Astronomical Coordinate Systems

A Comparative Summary of Astronomical Coordinate Systems

Coordinate System	Horizon (Sky)	Equatorial		Ecliptic	Galactic
Physical Basis	Direction of Gravity	Earth's Rotation		Earth's Orbital Motion	Galactic Plane
Fundamental Great Circle	Horizon	Celestial Equator		Ecliptic	Galactic Plane
Poles	Zenith, Nadir	North and South Celestial Poles		Ecliptic Poles	Galactic Poles
Secondary Great Circles	Vertical Circles	Hour Circles		Secondaries to Ecliptic	Secondaries to Galactic Equator
Latitude-Like Coordinate	Altitude	Declination		Celestial Latitude	Galactic Latitude
Latitude-Like Coordinate	Altitude	Zero-Point Affixed to Sky	Zero-Point Affixed to Earth	Celestial Latitude	Galactic Latitude
Longitude-Like Coordinate	Azimuth	Right Ascension	Hour Angle	Celestial Longitude	Galactic Longitude
Longitude-L Coord. Zero-Point	North Point of Horizon	Vernal Equinox	Celestial Meridian	Vernal Equnox	Galactic Center
+ Direction of Long.-L Coord.	Eastward	Eastward	Westward	Eastward	Eastward
Used for:	Casual Reference, Some Telescopes, Altitude of an object must be known to determine the atmospheric refraction of its position and its atmospheric extinction.	Cataloging Positions	Setting Telescope	Solar System Structure	Galactic Structure