Adjusting Astronomical Practices: The “Carte du Ciel”, the democratic rules and the circulation of opinions at the end 19th century

Launched in 1887, the “Carte du Ciel” was an international project aiming at photographing the entirety of the celestial vault. Tasks required for this huge undertaking were divided among 18 observatories around the globe. Instruments were standardized and a series of international conferences established operating modes and prescribed norms to be followed everywhere. In each observatory, however, the drive toward uniformity ran into a variety of minor technical and practical problems. In this paper, we examine the strategies mobilized by observers to tinker with stated rules and adapt them to their own experience as astronomers. To underscore the tension between normative prescriptions and individual practices, we consider the Bulletin of the Permanent International Committee for the execution of the Carte du Ciel as an informal forum where various queries raised and arrangements adopted were shared among the scientific community.