Definition:Astronomical Coordinate System
Definition
An astronomical coordinate system is a coordinate system used for locating the position of bodies in the celestial sphere.
In such systems, there is no indication of the distance of such bodies from Earth.
Ecliptic Coordinate System
The ecliptic coordinate system is an astronomical coordinate system in which measurements are based on the ecliptic.
Hence a point on the celestial sphere is located by means of $2$ angular measurements:
- the celestial longitude $\lambda$ is the angular distance measured eastwards along the ecliptic from the vernal equinox
- the celestial latitude $\beta$ is the angular distance measured north or south of the ecliptic.
Equatorial Coordinate System
The equatorial coordinate system is an astronomical coordinate system in which measurements are based on the celestial equator.
Hence a point on the celestial sphere is located by means of $2$ angular measurements:
- the right ascension $\alpha$, which is the angular distance measured eastwards along the celestial equator from the vernal equinox
- the declination $\delta$, which is the angular distance measured north or south of the terrestrial equator.
Galactic Coordinate System
The galactic coordinate system is an astronomical coordinate system in which measurements are based on the galactic equator.
Hence a point on the celestial sphere is located by means of $2$ angular measurements:
- the galactic longitude $l$, which is the angular distance measured eastwards along the galactic equator from the galactic center
- the galactic latitude $b$, which is the angular distance measured north or south of the galactic equator.
Horizontal Coordinate System
The horizontal coordinate system is an astronomical coordinate system in which measurements are based on the celestial horizon.
Hence a point on the celestial sphere is located by means of $2$ angular measurements:
- the azimuth $A$, which is the angular distance measured eastwards along the celestial horizon from the north point
- the altitude $h$, which is the angular distance measured north or south of the celestial horizon.
Also see
- Results about astronomical coordinate systems can be found here.
Sources
- 1998: David Nelson: The Penguin Dictionary of Mathematics (2nd ed.) ... (previous) ... (next): astronomical coordinate system
- 2008: David Nelson: The Penguin Dictionary of Mathematics (4th ed.) ... (previous) ... (next): astronomical coordinate system