Solar zenith angle

The solar zenith angle is the angle between the sun and the vertical direction at a specific location on the Earth's surface. More technically, it is defined as the angle measured from the point directly overhead (the zenith) to the line extending to the center of the sun. In simpler terms, a solar zenith angle of 0 degrees means the sun is directly overhead, while an angle of 90 degrees means the sun is on the horizon.