projected photographic mapping of some 10 million stars in all parts of the sky that was planned to include all stars of the 14th magnitude or brighter and to list in an associated catalog all of the 12th magnitude or brighter. The plan, devised about 1887 by Amédée Mouchez, director of the Paris Observatory, involved the cooperation of 18 observatories located around the world in an attempt to photograph the entire sky on plates, each covering an area only 2° square. Technical advances in the 20th century allowed stellar positions to be accurately determined from single photographs covering much larger areas of the sky, and the Carte du ciel, in which decades of labour were invested, remains incomplete. Its accompanying catalog was essentially finished by 1958.