ROYAL ASTRONOMICAL SOCIETY / SCIENCE PHOTO LIBRARY ROYAL ASTRONOMICAL SOCIETY / SCIENCE PHOTO LIBRARY
Photochart of polar stars. Three types of photographic prints are shown here: silver bromide prints (exposed using gaslight), platinotype prints (exposed using diffused sunlight), and a photozincograph. The exposure times range from 20 to 60 seconds (silver bromide prints) and 3 to 30 minutes (platinotype prints). Two circular (polar projection) engravings are also shown. The observations were carried out by on 14 August 1888 by British amateur astronomer and engineer Isaac Roberts (1829-1904). For transparencies, see image C024/9978.
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