Microwave Thermal Radiation from the Moon

Abstract

Measurements have been made of the thermal radiation from the moon in a 15 Mc/s. band, centred at 24,000 Mc/s. The radiation from the whole lunar disk has been measured during several phase cycles. Temperatures corresponding to this radiation have been deduced and curves of temperature against phase angle drawn. One of these corresponds to average temperature over the disk and the other to the temperature of a point on the lunar equator. They are found to be approximately sinusoidal, with amplitude ± 40.3 °K, and ± 52.0 °K. respectively and with a phase lag behind the lunar phase angle of about 45° in each case. These results conflict with previous measurements of temperature at long infra-red wavelengths in both amplitude and phase angle of the temperature curve. An explanation is given in terms of radiation from subsurface layers of the moon's crust, which are partially transparent to the electromagnetic waves with which we are dealing. The theory is developed quantitatively and it is found that the results are consistent with the existence of a thin layer of dust covering a solid lunar surface. Estimates are made of the temperatures of the disk of the new moon (156 °K.) and of the deep interior (241 °K.).