Estimating Solar Zenith Angle and Local Time From a Partial Rainbow

               A method of calculating the solar zenith angle and the local time from the photograph of a full rainbow is found in the literature. This paper describes a method of doing the same from the photograph of a partial rainbow as long as one end of the rainbow meets the horizon. The only measurement needed is the angle between the rainbow end and the horizon from the photograph. The solar zenith angle can be calculated from this angle and the half angle of the rainbow cone. Next, the hour angle of the Sun is calculated given the latitude of the location and the declination of the Sun, whence the local time of the occasion is determined.