Astronomical Images : Thabit's explanation of the motion of the eighth sphere

Peter Apian

Astronomical Images

<p style='text-align: justify;'>This Venetian edition of Peuerbach's <i>Theoricae novae </i>was copied from Apian's 1528 edition, printed in Ingolstadt. Subsequently, the work went through several further editions. Apian's edition added new woodcuts as well as notations to some of those from earlier editions. Some errors in the woodcuts in the 1528 edition were repeated in this Venetian edition of 1537. The <i>Theoricae novae</i> includes explanation of the trepidation of the eighth sphere by Thabit ibn Quarra (ninth-century Assyrian). This section is believed to have been added around 1460. Peurbach reports that Thabit posited two kinds of ecliptic ' one fixed and the other movable, so that the beginnings of the movable Aries and Libra are carried around in two small circles, whose centres of poles are also the beginnings of Aries and Libra of the fixed ecliptic.</p>