Surface Temperature Variations during the Lunar Nighttime

A new photometer incorporating a mercury-doped germanium photoconductor has been used with a 19-inch telescope to measure the 8-14- brightness temperatures of the shaded lunar surface. Right- ascension scans carried into the lunar nighttime from the terminator show a characteristic of cooling inconsistent with the occurrence of a thick homogeneous dust layer. It appears th more highiy conducting material either is exposed commonly on the surface or constitutes a substratum generally covered by no more than a centimeter or so of the strongly insulating dust. No difference in nighttime temperature distribution was observed between maria and uplands. However, local areas of higher-thanaverage brightness temperature were encountered. These indicate extensive exposures of consolidated material. Local temperature anomalies of this type are associated with the bright-rayed craters Tycho and Copernicus, but they are distributed over an area larger than that represented by the respective craters. Two other groups of temperature anomalies were found in otherwise undistinguished mare border areas. These observations and others suggest that surface redistribution processes are operative on the lunar surface over at least a 10-meter range, but are not important over distances much in excess of a kilometer.