The coordinate system in which a celestial object's position on the celestial sphere is described in terms of its celestial latitude
and celestial longitude
, measured with respect to the ecliptic
. Celestial latitude is measured in degrees north or south of the ecliptic, and celestial longitude is measured in degrees eastward from the vernal equinox
. Because the ecliptic is fixed among the stars (that is, it is unaffected by the precession of the Earth's axis),
an object's celestial latitude does not alter over time. However, due to the gradual precession of the equinoxes westward along the ecliptic, an object's celestial longitude increases by about 1.4° each century. The ecliptic system is used by astronomers especially in describing the position of objects within the solar system.
Compare altazimuth coordinate system