Astronomical Images : Parallax

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 left-hand woodcut shows that the parallax of a star is the arc of the great circle that passes through the zenith and the true position of the star intercepted between the true (defined by a line from the centre of the World through the body of the star) and apparent (defined by a line from the surface of Earth through the body of the star) positions of the star, namely KL, NO and HI. The true and apparent positions coincide when directly overhead (BC). The significance of the diagonal from G is unclear; there is nothing relating to it in the text, and there is nothing like it in the corresponding figure from Peuerbach's <i>Theoricae novae planetarum</i> (Nuremberg, 1473; f. 13v). The right-hand woodcut shows the parallax of a star in latitude. It is an arc of the great circle that passes through the poles (D) of the zodiac and the true position of the star that is intercepted between the two circles parallel to the ecliptic, of which one passes through the true position of the star and the other through its apparent position.</p>