A model of the brightness of moonlight

Abstract

A knowledge of the brightness of moonlight is needed for detailed calculations of the limiting magnitude of astronomical detectors, whether they be visual, photographic, or electronic. The previous literature contains no method for making even crude estimates and has few actual measurements of moonlight brightness. In this paper we report new measurements of the sky brightness from the 2800-m level of Mauna Kea. In addition, we present a model for predicting the moonlight as a function of the Moon's phase, the zenith distance ofthe Moon, the zenith distance of the sky position, the angular separation of the Moon and sky position, and the local extinction coefficient. The model equations can be quickly calculated on a pocket calculator. A comparison of our model with our lunar data and with some Russian solar data shows the accuracy of our predictions to range from 8% to 23%.