sun (he was later found to be correct;
see Newton's Comet),[24] he was unable to
completely reconcile comets into his model.

Ultimately, it was Newton's friend, editor and publisher, Edmond

Halley, who, in his 1705 Synopsis of the Astronomy of Comets,
used Newton's new laws to calculate the gravitational effects of
Jupiter and Saturn on cometary orbits.[25] Having compiled a list
of 24 comet observations, he calculated that the orbital elements
of a second comet that had appeared in 1682 were nearly the
same as those of two comets that had appeared in 1531
(observed by Petrus Apianus) and 1607 (observed by Johannes The orbital path of Halley, against
the orbits of the planets (animation)
Kepler).[25][26] Halley thus concluded that all three comets were,
in fact, the same object returning about every 76 years, a period that has since been found to vary
between 74 and 79 years. After a rough estimate of the perturbations the comet would sustain from
the gravitational attraction of the planets, he predicted its return for 1758.[27] While he had
personally observed the comet around perihelion in September 1682,[28] Halley died in 1742 before
he could observe its predicted return.[29]

Halley's prediction of the comet's return proved to be correct, although it was not seen until 25
December 1758, by Johann Georg Palitzsch, a German farmer and amateur astronomer. It did not
pass through its perihelion until 13 March 1759, the attraction of Jupiter and Saturn having caused
a retardation of 618 days.[30] This effect was computed before its return (with a one-month error to
13 April)[31] by a team of three French mathematicians, Alexis Clairaut, Joseph Lalande, and Nicole-
Reine Lepaute.[32] The confirmation of the comet's return was the first time anything other than
planets had been shown to orbit the Sun. It was also one of the earliest successful tests of
Newtonian physics, and a clear demonstration of its explanatory power.[33] The comet was first
named in Halley's honour by French astronomer Nicolas-Louis de Lacaille in 1759.[33]

Some scholars have proposed that first-century Mesopotamian astronomers already had
recognized Halley's Comet as periodic.[34] This theory notes a passage in the Babylonian Talmud,
tractate Horayot[35] that refers to "a star which appears once in seventy years that makes the
captains of the ships err."[36] Others doubt this idea based on historical considerations about the
exact timing of this alleged observation, and suggest it refers to other astronomical phenomena.[37]

Researchers in 1981 attempting to calculate the past orbits of Halley by numerical integration
starting from accurate observations in the seventeenth and eighteenth centuries could not produce
accurate results further back than 837 owing to a close approach to Earth in that year. It was
necessary to use ancient Chinese comet observations to constrain their calculations.[38]

Orbit and origin

Halley's orbital period has varied between 74 and 79 years since 240 BC.[33][39] Its orbit around the
Sun is highly elliptical, with an orbital eccentricity of 0.967 (with 0 being a circle and 1 being a
parabolic trajectory). The perihelion, the point in the comet's orbit when it is nearest the Sun, is
0.59 au (88 million km). This is between the orbits of Mercury and Venus. Its aphelion, or farthest
distance from the Sun, is 35 au (5.2 billion km) (roughly the distance of Pluto). Unusual for an
object in the Solar System, Halley's orbit is retrograde; it orbits the Sun in the opposite direction to
the planets, or, clockwise from above the Sun's north pole. The orbit is inclined by 18° to the
ecliptic, with much of it lying south of the ecliptic. (Because it is retrograde, the true inclination is
162°.)[40] Owing to the retrograde orbit, it has one of the highest velocities relative to the Earth of
any object in the Solar System. The 1910 passage was at a relative velocity of 70.56 km/s
(157,800 mph).[7] Because its orbit comes close to Earth's in two places, Halley is associated with
two meteor showers: the Eta Aquariids in early May, and the Orionids in late October.[41] Halley is
the parent body to the Orionids, while observations conducted around the time of Halley's
appearance in 1986 suggested that the comet could additionally perturb the Eta Aquariids,
although it might not be the parent of that shower.[42]

Halley is classified as a periodic or short-period comet; one with

an orbit lasting 200 years or less.[43] This contrasts it with long-
period comets, whose orbits last for thousands of years. Periodic
comets have an average inclination to the ecliptic of only ten
degrees, and an orbital period of just 6.5 years, so Halley's orbit is
atypical.[33] Most short-period comets (those with orbital periods
shorter than 20 years and inclinations of 20–30 degrees or less) Orionid meteor originating from
are called Jupiter-family comets. Those resembling Halley, with Halley's Comet streaking the sky
below the Milky Way and to the
orbital periods of between 20 and 200 years and inclinations right of Venus
extending from zero to more than 90 degrees, are called Halley-
type comets.[43][44] As of 2015, only 75 Halley-type comets have been observed, compared with
511 identified Jupiter-family comets.[45]

The orbits of the Halley-type comets suggest that they were originally long-period comets whose
orbits were perturbed by the gravity of the giant planets and directed into the inner Solar System.
[43] If Halley was once a long-period comet, it is likely to have originated in the Oort cloud,[44] a
sphere of cometary bodies around 20,000–50,000 au from the Sun. Conversely the Jupiter-family
comets are generally believed to originate in the Kuiper belt,[44] a flat disc of icy debris between 30
au (Neptune's orbit) and 50 au from the Sun (in the scattered disc). Another point of origin for the
Halley-type comets was proposed in 2008, when a trans-Neptunian object with a retrograde orbit
similar to Halley's was discovered, 2008 KV42, whose orbit takes it from just outside that of Uranus
to twice the distance of Pluto. It may be a member of a new population of small Solar System
bodies that serves as the source of Halley-type comets.[46]

Halley has probably been in its current orbit for 16,000–200,000 years, although it is not possible
to numerically integrate its orbit for more than a few tens of apparitions, and close approaches
before 837 AD can only be verified from recorded observations.[47] The non-gravitational effects
can be crucial;[47] as Halley approaches the Sun, it expels jets of sublimating gas from its surface,
which knock it very slightly off its orbital path. These orbital changes cause delays in its perihelion
of four days on average.[48]

In 1989, Boris Chirikov and Vitold Vecheslavov performed an analysis of 46 apparitions of Halley's
Comet taken from historical records and computer simulations. These studies showed that its
dynamics were chaotic and unpredictable on long timescales.[49] Halley's projected lifetime could
be as long as 10 million years. These studies also showed that many physical properties of Halley's
Comet dynamics can be approximately described by a simple symplectic map, known as the Kepler
map.[50] More recent work suggests that Halley will evaporate, or split in two, within the next few
tens of thousands of years, or will be ejected from the Solar System within a few hundred thousand
years.[51][44] Observations by D. W. Hughes suggest that Halley's nucleus has been reduced in
mass by 80 to 90% over the last 2,000 to 3,000 revolutions.[18]

Structure and composition

The Giotto and Vega missions gave planetary scientists their first
view of Halley's surface and structure. Like all comets, as Halley
nears the Sun, its volatile compounds (those with low boiling
points, such as water, carbon monoxide, carbon dioxide and other
ices) begin to sublimate from the surface of its nucleus.[52] This
causes the comet to develop a coma, or atmosphere, up to
100,000 kilometres (62,000 mi) across.[8] Evaporation of this dirty
ice releases dust particles, which travel with the gas away from
the nucleus. Gas molecules in the coma absorb solar light and
then re-radiate it at different wavelengths, a phenomenon known The nucleus of Halley's Comet,
imaged by the Giotto probe on
as fluorescence, whereas dust particles scatter the solar light.
14 March 1986. The dark coloration
Both processes are responsible for making the coma visible.[15] of the nucleus can be observed, as
As a fraction of the gas molecules in the coma are ionized by the well as the jets of dust and gas
erupting from its surface.
solar ultraviolet radiation,[15] pressure from the solar wind, a
stream of charged particles emitted by the Sun, pulls the coma's ions out into a long tail, which
may extend more than 100 million kilometres into space.[52][53] Changes in the flow of the solar
wind can cause disconnection events, in which the tail completely breaks off from the nucleus.[17]

Despite the vast size of its coma, Halley's nucleus is relatively small: barely 15 kilometres (9.3 mi)
long, 8 kilometres (5.0 mi) wide and perhaps 8 kilometres (5.0 mi) thick.[b] Its shape vaguely
resembles that of a peanut shell.[8] Its mass is relatively low (roughly 2.2 × 1014 kg)[9] and its
average density is about 0.6 grams per cubic centimetre (0.35 oz/cu in), indicating that it is made
of a large number of small pieces, held together very loosely, forming a structure known as a rubble
pile.[10] Ground-based observations of coma brightness suggested that Halley's rotation period
was about 7.4 days. Images taken by the various spacecraft, along with observations of the jets and
shell, suggested a period of 52 hours.[18] Given the irregular shape of the nucleus, Halley's rotation
is likely to be complex.[52] Although only 25% of Halley's surface was imaged in detail during the
flyby missions, the images revealed an extremely varied topography, with hills, mountains, ridges,
depressions, and at least one crater.[18]

Halley is the most active of all the periodic comets, with others, such as Comet Encke and Comet
Holmes, being one or two orders of magnitude less active.[18] Its day side (the side facing the Sun)
is far more active than the night side. Spacecraft observations showed that the gases ejected from
the nucleus were 80% water vapour, 17% carbon monoxide and 3–4% carbon dioxide,[54] with
traces of hydrocarbons[55] although more-recent sources give a value of 10% for carbon monoxide
and also include traces of methane and ammonia.[56] The dust particles were found to be primarily
a mixture of carbon–hydrogen–oxygen–nitrogen (CHON) compounds common in the outer Solar
System, and silicates, such as are found in terrestrial rocks.[52] The dust particles decreased in size
down to the limits of detection (≈0.001 µm).[17] The ratio of deuterium to hydrogen in the water
released by Halley was initially thought to be similar to that found in Earth's ocean water,
suggesting that Halley-type comets may have delivered water to Earth in the distant past.
Subsequent observations showed Halley's deuterium ratio to be far higher than that found in
Earth's oceans, making such comets unlikely sources for Earth's water.[52]

Giotto provided the first evidence in support of Fred Whipple's "dirty snowball" hypothesis for
comet construction; Whipple postulated that comets are icy objects warmed by the Sun as they
approach the inner Solar System, causing ices on their surfaces to sublimate (change directly from
a solid to a gas), and jets of volatile material to burst outward, creating the coma. Giotto showed
that this model was broadly correct,[52] though with modifications. Halley's albedo, for instance, is
about 4%, meaning that it reflects only 4% of the sunlight hitting it; about what one would expect
for coal.[57] Thus, despite appearing brilliant white to observers on Earth, Halley's Comet is in fact
pitch black. The surface temperature of evaporating "dirty ice" ranges from 170 K (−103 °C) at
higher albedo to 220 K (−53 °C) at low albedo; Vega 1 found Halley's surface temperature to be in
the range 300–400 K (27–127 °C). This suggested that only 10% of Halley's surface was active,
and that large portions of it were coated in a layer of dark dust that retained heat.[17] Together,
these observations suggested that Halley was in fact predominantly composed of non-volatile
materials, and thus more closely resembled a "snowy dirtball" than a "dirty snowball".[18][58]

History

Before 1066

Halley may have been recorded as early as 467 BC, but this is
uncertain. A comet was recorded in ancient Greece between 468
and 466 BC; its timing, location, duration, and associated meteor
shower all suggest it was Halley.[59] According to Pliny the Elder,
that same year a meteorite fell in the town of Aegospotami, in
Thrace. He described it as brown in colour and the size of a
wagon load.[60] Chinese chroniclers also mention a comet in that
year.[61]

The first certain appearance of

Halley's Comet in the historical
record is a description from
240 BC, in the Chinese chronicle
Records of the Grand Historian
or Shiji, which describes a Observation of Halley's Comet,
Report of Halley's Comet by comet that appeared in the east recorded in cuneiform on a clay
Chinese astronomers in 240 BC tablet between 22 and 28
and moved north.[62] The only
(Shiji) September 164 BC, Babylon, Iraq.
surviving record of the 164 BC British Museum
apparition is found on two fragmentary Babylonian tablets, now in (BM 41462 Archived 19 April
2021 at the Wayback Machine)
the British Museum.[62]

The apparition of 87 BC was recorded in Babylonian tablets which state that the comet was seen
"day beyond day" for a month.[63] This appearance may be recalled in the representation of
Tigranes the Great, an Armenian king who is depicted on coins with a crown that features,
according to Vahe Gurzadyan and R. Vardanyan, "a star with a curved tail [that] may represent the
passage of Halley's Comet in 87 BC." Gurzadyan and Vardanyan argue that "Tigranes could have
seen Halley's Comet when it passed closest to the Sun on August 6 in 87 BC" as the comet would
have been a "most recordable event"; for ancient Armenians it could have heralded the New Era of
the brilliant King of Kings.[64]

The apparition of 12 BC was recorded in the Book of Han by Chinese astronomers of the Han
Dynasty who tracked it from August through October.[65] It passed within 0.16 au of Earth.[66]
According to the Roman historian Cassius Dio, a comet appeared suspended over Rome for several
days portending the death of Marcus Vipsanius Agrippa in that year.[67] Halley's appearance in
12 BC, only a few years distant from the conventionally assigned date of the birth of Jesus Christ,
has led some theologians and astronomers to suggest that it might explain the biblical story of the
Star of Bethlehem. There are other explanations for the phenomenon, such as planetary
conjunctions, and there are also records of other comets that appeared closer to the date of Jesus'
birth.[68]

If, as has been suggested, the reference by Yehoshua ben

Hananiah in b. Horayot 10a to "a star which arises once in seventy
years and misleads the sailors"[69] refers to Halley's Comet, it
may be a reference to the 66 AD appearance, because this
apparition was the only one to occur during Yehoshua ben
Hananiah's lifetime.[70]
Possible report of Halley's Comet in
the Talmud (b. Horayot 10a)
The 141 AD apparition was recorded in Chinese chronicles.[71] It
was also recorded in the Tamil work Purananuru, in connection with the death of the south Indian
Chera king Yanaikatchai Mantaran Cheral Irumporai.[72]

The 374 AD and 607 approaches each came within 0.09 au of Earth.[66] The 451 AD apparition was
said to herald the defeat of Attila the Hun at the Battle of Chalons.[73]

The 684 AD apparition was recorded in Europe in one of the sources used by the compiler of the
1493 Nuremberg Chronicles, which contains an image 8 centuries after the event.[74] Chinese
records also report it as the "broom star".[75][26]

The 760 AD apparition was recorded in the Zuqnin Chronicle's entry for iyyōr 1071 SE (May 760
AD), calling it a "white sign":[76]

The year [SE] one thousand seventy one (AD 759/760).

In the month of iyyōr (May) a white sign was seen in the sky, before early twilight, in the
north-east [quarter], in the Zodiac [sign] which is called Aries, to the north from these three
stars in it, which are very shining. And it resembled in its shape a broom [...]

And the sign itself remained for fifteen nights, until dawn of the feast of Pentecost.

— Zuqnin Chronicle, fol.136v; Neuhäuser et al. (trans.)

In 837 AD, Halley's Comet may have passed as close as 0.03 au (3.2 million miles; 5.1 million
kilometres) from Earth, by far its closest approach.[77][66] Its tail may have stretched 60 degrees
across the sky. It was recorded by astronomers in China, Japan, Germany, the Byzantine Empire,
and the Middle East;[65] Emperor Louis the Pious observed this appearance and devoted himself to
prayer and penance, fearing that "by this token a change in the realm and the death of a prince are
made known."[78]

In 912 AD, Halley is recorded in the Annals of Ulster, which state "A dark and rainy year. A comet
appeared."[79]

The Zuqnin Chronicle's mention of Halley's The Annals of Ulster's entry for the year 912. It
Comet in 760 AD, alongside an illustration that ends with "Cometis apparuit", i.e. "A comet
includes the relative positions of Aries, Mars and appeared".
Saturn in the sky.

1066

In 1066, the comet was seen in England and thought to be an

omen: later that year Harold II of England died at the Battle of
Hastings and William the Conqueror claimed the throne. The
comet is represented on the Bayeux Tapestry and described in
the tituli as a star. Surviving accounts from the period describe it
as appearing to be four times the size of Venus, and shining with
Halley's Comet in 1066 depicted in
a light equal to a quarter of that of the Moon. Halley came within
the Bayeux Tapestry
0.10 au of Earth at that time.[66]

This appearance of the comet is also noted in the Anglo-Saxon

Chronicle. Eilmer of Malmesbury may have seen Halley in 989 and
1066, as recorded by William of Malmesbury:

Not long after, a comet, portending (they say) a change Halley's Comet seen from London
in governments, appeared, trailing its long flaming hair on 6 May 1066 as simulated by
Stellarium. The Moon, Mars, Jupiter,
through the empty sky: concerning which there was a
and Saturn are also visible.
fine saying of a monk of our monastery called
Æthelmær. Crouching in terror at the sight of the gleaming star, "You've come,
have you?", he said. "You've come, you source of tears to many mothers. It is long
since I saw you; but as I see you now you are much more terrible, for I see you
brandishing the downfall of my country."[80]

The Irish Annals of the Four Masters recorded the comet as "A star [that] appeared on the seventh
of the Calends of May, on Tuesday after Little Easter, than whose light the brilliance or light of The
Moon was not greater; and it was visible to all in this manner till the end of four nights afterwards."
[79] Chaco Native Americans in New Mexico may have recorded the 1066 apparition in their
petroglyphs.[81]

The Italo-Byzantine chronicle of Lupus the Protospatharios mentions that a "comet-star" appeared
in the sky in the year 1067 (the chronicle is erroneous, as the event occurred in 1066, and by
Robert he means William).

The Emperor Constantine Ducas died in the month of May, and his son Michael
received the Empire. And in this year there appeared a comet star, and the
Norman count Robert [sic] fought a battle with Harold, King of the English, and
Robert was victorious and became king over the people of the English.[82]

1145–1378

The 1145 apparition was recorded by the monk

Eadwine. The 1986 apparition exhibited a fan tail
similar to Eadwine's drawing.[75]

Some claim that Genghis Khan was inspired to

turn his conquests toward Europe by the 1222 Illustration on the Eadwine Psalter (fol.10r), from circa
apparition.[83] 1150, portraying a comet that's possibly Halley's
Comet – and describing it as "the long-haired star"
The 1301 apparition may have been seen by the
artist Giotto di Bondone, who represented the Star of Bethlehem
as a fire-colored comet in the Nativity section of his Arena Chapel
cycle, completed in 1305.[75]

Its 1378 appearance is recorded in the Annales Mediolanenses[84]

as well as in East Asian sources.[85]

1456

In 1456, the year of Halley's next apparition, the Ottoman Empire The Adoration of the Magi (circa
1305) by Giotto, who purportedly
invaded the Kingdom of Hungary, culminating in the siege of modelled the star of Bethlehem on
Belgrade in July of that year. In a papal bull, Pope Callixtus III Halley, which had been sighted 4
years before that painting.
ordered special prayers be said for the city's protection. In 1470,
the humanist scholar Bartolomeo Platina wrote in his Lives of the Popes that,[86]

A hairy and fiery star having then made its appearance for several days, the
mathematicians declared that there would follow grievous pestilence, dearth and
some great calamity. Calixtus, to avert the wrath of God, ordered supplications
that if evils were impending for the human race He would turn all upon the Turks,
the enemies of the Christian name. He likewise ordered, to move God by continual
entreaty, that notice should be given by the bells to call the faithful at midday to
aid by their prayers those engaged in battle with the Turk.

Platina's account is not mentioned in official records.

In the 18th century, a Frenchman further embellished
the story, in anger at the Church, by claiming that the
Pope had "excommunicated" the comet, though this
story was most likely his own invention.[87] 1456 comet in Zodiac

Halley's apparition of 1456 was also witnessed in Kashmir and depicted in great detail by Śrīvara, a
Sanskrit poet and biographer to the Sultans of Kashmir. He read the apparition as a cometary
portent of doom foreshadowing the imminent fall of Sultan Zayn al-Abidin (AD 1418/1420–1470).
[88]

After witnessing a bright light in the sky which most historians have identified as Halley's Comet,
Zara Yaqob, Emperor of Ethiopia from 1434 to 1468, founded the city of Debre Berhan (tr. City of
Light) and made it his capital for the remainder of his reign.[89]

1531

Petrus Apianus and Girolamo Fracastoro described comet's visit

in 1531, with the former even including graphics in his publication.

In the Sikh scriptures of the Guru Granth Sahib, the founder of the
faith Guru Nanak makes reference to "a long star that has risen"
at Ang 1110, and it is believed by some Sikh scholars to be a
reference to Halley's appearance in 1531.[90]

1531–1759
Illustration of the 1531 appearance
Halley's periodic returns have been subject to scientific on Petrus Apianus' Astronomicum
Caesareum, noting that a comet's
investigation since the 16th century. The three apparitions from
tail always points away from the sun
1531 to 1682 were noted by Edmond
Halley, enabling him to predict it would
return.[91] One key breakthrough occurred
when Halley talked with Newton about his
ideas of the laws of motion. Newton also
helped Halley get Flamsteed's data on the "I must entreat you to procure for me of Mr Flamsteed what he
has observed of the Comett of 1682 particularly in the month of
1682 apparition.[92] By studying data on September, for I am more and more confirmed that we have
the 1531, 1607, and 1682 comets, he came seen that Comett now three times, since yͤ Yeare 1531, he will
to the conclusion these were the same not deny it you, though I know he will me." —Excerpt of Halley's
letter to Newton about comet's orbits (28 September 1695)
comet, and presented his findings in 1696.
[92]

One difficulty was accounting for variations in the comet's orbital period, which was over a year
longer between 1531 and 1607 than it was between 1607 and 1682.[93] Newton had theorized that
such delays were caused by the gravity of other comets, but Halley found that Jupiter and Saturn
would cause the appropriate delays.[93] In the decades that followed, more refined mathematics
would be worked on, notable by Paris Observatory; the work on Halley also provided a boost to
Newton and Kepler's rules for celestial motions.[92] (See also #Computation of orbit)

Illustrations of prior comet appearances in

the January 1910 Popular Science Monthly magazine
1682 1759 1835

1835

At Markree Observatory in Ireland, an E. J. Cooper used a

Cauchoix of Paris lens telescope with an aperture of 340
millimetres (13.3 in) to sketch Halley's comet in 1835.[94]

The comet was also sketched by F.W. Bessel.[95] Streams of

vapour observed during the comet's 1835 apparition prompted
astronomer Friedrich Wilhelm Bessel to propose that the jet
forces of evaporating material could be great enough to An 1835 watercolour painting
significantly alter a comet's orbit.[96] depicting observation of the 1835
apparition

An interview in 1910, of someone who was a teenager at the time

of the 1835 apparition had this to say:[97]

When the comet was first seen, it appeared in the western sky, its head toward the north and
tail towards the south, about horizontal and considerably above the horizon and quite a
distance south of the Sun. It could be plainly seen directly after sunset every day, and was
visible for a long time, perhaps a month ...

They go on to describe the comet's tail as being more broad and not as long as the comet of 1843
they had also witnessed.[97]

Famous astronomers across the world made observations starting August 1835, including Struve at
Dorpat observatory, and Sir John Herschel, who made of observations from the Cape of Good
Hope.[98] In the United States telescopic observations were made from Yale College.[98] The new
observations helped confirm early appearances of this comet including its 1456 and 1378
apparitions.[98]

At Yale College in Connecticut, the comet was first reported on 31 August 1835 by astronomers D.
Olmstead and E. Loomis.[99] In Canada reports were made from Newfoundland and also Quebec.
[99] Reports came in from all over by later 1835, and often reported in newspapers of this time in
Canada.[99]

Several accounts of the 1835 apparition were made by observers who survived until the 1910
return, where increased interest in the comet led to their being interviewed.[99]

Astrophotography was not known to have been attempted until 1839, as photography was still
being invented in the 1830s, too late to photograph the apparition of 1P/Halley in 1835.[100]

The time to Halley's return in 1910 would be only 74.42 years, one of the shortest known periods of
its return, which is calculated to be as long as 79 years owing to the effects of the planets.[101]

At Paris Observatory Halley's Comet 1835 apparition was observed with a Lerebours telescope of
24.4 cm (9.6 in) aperture by the astronomer François Arago.[102] Arago recorded polimetric
observations of Halley, and suggested that the tail might be sunlight reflecting off a sparsely
distributed material; he had earlier made similar observations of Comet Tralles of 1819.[103]

1910

The 1910 approach, which came into naked-eye view

around 10 April[66] and came to perihelion on 20 April,
[66] was notable for several reasons: it was the first
approach of which photographs exist, and the first for
which spectroscopic data were obtained.[17]
Furthermore, the comet made a relatively close
approach of 0.15 au,[66] making it a spectacular sight.
Indeed, on 19 May, Earth actually passed through the
tail of the comet.[104][105] One of the substances
discovered in the tail by spectroscopic analysis was
the toxic gas cyanogen,[106] which led press to
misquote [citation needed] the astronomer Camille
Flammarion by stating he claimed that, when Earth
passed through the tail, the gas "would impregnate the Halley in April 1910, from Harvard's Southern
Hemisphere Station, taken with an 8-inch Bache
atmosphere and possibly snuff out all life on the
Doublet
planet."[107] Despite reassurances from scientists that
the gas would not inflict harm on Earth,[107] the damage had already been done with members of
the public panic buying gas masks and quack "anti-comet pills" and "anti-comet umbrellas".[108]

The comet added to the unrest in China on the eve of the Xinhai Revolution that would end the last
dynasty in 1911. As James Hutson, a missionary in Sichuan Province at the time, recorded:

"The people believe that it indicates calamity such as war, fire, pestilence, and a
change of dynasty. In some places on certain days the doors were unopened for
half a day, no water was carried and many did not even drink water as it was
rumoured that pestilential vapour was being poured down upon the earth from
the comet."[109]

The 1910 visitation is also recorded as being the travelling companion of Hedley Churchward, the
first known English Muslim to make the Haj pilgrimage to Mecca. However, his explanation of its
scientific predictability did not meet with favour in the Holy City.[110]

The comet was used in an advertising campaign of Le Bon Marché, a well-known department store
in Paris.[111]

The comet was also fertile ground for hoaxes. One that reached major newspapers claimed that the
Sacred Followers, a supposed Oklahoma religious group, attempted to sacrifice a virgin to ward off
the impending disaster, but were stopped by the police.[112]

American satirist and writer Mark Twain was born on 30 November 1835, exactly two weeks after
the comet's perihelion. In his autobiography, published in 1909, he said,

I came in with Halley's comet in 1835. It is coming again next year, and I expect to
go out with it. It will be the greatest disappointment of my life if I don't go out
with Halley's comet. The Almighty has said, no doubt: "Now here are these two
unaccountable freaks; they came in together, they must go out together."[113][114]

Twain died on 21 April 1910, the day following the comet's subsequent perihelion.[115] The 1985
fantasy film The Adventures of Mark Twain was inspired by the quotation.

Halley's 1910 apparition is distinct from the Great Daylight Comet of 1910, which surpassed Halley
in brilliance and was visible in broad daylight for a short period, approximately four months before
Halley made its appearance.[116][117]
 A photograph of Halley's Comet Infographic from the January 1910
taken during its 1910 approach issue of Popular Science Monthly
magazine, showing how Halley's
tail points away from the Sun as it
passes through the inner Solar
System

1986

The 1986 apparition of Halley's Comet was the least favourable

on record. In February 1986, the comet and the Earth were on
opposite sides of the Sun, creating the worst possible viewing
circumstances for Earth observers during the previous 2,000
years.[118] Halley's closest approach was 0.42 au.[119] Additionally,
increased light pollution from urbanization caused many people to
fail in attempts to see the comet. With the help of binoculars, Halley's Comet as seen on 21 March
observation from areas outside cities was more successful.[120] 1986

Further, the comet appeared brightest when it was almost

invisible from the northern hemisphere in March and April 1986,
[121] with best opportunities occurring when the comet could be
sighted close to the horizon at dawn and dusk, if not obscured by
clouds.

The approach of the comet was first detected by astronomers

David C. Jewitt and G. Edward Danielson on 16 October 1982
Kuiper Airborne Observatory's
using the 5.1 m Hale telescope at Mount Palomar and a CCD imaging of Halley's Comet in April
camera.[122] 1986

The first visual observance of the comet on its 1986 return was by
an amateur astronomer, Stephen James O'Meara, on 24 January
1985. O'Meara used a home-built 610-millimetre (24 in) telescope
on top of Mauna Kea to detect the magnitude 19.6 comet.[123] The
first to observe Halley's Comet with the naked eye during its 1986
apparition were Stephen Edberg (then serving as the coordinator
for amateur observations at the NASA Jet Propulsion Laboratory) Animation of 1P/Halley orbit - 1986
and Charles Morris on 8 November 1985.[124][125] apparition
1P/Halley · Earth · Sun
Although the comet's retrograde orbit and high inclination made it
difficult to send a space probe to it,[126] the 1986 apparition gave scientists the opportunity to
study the comet closely and several probes were launched to do so. The Soviet Vega 1 probe
began returning images of Halley on 4 March 1986, captured the first-ever image of its nucleus,[18]
and made its flyby on 6 March. It was followed by the Vega 2 probe, making its flyby on 9 March.
On 14 March, the Giotto space probe, launched by the European Space Agency, made the closest
pass of the comet's nucleus.[18] There also were two Japanese probes, Suisei and Sakigake.
Unofficially, the numerous probes became known as the Halley Armada.[127]

Based on data retrieved by the largest ultraviolet space telescope of the time, Astron, during its
Halley's Comet observations in December 1985, a group of Soviet scientists developed a model of
the comet's coma.[128] The comet also was observed from space by the International Cometary
Explorer (ICE). Originally the International Sun-Earth Explorer 3, the spacecraft departed the Sun-
Earth L1 Lagrangian point in order to intercept comets 21P/Giacobini-Zinner and Halley.[129] ICE
flew about 40.2 million km (25 million mi) from Halley's Comet on 28 March 1986.[130][131]

Two U.S. Space Shuttle missions—STS-51-L and STS-61-E—had been scheduled to observe
Halley's Comet from low Earth orbit. The STS-51-L mission carried the Shuttle-Pointed Tool for
Astronomy (SPARTAN-203) satellite, also called the Halley's Comet Experiment Deployable
(HCED).[132] The mission ended in disaster when the Space Shuttle Challenger exploded in flight,
killing all seven astronauts onboard.[133] Scheduled for March 1986, STS-61-E was a Columbia
mission carrying the ASTRO-1 platform to study the comet,[134] but the mission was canceled
following the Challenger disaster and ASTRO-1 would not fly until late 1990 on STS-35.[135]

1986 USSR miniature sheet, Daily motion across sky during the
featuring Edmond Halley, Comet 1986 passage of Halley's Comet
Halley, Vega 1, Vega 2, Giotto,
Suisei (Planet-A)

After 1986

On 12 February 1991, at a distance of 14.4 au (2.15 × 109 km) from

the Sun, Halley displayed an outburst that lasted for several
months, releasing a cloud of dust 300,000 km (190,000 mi)
across.[52] The outburst likely started in December 1990, and
then the comet brightened from magnitude 24.3 to magnitude
Halley's Comet observed in 2003 at 18.9.[136] Halley was most recently observed in 2003 by three of
28 au from the Sun the Very Large Telescopes at Paranal, Chile, when Halley's
magnitude was 28.2. The telescopes observed Halley, at the
faintest and farthest any comet has ever been imaged, in order to verify a method for finding very
faint trans-Neptunian objects.[14] Astronomers are now able to observe the comet at any point in its
orbit.[14]

On 9 December 2023, Halley's Comet reached the farthest and slowest point in its orbit from the
Sun when it was traveling at 0.91 km/s (2,000 mph) with respect to the Sun.[2][3]

2061

The next perihelion of Halley's Comet is 28 July 2061,[4][5] when

it will be better positioned for observation than during the 1985–
1986 apparition, as it will be on the same side of the Sun as Earth.
[39] The closest approach to Earth will be one day after perihelion.
[7] It is expected to have an apparent magnitude of −0.3,
compared with only +2.1 for the 1986 apparition.[137] On 9
September 2060, Halley will pass within 0.98 au
Animation of 1P/Halley orbit - 2061
(147,000,000 km) of Jupiter, and then on 20 August 2061 will apparition
pass within 0.0543 au (8,120,000 km) of Venus.[7] Sun · Venus · Earth ·
Jupiter · 1P/Halley

2134

Halley will come to perihelion on 27 March 2134.[6][5] Then on 7 May 2134, Halley will pass within
0.092 au (13,800,000 km) of Earth.[7] Its apparent magnitude is expected to be −2.0.[137]

Apparitions

Halley's calculations enabled the comet's earlier appearances to be found in the historical record.
The following table sets out the astronomical designations for every apparition of Halley's Comet
from 240 BC, the earliest documented widespread sighting.[7][138] For example, "1P/1982 U1,
1986 III, 1982i" indicates that for the perihelion in 1986, Halley was the first period comet known
(designated 1P) and this apparition was the first seen in half-month U (the second half of October)
[139] in 1982 (giving 1P/1982 U1); it was the third comet past perihelion in 1986 (1986 III); and it was
the ninth comet spotted in 1982 (provisional designation 1982i). The perihelion dates of each
apparition are shown.[140] The perihelion dates farther from the present are approximate, mainly
because of uncertainties in the modelling of non-gravitational effects. Perihelion dates of 1531 and
earlier are in the Julian calendar, while perihelion dates 1607 and after are in the Gregorian
calendar.[141]

Designation Year Gap Date of Visible Earth Description[142]

BC/AD (years) perihelion[1] duration approach[66]

First confirmed
1P/−239 K1, −239 240 BC – 25 May 15–25 May
sighting.

Seen by
1P/−163 U1, −163 164 BC 76 12 Nov
Babylonians.

Seen by the
6–19
1P/−86 Q1, −86 87 BC 77 6 August Babylonians and
August
Chinese.

August – Watched by
1P/−11 Q1, −11 12 BC 75 10 October 10 0.16 au Chinese for two
October months.

May be the
comet
described in
Josephus's The
Jewish War as
"A comet of the
kind called
Xiphias,
because their
25–26
1P/66 B1, 66 66 78 25 January tails appear to
January
represent the
blade of a
sword" that
supposedly
heralded the
destruction of
the Second
Temple in 70
AD.[67]

Described by
the Chinese as
bluish-white in
colour.
Described in
Tamil literature
22–25 and death of
1P/141 F1, 141 141 75 22 March
March Chera
(Yanaikatchai
Mantaran Cheral
Irumporai) king
after
appearance of
comet.[143]

Described by
the Roman
6 April – historian Dion
1P/218 H1, 218 218 77 17 May
17 May Cassius as "a
very fearful
star".

Seen in China,
1P/295 J1, 295 295 77 20 April 7–20 April but not
spectacular.

Comet passed
13–16 13.5 million
1P/374 E1, 374 374 79 16 February 0.09 au
February kilometres from
Earth.

Appeared
before the
defeat of Attila
the Hun at the
28 June –
1P/451 L1, 451 451 77 28 June Battle of
3 July
Chalons. The
451AD orbital
period was
79.29 years.[1]

27
Noted in China
27 September
1P/530 Q1, 530 530 79 and Europe, but
September – 15
not spectacular.
November

Comet passed
15–26 13.5 million
1P/607 H1, 607 607 77 15 March 0.09 au
March kilometres from
Earth.

First known
Japanese
records of the
comet. Seen in
Europe and
depicted 800
years later in the
2 October
Nuremberg
1P/684 R1, 684 684 77 2 October – 26
Chronicle.
November
Attempts have
been made to
connect an
ancient Maya
depiction of God
L to the event.
[144]

Seen in China,
20 May – at the same time
1P/760 K1, 760 760 76 20 May
10 June as another
comet.

Closest-ever
approach to the
Earth (5 million
km). Tail
25–28
1P/837 F1, 837 837 77 28 February 0.033 au[77] stretched
February
halfway across
the sky.
Appeared as
bright as Venus.

Seen briefly in
1P/912 J1, 912 912 75 18 July 18–27 July China and
Japan.

Seen in China,
5 2–5 Japan, and
1P/989 N1, 989 989 77
September September (possibly)
Korea.

Seen for over

two months in
China. Recorded
in England and
January – depicted on the
1P/1066 G1, 1066 1066 77 20 March 0.10 au
25 March later Bayeux
tapestry which
portrayed the
events of that
year.

Depicted on the
Eadwine Psalter,
with the remark
1P/1145 G1, 1145 1145 79 18 April 15–19 April that such "hairy
stars" appeared
rarely, "and then
as a portent".

Described by
Japanese
astronomers as
being "as large
28 10–28
1P/1222 R1, 1222 1222 77 as the half Moon
September September
. . . Its colour
was white but
its rays were
red".

Seen by Giotto
di Bondone and
included in his
painting The
Adoration of the
22–31 Magi. Chinese
1P/1301 R1, 1301 1301 79 25 October
October astronomers
compared its
brilliance to that
of the first-
magnitude star
Procyon.

Passed within 10
degrees of the
north celestial
pole, more
northerly than at
any time during
the past 2000
10 9–14
1P/1378 S1, 1378 1378 77 years. This is
November November
the last
appearance of
the comet for
which eastern
records are
better than
Western ones.

Observed in
Italy by Paolo
Toscanelli, who
said its head
was "as large as
the eye of an
ox", with a tail
8 January "fan-shaped like
1P/1456 K1, 1456 1456 78 9 June
– 9 June that of a
peacock". Arabs
said the tail
resembled a
Turkish scimitar.
Turkish forces
attacked
Belgrade.

Seen by Peter
Apian, who
noted that its
tail always
1P/1531 P1, 1531 1531 75 26 August 26 August pointed away
from the Sun.
This sighting
was included in
Halley's table.

Seen by
Johannes
27 Kepler. This
1P/1607 S1, 1607 1607 76 27 October
October sighting was
included in
Halley's table.

Seen by
15 15
1P/1682 Q1, 1682 1682 75 Edmond Halley
September September
at Islington.

Return
predicted by
13 March – Halley. First
1P/1758 Y1, 1759 I 1758 76 13 March 25 seen by Johann
December Palitzsch on
1758 December
25.

First seen at the

Observatory of
the Roman
August – College in
16
1P/1835 P1, 1835 III 1835 77 16 August.[145]
November
November Studied by John
Herschel at the
Cape of Good
Hope.

Photographed
for the first time.
20 April – Earth passed
1P/1909 R1, 1910 II, 1909c 1910 75 20 April 0.151 au[7]
20 May through the
comet's tail on
20 May.

Reached
perihelion on 9
February,
closest to Earth
(63 million km)
on 10 April.
1P/1982 U1, 1986 III, 1982i 1986 76 9 February 9 February 0.417 au Nucleus
photographed
by the European
space probe
Giotto and the
Soviet probes
Vega 1 and 2.

Next return with

perihelion on 28
July 2061[4][5]
28 July
2061 75 28 July 0.477 au and Earth
2061[4][5]
approach one
day later on 29
July 2061[7]

Subsequent
return with
27 March perihelion on 27
2134 73 27 March 0.092 au[7]
2134[6][5] March 2134 and
Earth approach
on 7 May 2134

Best-fit for
February 2209
3 February perihelion
2209 75 3 February 0.515 au[146]
2209[146] passage and
April Earth
approach

See also

Halley's Comet in fiction

Kepler orbit

List of Halley-type comets

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Bibliography

Gore, Rick (December 1986). "Halley's Comet '86". National Geographic. Vol. 170, no. 6. pp. 758–785.
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Lancaster-Brown, Peter (1985). Halley & His Comet . Blandford Press. ISBN 0-7137-1447-6.

Needham, Joseph (1959). "Comets, meteors, and meteorites" . Science and Civilisation in China:
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pp. 430–433. ISBN 978-0-521-05801-8.

Sagan, Carl; Druyan, Ann (1985). Comet . Random House. ISBN 0-394-54908-2.

External links

Synopsis of the Astronomy of Comets (1706 reprint of Halley's Wikimedia Commons has
1705 paper) media related to Comet
Halley.
Halley's nucleus by Giotto spacecraft (ESA link)

Image of Halley in 1986 by Giotto spacecraft (NASA link)

cometography.com

1P/Halley at CometBase database

seds.org

Orbital simulation from JPL (Java) / Ephemeris

Donald Keith Yeomans, "Great Comets in History"

A brief history of Halley's Comet (Ian Ridpath)

Photographs of 1910 approach taken from the Lick Observatory from the Lick Observatory Records
Digital Archive, UC Santa Cruz Library's Digital Collections Archived 20 May 2019 at the Wayback
Machine

Numbered comets

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1P/Halley
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