The Moon's Temperature at λ=2.77cm

The study of the thermal radio emission of the moon and planets began in 1946 with the detection of the thermal radiation of the moon at 1.25cm wavelength by Dicke and Beringer [1]. This was followed three years later by a comprehensive series of observations of the radiation from the moon at 1.25cm wavelength over three lunar cycles by Piddington and Minnett [2] showing that the thermal radiation from the moon at this short wavelength varied during a lunar cycle in a roughly sinusoidal fashion. The temperature, however, was much smaller than the change in the surface temperature of the moon as known from infrared observations. The maximum of radio radiation was found about 3.5 days after the maximum of the surface temperature at full moon. With the very insensitive instruments of that time it was rather difficult to measure a few Kelvin at a system temperature level of several thousand Kelvin. Now, 55 years later, I repeated such measurements with standard consumer equipment bought from the supermarket. Nowadays one can buy a complete satellite receiving system composed of a parabola mirror, a LNC (low noise converter) and a satellite receiver for the frequency range of 10.7GHz to 12.7GHz for less than 200 Swiss francs. Such a satellite system has a ~100 times lower system temperature than the original one of Dicke and Beringer; thus one can expect a system temperature of less than Tsys=70 Kelvins. With this paper I want to demonstrate that it is possible to repeat classical radio astronomy experiments with really cheap hardware. My own measurements over two complete cycles from 6 January until 8 march 2001 confirm within fairly large error bars the measurements of Dicke, Beringer and a few others [3, 4, 5]. I measured a mean temperature of Tmean=213 Kelvin. The minimum was about Tmin=192 Kelvin ~2,5 days prior to full moon while the maximum with 236 Kelvin was about ~5 days after full moon.