Climate, Astrology and the Age of the World in Thirteenth-Century Thought; Giles of Lessines and Roger Bacon on the Precession of the Solar Apogee

A sizeable portion of the fourth book of Roger Bacon's Opus majus (c. 1267) is dedicated to demonstrating and vindicating the 'usefulness of athematics in the study of divinity' ('mathematicae in divinis utilitas'). Under the lemma 'On times' ('De temporibus'), Bacon closes in on the various ways in which astronom ical knowledge can assist in the reconstruction of biblical chronology, culminating in a lengthy excursus on the true historical date of Jesus's crucifixion.1 In addition to investigating the date of the Passion, he also deals with various problems of chronology in the Old Testament, including the season in which the world was created. In Bacon's day the general consensus was that the world had been created at the time of the spring equinox; but he also knew of scholars who favoured a creation in autumn, for which they could point to a statement in Josephus ( Jewish Antiquities, 1.81) and a number of scriptural passages which presupposed Tishri/ October as the beginning of the year.2 Having introduced the two positions, Bacon goes on to illuminate their astronomical dimension with the following remarks: