Dante and the early astronomers . ter observations, made with an astrolabe, weremuch more precise; Ptolemy quotes one from Theon ofSmyrna, which states that Mercury was 3° 50 in advanceof the Heart of the Lion (Regulus), and for his ownobservations he also usually gives the sign, degree, andminute. Sometimes the planets had been observed sonear stars that their positions could be very accuratelydetermined by the aid of Hipparchus , on a certain morning in the 13th year ofPtolemy Philadelphus ( 273), saw Venus beside thelast star in the wing of the Virgin (Beta Virg
Dante and the early astronomers . ter observations, made with an astrolabe, weremuch more precise; Ptolemy quotes one from Theon ofSmyrna, which states that Mercury was 3° 50 in advanceof the Heart of the Lion (Regulus), and for his ownobservations he also usually gives the sign, degree, andminute. Sometimes the planets had been observed sonear stars that their positions could be very accuratelydetermined by the aid of Hipparchus , on a certain morning in the 13th year ofPtolemy Philadelphus ( 273), saw Venus beside thelast star in the wing of the Virgin (Beta Virginis); PTOLEMY. 145 Ptolemy himself saw her so close behind a certain starin Aquarius that she seemed to touch it with her rays;and in the 83rd year after the death of Alexander,Jupiter had been observed to eclipse the Southern Ass,that is the southernmost of the pair of stars on eitherside of the little cluster in Cancer which the ancientscalled the Manger. .^ ^.Position of Sunfe/ // apogee as% determined by/^/> Hipparchus \. Fig. 32. The suns Deferent. (Its eccentricity is exaggerated). The sun was much easier to manage than the always in the same direction, he needed noepicycle, and remaining always in the ecliptic, no one irregularity, the varying speed in different partsof the zodiac, which Meton had discovered and Calippusconfirmed, Hipparchus accounted for by placing himon eccentric deferent; Ptolemy adopted this withoutchange, and made the year the same length as Hipparchushad done. As the slowest motion was observed whenthe sun was in the sign of Gemini (at the time of year 146 PTOLEMY, corresponding with the end of our month of May), theeccentric was placed as in the diagram; and the sun,supposed to be revolving uniformly round the centre C,had a slower motion as seen from Earth when he wentnorth, because he was then more distant. We know now that it is really Earth which revolvesround the sun, but the elliptical shape of her orbit isnot
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