Coordinate Systems
The following table lists the common coordinate systems in use by the astronomical community. The fundamental plane divides the celestial sphere into two equal hemispheres and defines the baseline for the vertical coordinates, analogous to the equator in the geographic coordinate system. The poles are located at ±90° from the fundamental plane. The primary direction is the starting point of the horizontal coordinates. The origin is the zero distance point, the "center of the celestial sphere", although the definition of celestial sphere is ambiguous about the definition of its center point.
| Coordinate system | Center point (Origin) |
Fundamental plane (0º vertical) |
Poles | Coordinates | Primary direction (0º horizontal) |
|
|---|---|---|---|---|---|---|
| Vertical | Horizontal | |||||
| Horizontal (also called Alt/Az or El/Az) |
observer | horizon | zenith / nadir | altitude (a) or elevation | azimuth (A) | north or south point of horizon |
| Equatorial | center of the Earth (geocentric) / center of the Sun (heliocentric) | celestial equator | celestial poles | declination (δ) | right ascension (α) or hour angle (h) | vernal equinox |
| Ecliptic | ecliptic | ecliptic poles | ecliptic latitude (β) | ecliptic longitude (λ) | ||
| Galactic | center of the Sun | galactic plane | galactic poles | galactic latitude (b) | galactic longitude (l) | galactic center |
| Supergalactic | supergalactic plane | supergalactic poles | supergalactic latitude (SGB) | supergalactic longitude (SGL) | intersection of supergalactic plane and galactic plane | |
Read more about this topic: Celestial Coordinate System
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