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Astronomical Images : Orbs of Venus

Georg von Peuerbach

Astronomical Images

<p style='text-align: justify;'>This 1515 Parisian edition, which contained the commentaries on Peuerbach by Franciscus Capuanus (first edition 1495) and Sylvester de Prierio (first edition 1514), and Jacques Lefevre d'Etaples' <i>Astronomicon</i>, was supervised by Oronce Fine, who redrew and improved all the diagrams of the preceding editions. Folio 32r belongs to the first part of the volume that contains the commentary of Franciscus Capuanus, professor in Padua, first printed in Venice by Simone Bevilaqua in 1495. Its abundant illustration exerted an influence on the subsequent printed tradition of Peuerbach's treatise. In the original (c. 1474) edition of the <i>Theoricae novae</i>, and in the first editions of the commentary by Capuanus (1495 and 1499), no diagram is specifically devoted to Venus. In the original treatise, the figure of the orbs of the superior planets is simply labelled <i>Theorica trium superiorum et Veneris</i>, as it applies also to Venus. Oronce Fine, in his edition of the Capuanus commentary, was the first to illustrate the short chapter, <i>De Venere</i>. This is the second diagram of the chapter (the first is on the preceding page, fol. 31v). It is a simple repetition of the first diagram of the chapter on the three superior planets (fol. 24v). It was later reused in Fine's edition of the <i>Theoricae novae</i> (Paris, 1525), both in the chapter on Venus and in the chapter on the three superior planets. It was probably influenced by a figure in Gregor Reisch's <i>Margarita philosophica</i>, sig. Q8v in our 1512 edition. Venus has three orbs, similar to the orbs of the superior planets. The outermost orb, printed black, is said to be 'deformed' (its two surfaces are not concentric): its exterior convex surface is concentric with the World, while the centre of its concave surface is the centre of the eccentric deferent. The innermost orb, printed black, is also 'deformed': the centre of its interior concave surface is the centre of the World, while the centre of its exterior convex surface is the centre of the eccentric deferent. These two deformed orbs are the deferent orbs of the apogee (<i>orbes augem deferentes</i>). The white orb sandwiched between these orbs is eccentric to the centre of the World on both its inner and outer surfaces. The centre of the epicycle is attached to the circle in the middle of this eccentric orb. The body of the planet is also shown: not as a point on the circumference of the epicycle, as usual, but as a small circle near that circumference. The outermost circle probably represents the ecliptic. As in the case of the superior planets, the movement in longitude of the centre of the epicycle of Venus is not regular in relation to the centre of the eccentric, but to the centre of another circle, the eccentric equant. This centre is situated on the line of the apogee (or the axis of the deferent orbs of the apogee), as the centre of the World and the centre of the eccentric; it is as distant from this centre of the eccentric as the centre of the eccentric is distant from the centre of the World. The eccentric equant, intersecting with the eccentric deferent, has been drawn and the three centres are marked by three dots, labelled '<i>c. aequantis</i>', '<i>c. eccen[trici]</i>', '<i>c. mundi</i>' (each label preceded by a minuscule circle, perhaps a reduplication of the dots). In the original version of the diagram (the <i>Theorica trium superiorum et Veneris</i> of the first edition), the equant circle is not drawn. It was added in 1503, in Reisch's <i>Margarita philosophica</i>. For a three-dimensional representation of the orbs of Venus, see Erasmus Oswald Schreckenfuchs' <i>Commentaria in novas theoricas planetarum Georgii Purbachii</i> (Basel: Henricus Petri, 1556), plate after p. 180.</p>

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