![]() ![]() He found that Spica was approximately 6° west of the autumnal equinox. Hipparchus measured the ecliptic longitude of the star Spica during lunar eclipses. Hipparchus discovered another gem in his account of his discovery in On the Displacement of the Solsticial and Equinoctial Points, which Ptolemy subsequently described in his Almagest III.1 and VII.2). This apparent drifting backwards from the point of view on Earth is called precession and consists of a cyclic wobbling in the orientation of Earth’s axis of rotation with a period of 25,772 years but instead the point of terrestrial observation. He concluded that it was not the stars that were drifting. ![]() ![]() Upon the compilation of the renowned star catalogue, which he completed in 129 BCE, Hipparchus observed that the positions of the stars had shifted from that recorded in earlier Babylonian (Chaldean) measures. The motion of the equinoxes along the ecliptic is caused by the cyclic precession of Earth’s axis of rotation. In understanding the nature of the sideral zodiac in relation to the tropical, we need to consider the Precession of the Equinoxes. ![]()
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