A number of lunar features extending over a range in both morphological type and selenographic coordin- ates have been measured photoelectrically in U, B, and V. The observations extend from 28 in phase angle before full moon to 28 after. They have been measured during several lunations so that a continuous brightness versus phase curve is precluded by the differences in libration. This is a necessary technique for obtaining that component of brightness variation that arises from variations in the local altitude of the earth above the lunar horizon. The nature of the photometric function corresponding to the average be- havior of nearly all the observations has been investigated and found to substantiate the previous conclu- sions, based on an analysis of photographic observations according to an entirely different approach, that the functional dependence on (g, A 0, Ae+) can be well approximated by a dependence on (g,a). A numerical comparison with earlier photographic results has not been made. Deviations from the average photometric function have been correlated with stratigraphic class (hence, probably, age). Correlations of geometrically normalized brightness with stratigraphy, characteristic slope, and color index are presented. A conjectural hypothesis relating these correlations to the evolution of the lunar surface is offered for further study.
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Wildey et al. (1964) studied this question.