However, this position (that the equinox had moved) was the end result of a long process that was intimately bound up in Hipparchus’s determination of the difference between the tropical year and the sidereal year. Toomer* that Hipparchus concluded, at least at one point in his reasoning, that the equinox had moved (which is actually what had happened), and thus that it cannot be regarded as a fixed point on the ecliptic into perpetuity. Specifically he noted that Spica, the brightest star in Virgo, was observed eight degrees east of the autumnal equinox 150 years before his time, but only six degrees east of the autumnal equinox in his own time (which is a westward motion of the equinoxes). By comparing his own contemporary observations of stars with older positions of the same stars, Hipparchus noted a difference in their distances from the equinoxes.
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