Editing Astronomical coordinate systems (section)

===Ecliptic system===
{{Main|Ecliptic coordinate system}}
The fundamental plane is the plane of the Earth's orbit, called the ecliptic plane. There are two principal variants of the ecliptic coordinate system: geocentric ecliptic coordinates centered on the Earth and heliocentric ecliptic coordinates centered on the center of mass of the Solar System.

The geocentric ecliptic system was the principal coordinate system for ancient astronomy and is still useful for computing the apparent motions of the Sun, Moon, and planets.<ref>[[Asger Aaboe|Aaboe, Asger]]. 2001 ''Episodes from the Early History of Astronomy.'' New York: Springer-Verlag., pp. 17–19.</ref> It was used to define the twelve [[astrological sign]]s of the [[zodiac]], for instance.

The heliocentric ecliptic system describes the planets' orbital movement around the Sun, and centers on the [[Center of mass#Barycenter in astrophysics and astronomy|barycenter]] of the Solar System (i.e. very close to the center of the Sun). The system is primarily used for computing the positions of planets and other Solar System bodies, as well as defining their [[orbital elements]].