Lunar Thermal Radiation at 35 KMC

Abstract

Measurements of the thermal radiation of the moon were made at a frequency near 35 kmc to investigate further the variation of the radio-wavelength brightness temperature with lunar phase first observed by Piddington and Minnett at 24 kmc. The subject measurements, when referred to the equivalent blackbody temperature for the center of the lunar disc, show a complex rather than sinusoidal variation with phase, varying between 225° and 145°K. The directivity of the antenna (about 0.2° of arc between halfpower points) was sufficient to indicate the lunar equatorial (eastwest) brightness distribution; this was found to vary in the expected manner and was in agreement with the form of the central brightness variation during a lunation. Observations of two total lunar eclipses showed that no measurable change in lunar radiation occurs during the few hours of an eclipse. Comparison of these results with calculations by Jaeger suggests the lunar surface is composed of a layer of fine dust of very low thermal conductivity, the average depth of which is estimated as one inch or more.