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 1 to 5 minutes (silver bromide prints) and 25 to 45 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 negative prints, see image C024/9977.
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