Many sixteenth- and seventeenth-century astronomers believed that astronomy had existed before the Flood. It existed in God's mind as an eternal plan, according to which celestial bodies were created and their periods of revolution defined. Further- more, the first people, Adam and his descendants, the biblical patriarchs, had engaged in astronomy. However, there was no consensus among early modern astronomers as to the fate of antediluvian astronomy after the Flood and its relation to their own astronomy. In this article, I present an overview of the various conceptions of ante- diluvian astronomy, to illustrate astronomers' opinions regarding the origin of their science, and how their views gradually changed.The majority of astronomers in the Renaissance, like their contemporaries in other disciplines, believed in the existence of knowledge granted to humans by God at the beginning of history, and held that mankind should seek to return to this ancient knowledge. I call this the approach. Later in the seventeenth century, this conception was slowly replaced by the belief that astronomy is gradually improved in the course of history: the approach. Exploration of the differing approaches to the idea of antediluvian astronomy reveals that the process of replacement of the retrograde approach by the progressivist was difficult and slow. The shift to the idea of astronomical progress, as it is known from the eighteenth century, certainly was not a matter of course, and it called for a change in some of the fundamental metaphysical assumptions relating to the nature of astronomy. In other words, the idea of progress in astronomy was closely related to the abandonment of the belief that astronomy is of divine origin.1. The Idea of Antediluvian AstronomyIdeas on the origin of astronomy and other mathematical sciences in the early modern period were derived mainly from reports by classical authors, most of which stated that Greek mathematical knowledge drew on Egyptian mathematics.' However, as early as in the Hellenistic period, Jewish historians objected to these reports by Greek scholars, and they sought to prove that theirs was the most ancient culture and that all knowledge had originated from their spiritual tradition. In particular, Josephus Flavius (1st century a.D.) fiercely criticised the opinion that the Jews had made no contribution to science, and he presented an impressive genealogy of wisdom provided to mankind by the Hebrews, which had been granted by God's grace.In his work Jewish antiquities, Flavius speaks about Adam's son Seth and his descendants:2[T]hey also discovered the science of the heavenly bodies and their orderly array. Moreover, to prevent their discoveries from being lost to mankind and perishing before they became known - Adam having predicted a destruction of the universe, at one time by a violent fire and at another by a mighty deluge of water - they erected two pillars, one of brick and the other of stone, and inscribed these discoveries on both; so that, if the pillar of brick disappeared in the deluge, that of stone would remain to teach men what was graven thereon and to inform them that they had also erected one of brick. It exists to this day in the land of Seiris.To destroy corrupt mankind, God subsequently sent the Flood, which only Noah and his family survived. After the Flood, astronomical knowledge was passed on, apparently thanks to the pillars along with the knowledge of Noah himself, to Noah's sons, who gradually populated the world, as described in detail by Flavius. Of them, Shem's descendants became the ancestors of the Chaldeans.3 According to Flavius, Abraham, who was well versed in astronomy, came from this Chaldean background. When Abraham visited Egypt, Egyptian priests asked him to introduce them to arithmetic and astronomy, because they had no knowledge of these sciences. Flavius concludes that Greek sages subsequently learnt arithmetic from Egyptian priests and brought the knowledge to Greece. …