Celestial Sphere
Celestial Sphere
● Our lack of depth
perception when we
look into space creates
the illusion that Earth
is surrounded by a
celestial sphere.
● In reality, stars that
appear very close
together in our sky
may actually lie at
very different
distances from Earth.
Points on the Celestial Sphere
• North and south celestial
poles
• Celestial equator
• REMEMBER: These are
points /lines on the celestial
sphere and NOT on the
Earth
Ecliptic:
– The Sun's apparent annual
path among the
constellations
– Tilted 23.5° from the
equatorial plane
Cardinal Points on the Ecliptic
• Vernal (Spring) Equinox
• Sun crosses the equator
• Length of day = length of night = 12
hours at the equator
• Summer Solstice
• Sun is highest in the sky
• Autumnal (Fall) Equinox
• Sun crosses the equator
• Length of day = length of night = 12
hours
• Winter Solstice
• Sun is lowest in the sky
Other Points on the
Celestial Sphere
• Constellations along the
ecliptic are called “Zodiac”
• The visible ones change
through the year because the
Earth orbits the sun.
• The constellations themselves
are arbitrary groupings of stars
in the sky.
• The stars at night in the
summer are up during the
daytime in winter.
Equatorial coordinate system
(coordinates fixed on the celestial sphere)
• right ascension (RA)
– Similar to longitude; it is the east-west distance between the vernal equinox and
a location on the celestial sphere.
– Measured in units of time: hours, minutes, seconds
» 0 h – 24 h from Vernal Equinox towards east
» Ex. Sirius has RA =
6 h 45 m OR 6:45
Don’t confuse RA with time on your watch!
• declination (Dec)
– Similar to latitude; it is the north-south distance between the celestial equator
and a location on the celestial sphere.
– Measured in degrees:
» 0 ° to 90 ° – north from celestial equator
» 0 ° to -90 ° – south from celestial equator
Equatorial coordinate system
Comparing latitude and longitude
to
declination and right ascension
F
D Practice
B
Which star is found near
A 23 hr, -30°?
E
What are the approximate
coordinates for star A?
C
G
F
D Your turn!
B
Which star is found near
A 2 hr, +40°?
E
What are the approximate
coordinates for star G?
C
G
Latitude and Longitude
Geographic Coordinate System
Latitude
• Lines of Latitude run horizontally
• Latitude is measured in degrees.
• The Equator is 0° Latitude.
• Lines of Latitude locate places North or South of the
Equator.
• The North Pole is 90° N Latitude, and the South Pole is 90° S
Latitude.
The Tropics
23 ½ ° North Latitude
23 ½ ° South Latitude
The Arctic and Antarctic Circles
Summer Solstice (Northern Hemisphere)
Winter Solstice (Northern Hemisphere)
Longitude
• Lines of Longitude run vertically.
• They are also called Meridians.
• The Prime Meridian is found in Greenwich, England.
• The Prime Meridian is 0° Longitude.
• Lines of Longitude locate places East or West of the
Prime Meridian.
• There are 180° of east Longitude, and 180° of west
Longitude.
Time Zones
• Time zones are broad strips that measure 15 degrees wide.
• Time zones differ from
their neighboring time
zones by 1 hour.
• The continental
U.S. has 4 time
zones, Eastern,
Central, Mountain,
and Pacific.
Local Time and Universal Time
Local Time- is what we use everyday, and regulates our
lives. It’s the time where we are.
Examples of Local Time are: meal time, sleep time, work
time, and school time
Universal Time- is what we use when we need a time that
is agreed upon marking time world-wide.
An example when Universal Time was used was when a
supernova in 1987 was first seen. Astronomers, and
Astronauts use Universal Time.
• Greenwich Mean Time- is the time that
is registered at Greenwich, England.
**Greenwich Mean Time is another
name for Universal Time.
The International Dateline was
established following the 180th
meridian, where ever we cross it the
date advances 1 day ( if you are going
west), or goes back 1 day (if you are
going east).
