A Photovisual Investigation of the Brightness of 59 Areas on the Moon.

This is the authors' abstract. We don't add key points for this paper.

The brightness, on a uniform scale, of 59 areas on the surface of the moon, at eleven phase angles, was determined photovisually from plates taken at the Lowell Observa- tory. It was found that the variation of brightness is similar for all the areas and depends strongly on the angle of reflection as well as on the azimuth between the incident and the reflected rays. On the assumptions that the surface is pitted with spheroidal cups whose contribution to the brightness is proportional to the projected area of the visible illuminated surface, and that the surface between the cups is plane and that its brightness follows Lambert's law, it is possible to represent the observed variation for small angles of reflection. When the angle of reflection is great, the com- puted brightness is a maximum for normal incidence and not at full moon, as observed. There is, however, a large dependence of the brightness on the azimuth