![]() ![]() A reséau (grid) of cross-lines 5 mm apart was to be photographed on each plate to facilitate the determination of positions of stars. Each set was to be taken in duplicate, the centres of one series being at the corners of the other. According to this scheme two sets of photographs, each covering 2º by 2º (on a scale of about 1 mm to 1 minute of arc) were to be taken on 16-cm square photographic plates: one with long exposure (40 minutes) to form a photographic map of the whole sky (Astrographic Chart), and the other with short exposures (6m, 3m, and a supplementary exposure of 20s) from which a catalogue of reference stars was to be formed (the Astrographic Catalogue). There, a scheme was approved for the photographic mapping of the heavens by the concerted action of a number of observatories in both hemispheres with a standardised telescope. On the invitation of the French Academy of Sciences, an International Congress on Astronomical Photography, was held in Paris in April 1887 April. The French brothers Paul and Prosper Henry saw the potential for revolutionising the process of chart making and developed a photographic telescope with an objective of 13 inches aperture. The results were striking and attracted considerable attention, not so much for the image of the comet, but for the clarity of the surrounding field of stars. This was the first time a camera had been so mounted. The Carte du Ceil has its origins in a photograph taken of the Great Comet of 1882 at the Cape Observatory, with a camera strapped onto an equatorial telescope. It is still in dome D at Herstmonceux today. It stayed at Greenwich until 1956/7 when it was moved to Herstmonceux where it was re-erected in dome D in August 1957. Mothballed during the Second World War, the telescope was brought back into use at Greenwich in 1947/8. ![]() From 1905, the object glass began to be used in eclipse expeditions and from 1922, the whole telescope. The Astrographic Refractor contributed to both the Carte du Ciel and the Astrographic Catalogue. Made by Sir Howard Grubb of Dublin, it consisted of a 13-inch photographic refractor with a focal length of about 11 feet 3 inches (3.43m), firmly connected to a parallel 10-inch visual guiding telescope of the same focal length on a German Equatorial mount. Known to have been published in Pearson's Magazine in 1896, this higher quality reproduction is taken from the Greenwich Astrographic Catalogue, Volume 1, (HMSO, 1904)Ordered in 1888 and delivered in 1890, the 13-inch Astrographic Refractor was one of a number of similar telescopes that were commissioned around that time to take part of an international project to produce a photographic map of the sky (Carte du Ciel). Photo by the London Stereoscopic and Photographic Company. ![]()
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