Polarimetric and photometric properties of the Moon: Telescopic observations and laboratory simulations: 1. The negative polarization

Abstract

In 1985–1990 a wide program of photometric and polarimetric observations of the Moon was carried out by means of a new spectropolarimeter which made possible an accuracy of polarimetric measurements up to 0.04%. In order to interpret these and other observations, laboratory photometric and polarimetric measurements of some natural and artificial samples have been made. In the first part of this paper results of linear and parabolic regression analysis for parameters of the negative polarization and photometric characteristics of the Moon are presented. A principal component analysis was also carried out. Only two statistically significant principal components were found: the first is predominantly determined by albedo and the second is controlled by some parameters of the negative polarization. Some relationships between polarimetric and photometric parameters are studied in detail. In particular, a two-branch dependence of polarization degree in the minimum P min vs. albedo A was discovered for both telescope and laboratory measurements. A correlation between P min and the slopes of brightness phase curves at small phase angles was found. It points out a common origin of the negative polarization and the opposition effect. Correlations were found between some color ratios of polarimetric parameters and the color index (0.65 μm/0.42 μm). For instance, on a log-log scale there is a linear dependence of the color ratio of the slopes of polarization phase curves at the inversion angles upon the color index. This contradicts the asteroid polarimetric Q-effect ( B. Zellner and J. Gradie, 1976, Astron. J. 81, 262–280 ).