The Astronomic Observatory of Ambohidempona embodies both in architectural and in functional terms the very expression of Jesuit power in the Malagasy capital. This study examines the degree to which a scientific institute focusing on research in meteorology and astronomy became a power locus in the colonial context. The key interest lies in the period chosen for study, 1889–1923. Jesuit work in Madagascar considerably predates that of the colonizers (1896), because it was motivated by the struggle against Protestants, who were already well implanted. The study shows that the Observatory, by means of its double identity—Jesuit and scientific—was placed at the heart of a network of knowledge production and collaborative projects, which had local, national, and international ramifications.