The position of the
Sun in the sky is a function of both time and the
geographic coordinates of the observer on the surface of the
Earth. As the Earth moves around the Sun during the course of the
year, the Sun appears to move with respect to the
fixed stars on the
celestial sphere, along a path called the "
ecliptic". The
Earth's rotation about its axis causes the fixed stars to move in the sky in a way that depends on the observer's geographic
latitude. The time when a given fixed star crosses the observer's
meridian depends on the geographic
longitude. To find the Sun's position for a given observer at a given time, one may therefore proceed in three steps: