Planetary Observations
E.C. Slipher was a pioneer in planetary photography. He contributed to advances in astrophotography with innovative techniques to produce high-quality images.
He was one of the first people to use multiple image printing, in which several images taken in close succession are superimposed onto one photographic plate to improve the quality of information content in any given picture. From 1918, Slipher was one of the first to standardize his photographic plates for photometric measures, a practice now generally used.
Slipher also pioneered color filter photography to highlight the features of the planets. For instance, he discovered that elements of the surface of Mars, which one would normally not be able to see if they are photographed in purple, sometimes emerge clearly in yellow light. He called this phenomenon "blue compensation."
He made some of the best images of Venus, Mars, Jupiter, and Saturn of his time. Most of these are featured in his two books, The Photographic Story of Mars (1962), and A Photographic Study of the Brighter Planets (1964). Each set of images illustrates a characteristic detail of the different planets, for example white spots on Saturn, disturbances on Jupiter, atmospheric effects on Venus, and seasonal changes, clouds and melting of the polar cap on Mars.
Slipher’s special interest was the study of Mars. He made visual observations, drawings, and photographs of Mars during favorable oppositions during his three expeditions to South Africa in 1939, 1954, and 1956.
Throughout these trips, he gathered some of the best images of Mars that anyone had taken up to that point. In particular, he captured the first color images of the Red Planet. Although his primary goal was to photograph the controversial Martian canals, his observations added enormously to the understanding of seasonal effects like polar caps, clouds, and dust storms.
