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Where is it?
On the Celestial Sphere
Longitude and Latitude
On Earth:
Longitude is how far you are, in degrees,
East or West of the “Prime Meridian”
which goes from the North Pole through
Greenwich England and on to the South
Latitude is how far you are, in degrees,
north or south of the Equator which is 0°.
The North Pole is 90° North.
Right Ascension (RA)
On the Celestial sphere:
Right Ascension is like Longitude.
The Right Ascension of an object is how far east
an object is from a line that runs from celestial
pole to the other through the vernal equinox.
Unlike longitude Right Ascension is measured in
Hours, Minutes and Seconds.
24 hours is once around.
Declination (Dec)
Declination is how far an object is north or
south of the celestial equator in degrees.
It is just like latitude in everyway.
The Equator is 0° Declination, The celestial
poles are at 90° North and South
The Tropic of Cancer is a declination line
along about 23°27’ North.
The Tropic of Capricorn is
The Location of Celestial Objects
All Celestial objects can be located:
• In the sky at a given time with Altitude and Azimuth
But that changes due to the motion of the celestial
• On the Celestial Sphere with Right Ascension and
The RA and Dec of almost all celestial objects stay the
The Objects in the Solar System
The Motions of the Sun, Moon and
Ancients noticed that the Sun, Moon, Planets
(and the other objects in the solar system)
move across the celestial sphere.
“Planet” means wanderer in Greek.
So…their Right Ascension and Declination are
always changing.
They move on paths that are close to, and
intersect the ecliptic
They also move with the Celestial Sphere