Astrolabe Glossary and Notes


Although the earth’s axis remains inclined 23°27’ from the ecliptic, its direction changes slowly. Over 25,800 years this slow change will describe a complete circle and produces the ‘precession of the equinoxes’. The equinoctial points, the first degrees of Aries and of Libra, drift slowly backwards (westwards) along the equator approximately 1°24’ every century. The precession of the equinoxes has caused the zodiacal constellations to drift one full sign west from their zodiacal signs.
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