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Astronomical Images : Line of mean motion of the superior planets

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 preceding diagrams (fols. 14v-15r) illustrate the definition of the true and mean apogees of the epicycle of a superior planet; this one accompanies the definitions of its line of mean motion or longitude. It has no model in the original (c. 1474) edition of Peuerbach's treatise. According to Peuerbach, the 'line of mean motion or longitude of the planet or epicycle is that drawn from the centre of the World to the zodiac parallel to the line going from the centre of the equant to the centre of the epicycle' (<i>Linea medii motus planetae vel epicycli est quae a centro mundi ad zodiacum protrahitur lineae exeunti a centro aequantis ad centrum epicycle aequidistans</i>). As in all the diagrams of the same series (fols. 13r-15r), the equant point is misplaced; it ought to be placed above the centre of the deferent and not beneath it, as the centre of eccentric deferent is in the exact middle between the centre of the World and this centre of the equant, all three centres being aligned on the line of the apogee. Translated quotations of Peuerbach's <i>Theoricae</i> are from Aiton (1987).</p>


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