Celestial coordinate system
The celestial coordinate system is a virtual horizontal line and a vertical line used to describe the position of an object placed on the celestial sphere. The celestial coordinate system uses a spherical coordinate system to indicate the position of a celestial object in astronomy. In the spherical coordinate system, there must be two reference circles. The reference circle which is the most basic reference is the first reference circle, and the member including the target object is the reference circle. It is divided into an equatorial coordinate system, a horizon coordinate system, an ecliptic coordinate system, and a galactic coordinate system according to the first reference circle.