Multicolor photoelectric photometry of the Lunar surface

Abstract

Results obtained during an extensive photometric and colorimetric study of the lunar surface are presented. The observations were made using a three-beam photoelectric photometer capable of recording the light intensity in three wavelength bands simulataneously. The observations fall into three categories: (1) the brightness versus phase variation for lunar details: (2) the color index versus phase variation; and (3) the color distribution of areas of the Moon. (1) The brightness variation with phase was studied for 23 selected lunar features. From the point at which the terminator crossed the area the brightness was found to rise almost linearly with phase up to phase angles within ±10° of full moon. (2) Various color indices were used in a search for a color variation with phase angle. Color index measurements having one passband in the red above 6000 Å and a second in the blue show a reddening with the phase angle of 0 m dot 0019±0.0005 per degree. Comparisons between two short wavelengths or two more above 6000 Å do not show any evidence of reddening. (3) Color contrasts across the lunar surface were estimated on the basis of measurements of over 200 points. Distinct color differences are found which do not always correspond to visible boundaries on the Moon.