A photometric investigation of the lunar crater rays |
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| Authors: | J Van Diggelen |
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| Institution: | (1) The Astronomical Institute, University of Utrecht, Holland |
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| Abstract: | This investigation deals with accurate photometric data concerning a number of rays of Tycho, Copernicus, Kepler, and Aristarchus. They have been derived from plates taken at the Yerkes Observatory in a night of a total lunar eclipse near phase angle 0°. By comparing the normal albedo with that of the surroundings of the rays we found that they can be interpreted as samples of telescopically unresolved bright patches. The fractional areak covered by these patches varies along the ray and shows that they are composed of a number of separate ray elements. The observed value ofk is in accordance with counts on a Ranger photograph.The distribution of the brightness along the rays has also been compared with the mass distribution of the ejecta in the rays around terrestrial explosion craters. The mean length of the lunar rays is in full accordance with its extrapolated terrestrial value. We cannot assume, however, that the rays are regions covered with a homogeneous layer of white powder, because the comparison with the terrestrial explosion craters gives an unprobable value for the height of the layer of the ejecta. The same results follow now from the photometric properties of the rays.From a comparison with the difference in albedo at the Surveyor's footprints follows the suggestion that the lunar rays are composed of bright patches, where the surface material came into a state of lower porosity, while it has a higher porosity in the dark halos around the craters. A suspected dark halo around Tycho has photometrically been measured and the results prove that it really exists. Kepler also shows a very weak halo. |
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