Position of the Sun

The position of the Sun in the sky is a function of both the time and the geographic location of observation on Earth's surface. As Earth orbits the Sun over the course of a year, the Sun appears to move with respect to the fixed stars on the celestial sphere, along a circular path called the ecliptic.

Earth's rotation about its axis causes diurnal motion, so that the Sun appears to move across the sky in a Sun path that depends on the observer's geographic latitude. The time when the Sun transits the observer's meridian depends on the geographic longitude.

To find the Sun's position for a given location at a given time, one may therefore proceed in three steps as follows:^[1][2]

1. calculate the Sun's position in the ecliptic coordinate system,
2. convert to the equatorial coordinate system, and
3. convert to the horizontal coordinate system, for the observer's local time and location. This is the coordinate system normally used to calculate the position of the Sun in terms of solar zenith angle and solar azimuth angle, and the two parameters can be used to depict the Sun path.^[3]

This calculation is useful in astronomy, navigation, surveying, meteorology, climatology, solar energy, and sundial design.