Definition:Equatorial Coordinate System
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Definition
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.
Also defined as
The equatorial coordinate system can also be defined such that a point on the celestial sphere is located by means of:
- the hour angle $t$, which is the angular distance measured westwards along the celestial equator from the vernal equinox, instead of the right ascension
- the north polar distance, which is the complement $90 \degrees - \delta$ of the declination $\delta$.
Also see
- Results about the equatorial coordinate system can be found here.
Historical Note
The equatorial coordinate system is the most widely used of the astronomical coordinate systems.
Sources
- 1998: David Nelson: The Penguin Dictionary of Mathematics (2nd ed.) ... (previous) ... (next): equatorial coordinate system
- 2008: David Nelson: The Penguin Dictionary of Mathematics (4th ed.) ... (previous) ... (next): equatorial coordinate system