Observations in the wavelength range 1 to 3 mm

Abstract

Measurements at these wavelengths are likely to give more information than those carried out at longer wavelengths since appreciable changes in the brightness temperature are found, not only throughout a lunation, but also during eclipse. The lunation measurements give 0·36 ± 0·05 for the ratio of thermal to electromagnetic attenuation coefficients at 1·5 mm wavelength. During total eclipse a drop of 30% in the mean disk brightness temperature at this wavelength has been measured. The two results taken together are not consistent with models of the lunar surface which suppose a thin dust layer of lower thermal conductivity but otherwise the same physical properties as the under­lying rock. Polarization and isothermal mapping measurements have been made with telescopes capable of resolving areas small compared with the total lunar disk. From these measure­ments an effective dielectric constant of about 2 has been deduced. These results together with measurements made at other wavelengths will be interpreted in terms of a rough model for the lunar surface. At present, in order to get more detailed information, there is a need for a greater wave­length and angular resolution. The use of etalons and large optical telescopes will be indicated.