How to compute the solar zenith angle

I wanted to solve for the solar zenith angle and tried to search online on how to do it. It says that the solar zenith angle is the angle of sun away from vertical. Or it can be computed using the formula:

Solar zenith angle = 90 (degrees) - sun angle (angle above horizon)

One site has this equation:

Sun zenith angle = ( pi / 2 ) - (sun elevation angle, in radians)

Looking closely, the two equations are just the same. Next question is, what is the sun elevation angle?

I was lead to few sites that were very helpful. The sites provide a table of the altitude and azimuth of the Sun or Moon during a specific day, at a time interval that you specify. Cool huh!

Here are the sites I found:

1. The Astronomical Applications Department of the U.S. Naval Observatory

2. Geoscience Australia

3. More information here about Sun Angle, Axial Tilt and Solar Radiation at the Surface, Solar Radiation Flux to the Outside of the Atmosphere, Seasons.