Lunar photometry: a photoelectric study of a lunar eclipse and a measurement of the earth's albedo

The purpose of the project reported here was threefold. First it was to design and construct a dry ice cooled photoelectric photometer suitable for astronomical intensity and color measurements. Second, it was to use that photometer to make intensity and color measurements of selected areas of the lunar surface during the progress of a lunar eclipse. Such observations, it was thought, would produce a partial mapping of the earth's shadow at the lunar distance and might possibly display other effects such as, perhaps, thermal lirniinescen.se of the lunar surface. Third, a measurement of the earth's albedo (reflectivity) was sought, in blue and visual light, according to the standard "UBV" color system. This measurement was to be made by using the photometer to observe the earthshine, or ashen light, on the moon. That is, the (reflected) light from the earth, which is, in turn, reflected back to earth by the moon. These objectives were, in the main, achieved. Construction of the photometer was begun in January, of 1968. The first telescope observations to be reported here were made on 18 October 1968. Although several later attempts were made, they were all clouded out. The telescope used was a 12 inch f6.5 Newtonian reflector located in the Kingsburg Observatory at Kingsburg, California, some twenty miles south of Fresno.