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:

• calculate the Sun's position in the ecliptic coordinate system,
• convert to the equatorial coordinate system, and
• convert to the horizontal coordinate system, for the observer's local time and position.