Astronomical Images : Orbs, axes and poles of the Sun's motion

Erasmus Oswald Schreckenfuchs

Astronomical Images

<p style='text-align: justify;'>This unique edition of Oswald Schreckenfuchs' massive commentary contained, for the first time in the <i>Theoricae novae</i> printed tradition, a series of three-dimensional diagrams intended to complement the ordinary diagrams of the orbs, circles, axes and poles of the planets and the eighth sphere. These diagrams are printed on one side of two <i>bifolia</i>. In some copies the <i>bifolia</i> form one gathering b (four folios), bound after the preface; in others the figures have been cut, and each is inserted in the appropriate place in the treatise. They are not lettered and have no legend, though some of their elements are labelled, as they must be used in association with the diagrams in the text. This diagram corresponds to the figure of the orbs, axes and poles of the motion of the Sun. The outermost circle represents the ecliptic. The three orbs of the Sun are seen from above, in latitudinal cut: the two black 'deformed' orbs (the deferent orbs of the apogee of the Sun), and the white 'deferent' orb sandwiched between them, which bears the body of the Sun. The only elements of the figure that are labelled are the axis of the ecliptic (<i>axis zodiaci</i>) with its two poles and the axis of the deferent of the Sun (<i>axis deferentis</i>). The diagram shows how, according to Peuerbach, 'the axis of the solar deferent orb with the centre of the eccentric circle, and also the poles of the solar deferent orb, describe the circumferences of small circles about the axis of the deferent orbs of the apogee [that coincides with the axis of the ecliptic], according to the size of their eccentricity', as the axis of the deferent revolves around the axis of the ecliptic. Translated quotations of Peuerbach's <i>Theoricae</i> are from Aiton (1987).</p>