Color differences on the lunar surface

An observational study was made to determine the spectral reflectivity differences (color differences) on the lunar surface in the extended visible wavelength region. A 21-filter (0.4–0.8 μ), double-beam photoelectric photometer was designed, constructed, and used to observe differentially eighty-three areas (some areas being observed many times) to an accuracy of 0.1 to 0.3%. Many color variations were observed up to 10% with some to about 60%. Relative color was dependent on phase angle, but there was no temporally varying luminescence. The broad-band shape on spectral reflectivity curves suggested absorption features and possibly some less broad, low-amplitude (0.2–0.5%) humps. Spectral curve shape appeared dependent on lunar morphology, but there was no universal dependence of color on brightness. These results are interpreted as indicating that color differences are caused mainly be compositional differences and that the shape of spectral reflectivity curves may give some indication of the rock and mineral composition of the lunar surface.