Altitude and Azimuth
The position of the sun at any instant with respect
to an observer on the ground is defined by its altitude angle and its azimuth angle. The altitude of the sun is the angle between the horizon and the sun’s position above the horizon. The altitude varies during the day, beginning and ending at 0º at sunrise and sunset and reaching a daily maximum at solar noon. The altitude angle at noon varies from day to day, reaching a yearly maximum on June 21 (the summer solstice), a minimum on December 21 (the winter solstice), and a point halfway between the two on the vernal and autumnal equinoxes (March 21 and September 21). The azimuth (also called the solar bearing angle) is the angle along the horizon between the projected position of the sun and true (solar) south. Note that the azimuth is referenced from south herein, whereas in other sources it is sometimes referenced from north; there is no clear consensus on this issue. Refer to Fig. 6.3 and Tables C.11 to C.18 for solar position and insolation information.
Referring to the graphic relationships in Fig. 6.2, the height of the sun in the sky (altitude angle) depends upon the observer’s position on the Earth (the latitude) and the seasonal changes (the tilt of the Earth).