Astronomical Images : Orbs, axes and poles of the motion of the superior planets

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 superior planets. The three orbs of the superior planets are seen from above, in latitudinal section: the exterior and interior black 'deformed' orbs (the deferent orbs of the apogee of the eccentric, labelled '<i>deferens augem eccentr[ici] exterior</i>' and '<i>deferens augem eccen[trici] interior</i>'), and the white eccentric orb sandwiched between them (labelled '<i>deferens epicyclum trium superiorum</i>'), with a 'hole' where the axis of the movement of the epicycle is visible. The sections also show that the three orbs do not have the same axis. The sections of the black orbs are in the same plane, perpendicular to the main axis: that of the ecliptic (<i>axis octavae sphaerae</i>), which coincides with the axis of the deferent orbs of the apogee of the eccentric. The section of the white eccentric orb is in a different plane, perpendicular to the other axis: the axis of the eccentric (<i>axis eccentrici</i>). This axis of the eccentric intersects the axis of the ecliptic at a point that does not coincide with the centre of the World. Thus, the former rotates around the latter when it is carried by the motion of the eighth sphere, and the points situated along it and on the circumference of the deferent describe circles parallel to the plane of the ecliptic. Five of these circles are drawn: the two circles described by the poles of the axis of the eccentric; the very small circle described by the centre of the eccentric; the large circle described by the perigee of the eccentric (<i>cir[culus] qui describitur ab auge opposito</i>), and the still larger circle of the apogee (<i>cir[culus] qui describitur ab auge</i>). For a more detailed description of the consequences of the intersection of the axes, see Reinhold (1553), fol. 42r.</p>