MICROWAVE OBSERVATIONS AND MODELING OF A LUNAR ECLIPSE

Microwave observations of the Moon during the eclipse of November 28-2 9, 1993, are reported. Observations were made at 1.327 mm wavelength w ith a 12-m-aperture radio telescope. Points observed were at the lunar equator and 42 degrees north and south lunar latitude, all near the s ub-Earth meridian of lunar longitude. Brightness temperature (T-B) was observed to decrease a maximum of 25% below the pre-eclipse value of T-B. Comparisons are made between our observations and previous data s ets collected under similar circumstances. A thermal model has been co nstructed with which we calculate eclipse cooling curves that agree wi th our observations. From this model inferences are made about the por osity of the lunar regolith necessary to produce the observed changes in brightness temperature throughout the eclipse. The effect of rocks resting on top of the regolith on theoretical eclipse cooling curves i s examined. The data are well fit with a regolith-only model that assu mes a density of 1.4 g cm(-3) (porosity of 59%) for the top 1 cm of re golith. Comparison of lunar high latitude with equatorial observations suggests that regolith density increases with depth within this top 1 cm. Inclusion of rocks in the model increases the amplitude of the ec lipse cooling curve for a fixed regolith density, so that a regolith rocks model fitting the data must have a lower regolith density than a regolith-only model. The regolith model described here to explain ob served eclipse cooling curves is shown to be consistent with observed diurnal cooling curves reported by Low and Davidson (1965, Astrophys. J. 142, 1278-1282). (C) 1995 Academic Press, Inc.