Photometry of Venus: I. Observation of the brightness distribution over the disk |
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| Authors: | A Dollfus H Camichel C Boyer M Auriere E Bowell J Nikander |
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| Institution: | Observatoire de Paris-Meudon and Observatoire du Pic-du-Midi, France |
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| Abstract: | Isophotes of the luminance distribution over the disk of Venus at several phase angles and in several wavelengths are constructed by means of isodensitometry of high-quality photographic negatives of Venus. Twenty-three plates were selected from more than 2000 original negatives available at the IAU Planetary Photographs Center of Meudon Observatory. Six isophote maps were made from a series of yellow light images (λ = 5850Å), corresponding to phase angles from 22° to 129°. Special attention was paid to the rare occurrences of distinct features in yellow light. A sequence of isophote maps was taken in six wavelengths from λ = 5850 to 3250Å. The ultraviolet cloud markings appear as changes in the isophote configurations for different wavelengths. Variations of contrast with wavelengths are deduced. Dark features, almost invisible at 4500Å, reach a contrast of 25% at 3500Å which then no longer increases toward ultraviolet. The polar bright clouds give contrasts of 40% to 60% in ultraviolet. A series of images taken in ultraviolet at 3500Åshows configurations characteristic of observations at short wavelengths for both the waxing and the waning crescent.In Parts II and III of this series of papers, the isophote maps will be compared with theoretical curves computed from the theory of multiple-order scattering by aerosol particles. |
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