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These telescopes were termed normal astrographs with an aperture of around 13 inches (33 cm) and a focal length of 11 feet (3.4 m) designed to create images with a uniform scale on the photographic plate of approximately 60 arcsecs/mm while covering a 2° × 2° field of view. Around half of the observatories ordered telescopes from the Henry brothers (Paul and Prosper) in France, with others coming from the factory of Howard Grubb of Dublin. The Astrographic Catalogue Ĭatalogue photographique du Ciel I–VIII published by Helsinki University Observatory in 1937.įor the Astrographic Catalogue, 20 observatories from around the world participated in exposing and measuring more than 22,000 glass plates (see table). Other aspects are covered in various papers in the Proceedings of IAU Symposium Number 133 held in 1988. Most of the Carte du Ciel plates used three exposures of 20 minutes duration, displaced to form an equilateral triangle with sides of 10 arcsec, making it easy to distinguish stars from plate flaws, and asteroids from stars.Ī fascinating contemporary account of this vast international astronomical collaboration, published in 1912, is given by Herbert Hall Turner, then Savilian Professor of Astronomy at Oxford University. These plates were to be reproduced and distributed as a set of charts, the Carte du Ciel, in contrast to previous sky charts which had been constructed from the celestial coordinates of stars observed by transit instruments.
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They yielded a catalogue of positions and magnitudes down to about 11.5 mag, and the programme was largely completed during the first quarter of the 20th century.įor the second goal, a second set of plates, with longer exposures but minimal overlap, was to photograph all stars to 14 mag. The Astrographic Catalogue plates, of typically 6 minutes exposure, were in due course photographed, measured, and published in their entirety. Different observatories around the world were charged with surveying specific declination zones (see table). As a result of the Astrographic Congress of more than 50 astronomers held in Paris in April 1887, 20 observatories from around the world agreed to participate in the project, and two goals were established:įor the first, the Astrographic Catalogue, the entire sky was to be photographed to 11 mag to provide a reference catalogue of star positions that would fill the magnitude gap between those previously observed by transit and meridian circle instrument observations down to 8 mag – this would provide the positions of a reasonably dense network of star positions which could in turn be used as a reference system for the fainter survey component (the Carte du Ciel). Origins and goals Participating observatories and stars measured in the context of the Astrographic Catalogue ObservatoryĪ vast and unprecedented international star-mapping project was initiated in 1887 by Paris Observatory director Amédée Mouchez, who realized the potential of the new dry plate photographic process to revolutionize the process of making maps of the stars. 4 Combination of the Astrographic Catalogue with Hipparcos.