Dante and the early astronomers . geless, changes may occur, and in order that eventhe least of these should not pass unnoticed, he setto work to note the number, brightness, and positionof all he could see. This great catalogue of 1080 stars,copied by Ptolemy in his Almagest, was the basisfor all succeeding catalogues, from Spain to Turkestan,until quite modern times. In it, for the first time,the places of the stars were not merely described 124 HIPPARGHU8. according to their position in the constellation figures,but were noted in degrees on the sphere, as is doneto-day. One day, when compar
Dante and the early astronomers . geless, changes may occur, and in order that eventhe least of these should not pass unnoticed, he setto work to note the number, brightness, and positionof all he could see. This great catalogue of 1080 stars,copied by Ptolemy in his Almagest, was the basisfor all succeeding catalogues, from Spain to Turkestan,until quite modern times. In it, for the first time,the places of the stars were not merely described 124 HIPPARGHU8. according to their position in the constellation figures,but were noted in degrees on the sphere, as is doneto-day. One day, when comparing his notes with those ofTimocharis, who had worked at Alexandria about aTimocharis century and a half earlier, he found that thec. 280. brilliant star Spica, the Ear-of-Corn whichthe Virgin carries in her hand, had apparently movednearer to the autumnal equinox by about 2°. (Twodegrees is about four times the angular diameter ofthe sun). Of course he or Timocharis might havemade a mistake, or Spica might really be moving. Fig. 24. The morement of Spica. among the stars, or she might be carried along withthe rest by a slow movement of the whole Hipparchus satisfied himself that he couldrely upon Timocharis observation, and took painsto verify his own; the second hypothesis could bedisproved by the fact that Spica does not changeher place perceptibly among her neighbours; andfinally it became clear that her motion is part of aslow apparent movement of the whole heavens. Here was a discovery of first importance, an un-expected reward of patient accuracy, of which the i HIPPARCHUS. 125 white Spica, flashing down from summer skies, mayalways remind us. Hipparchus had discovered thegrand cycle which we call the Precession of theEquinoxes, and before Spica returns to the sameposition in which he saw her then, when she ledhim to his great discovery, she will have been watchedby generations of astronomers for another twenty-fourthousand years. No notice o
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