<p style='text-align: justify;'>Georg Peuerbach (Georgius Aunpekh) was born in Peuerbach, near Linz. He studied at the University of Vienna, obtaining his BA in 1448 and MA in 1453. He held positions as court astrologer to the king of Hungary, and then to Emperor Frederick III. At the request of Cardinal Johannes Bessarion, Peuerbach began an abridgement of Ptolemy's <i>Almagest</i>, which was incomplete when he died in 1461. Peuerbach had also compiled <i>Theoricae novae planetarum</i>, a revision of the <i>Theorica planetarum </i>attributed to Gerard of Cremona. This originated as lectures given in Vienna in 1454, which were attended by Johannes Regiomontanus, who published the first edition in Nuremberg around 1474. This is the 1482 edition by Erhard Ratdolt, which contains copies of the original diagrams. As in the original edition, some woodcuts were coloured. Ratdolt was active in Venice and Augsburg, and was particularly interested in astronomical subjects. He also produced editions of Johannes Engel's <i>Astrolabium planum in tabulis ascendens</i> and G. Julius Hyginus' <i>Poetica astronomica</i>. Peuerbach's text was printed in a compilation that also included Johannes Sacrobosco's <i>Sphaericum opusculum</i> and Johannes Regiomontanus' <i>Contra Cremonensia in planetarum theoricas delyramenta disputationes</i>. This collection of astronomical treatises, and other similar ones, together comprised the main elementary texts available in the late fifteenth century. This woodcut, a slightly reduced copy of a diagram of the original edition of Peuerbach's treatise (c. 1474), shows the four orbs and the epicycle of the Moon. The three interior orbs are similar to the orbs of the Sun: two orbs printed black and a white orb sandwiched between them and divided in two by a circle. The black orbs are said to be 'deformed' (<i>difformes</i>), or 'relatively eccentric' (<i>eccentrici secundum quid</i>), because their two surfaces are not concentric: one of them is concentric with the World, while the other has the same centre as the white sandwiched orb, called the eccentric or deferent of the epicycle of the Moon (<i>deferens epicyclum Lunae</i>), abbreviated as the deferent of the Moon. This white orb is eccentric to the centre of the World on both its inner and outer surfaces - in Peuerbach's terms, it is 'absolutely eccentric' (<i>eccentricus simpliciter</i>). Inside this deferent is a small sphere (<i>sphaerula</i>), the epicycle, to which the body of the Moon is attached. In Peuerbach's terms, it is 'immersed in the depth of the third orb' (<i>profunditati orbis tertii immersa</i>). The centre of the epicycle is on the circle that divides the deferent orb into two equal parts. The epicycle (with the planet attached to it) moves according to the motions of the deferent and has its own circular rotation. The deferent has its own motion and is also subject to the motion of the other (black) orbs. The black orbs are called the deferent orbs of the apogee of the Moon's eccentric, or deferent (<i>orbes augem eccentrici Lunae deferentes</i>), because the apogee (or <i>aux</i>) of the Moon's deferent varies according to their motion; they move together in that the narrower part of the larger orb is always above the wider part of the smaller orb. The outermost orb, coloured green in this woodcut, is concentric to the World, encompassing the other three and revolving around them - in Peuerbach's words, it surrounds the aggregate of the three other orbs (<i>deinde habet orbem mundo concentricum aggregatum ex tribus aliis ambientem</i>). It is called the 'deferent of the Head of the Dragon' (<i>deferens Caput Draconis</i>). The diagram shows the centre of the World (<i>c. mundi</i>) and the centre of the deferent of the Moon (<i>c. deferentis</i>). The line passing through the centre of the World, the centre of the deferent, the points of the deferent that are most distant from the centre of the World (the apogee, or <i>aux</i>), and those that are least distant (the perigee, or <i>oppositum augis</i>), is the axis of the deferent orbs of the apogee. It corresponds to the line called the line of the apogee (<i>linea augis</i>) in the theory of the Sun. The innermost circle on the diagram does not belong to an orb. It is described by the centre of the deferent as it moves around the centre of the World, and is divided in two by the axis of the deferent orbs of the apogee. The point on this axis and on this circle which is opposite to the centre of the deferent is called the 'opposite point' (<i>punctum oppositum</i>).</p>
