Ecliptic

The ecliptic is the plane defined by the Earth’s orbit around the Sun and represents the apparent annual path of the Sun on the celestial sphere. In geodesy and related space-geodetic techniques, the ecliptic serves as an important reference plane in celestial coordinate systems and in the definition of astronomical parameters. Its orientation is relevant for modeling Earth orientation, precession–nutation, and for the precise transformation between terrestrial and celestial reference frames used in geodetic positioning and Earth rotation studies.