Radiative enhancement of lunar hot spots during eclipse

Equilibrium surface temperatures along the bottoms of lunar craters and near ridges during eclipse are calculated by taking into account radiation from the crater walls. Crater temperatures are enhanced in proportion to the ratio of crater depth to crater diameter. Comparison with ratios derived from Baldwin's empirical relationship between depth and diameter shows that radiative enhancement increases with decreasing crater diameter. The enhancement at the crater center amounts to about 5.5°, 3.5°, and 2°K for diameters of 0.1, 1.0, and 10 km, respectively. The enhancement between the center and the wall is slightly larger. Scatter about Baldwin's empirical relation indicates that ratios of depth to diameter as large as 0.25 occasionally occur, implying a radiative enhancement at the crater center of 9°K and a slightly greater enhancement between the center and the walls. Thermal anomalies reported by Saari and Shorthill also increase with decreasing crater size, but most anomalies exceed the radiative enhancement. The most probable primary cause of the thermal anomalies still appears to be a relatively large thermal conductivity within certain craters. However, radiative enhancement is not negligible for smaller crater diameters.