Ubvri photometry of some lunar topographies

Abstract

Examples of ‘pure’ lunar mountains, dark and light maria, and cratered terrae have been observed with the UBVRI stellar photometry system. Johnson's (1965) absolute calibration was used to compute brightnesses. These brightnesses were reduced using Hapke's photometric model to a standard geometry (angle of incidence 60°, emergence 40°, phase 90°), and relative albedos were then computed. The mountains, as distinct from the other regions, appear to require a wavelength dependent phase function. The albedos for the four topographic types are approximately linear functions of wavelength. The terrae are redder than the maria. Very low contrast between the topographies is predicted for full-moon at wavelengths shorter than 0.30μ. On the basis of laboratory studies, the lunar particles are comparable to basalt grains having sizes less than 50μm. Larger particle sizes are associated with the dark maria and smaller ones with the cratered highlands.