The zenith angle is an angle measured from the 
-axis in spherical coordinates,
denoted 
in this work.
It is also known as the polar angle and colatitude.
Zenith Angle
See also
Azimuth, Colatitude, Polar Angle, Spherical CoordinatesExplore with Wolfram|Alpha
References
Zwillinger, D. (Ed.). "Spherical Coordinates in Space." §4.9.3 in CRC Standard Mathematical Tables and Formulae. Boca Raton, FL: CRC Press, pp. 297-298, 1995.Referenced on Wolfram|Alpha
Zenith AngleCite this as:
Weisstein, Eric W. "Zenith Angle." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/ZenithAngle.html