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Why did the Carte du Ciel project take so long to complete?

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Astronomical map Star trails over banksia trees, in Gippsland, Vic., Austl. The south celestial pole, located in the constellation Octans, is at the centre of the trails.

The Carte du Ciel project, an ambitious international effort to photographically map the entire sky, took decades to complete because it was initiated with limited technology and an overly complex methodology.12

Devised in 1887, the project required the cooperation of 18 observatories to capture the sky on thousands of small photographic plates, each covering only 2° square. This labor-intensive process, which involved manually measuring star positions, sapped the resources and energy of observatories worldwide for decades.12

The project's duration was further extended because it was planned "all too hastily" before the necessary technical infrastructure for such a massive undertaking was fully mature. Ultimately, the Carte du Ciel remains incomplete in its original form, as 20th-century technical advances rendered the project obsolete by allowing stellar positions to be determined much more efficiently from single photographs covering significantly larger areas of the sky. While the associated Astrographic Catalogue was essentially finished by 1958, the full photographic atlas was never finalized as originally envisioned.21