Radio observations of the moon have been made over the range of wave lengths from 4.3 mm to 75 cm, and the results are summarized in Table 1. Observations have also been made at 1.5 mm using optical techniques (Sinton, 1955, 1956,; see also chap. 11). Not all the observers have used the same procedures or made the same assumptions about the lunar brightness distribution when reducing the data, and this, together with differences in the methods of calibrating the antennae and receivers, must account for much of the disagreement in the measured radio brightness temperatures.

In the observations at 4.3 mm (Coates, 1959 a), the diameter of the antenna beam, 6'.7, was small enough to allow resolution of some of the larger features of the lunar surface, and contour diagrams have been made of the lunar brightness distribution at three lunar phases. These observations indicate that the lunar maria heat up more rapidly and also cool off more rapidly than do the mountainous regions. Mare Imbrium seems to be an exception and remains cooler than the regions which surround it. These contour diagrams also suggest a rather rapid falloff in the radio brightness with latitude.

Very recently, observations have been made at 8 -- mm wave length with a reflector 22 meters in diameter with a resultant beam width of only about 2' (Amenitskii, Noskova, and Salomonovich, 1960). The constant temperature contours are much smoother than those observed at 4.3 mm by Coates (1959 a), and apparently the emission at 8 mm is not nearly so sensitive to differences in surface features. Such high-resolution observations as these are needed at several wave lengths in order that the radio emission of the moon can be properly interpreted.