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. Furthermore, 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 antediluvian 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 "retrograde 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 "progressivist 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.