The Changing Heavens
The successive positions of the sun in the heavens during its annual retreat below the eastern horizon in the circle called the ecliptic were mapped out by the ancient priesthoods in milestones corresponding to the twelve months of the year. These milestones, the zodiacal constellations, were groups of stars whose rising and setting positions roughly corresponded to that of the sun at a particular season. Owing to the slow rotation (precession of the equinoxes) of the equinoctial circle about the ecliptic, the sun's position among the fixed stars at a particular season is not the same as it was in ancient times, here shown. When the sun occupies the position of Aries (i.e. is seen in the same direction as Aries would be seen if visible), it sets and rises with the latter, which is therefore invisible. A month later, when the sun is in Taurus, Taurus rises and sets with the sun and is invisible. Aries is seen rising just before sunrise where the sun rose a month earlier. When the sun was in Aries, Taurus would have been setting for about an hour after sunset where the sun would sink below the horizon a month later. The constellations corresponding to the sun's position during the summer months (Taurus and Virgo, Gemini and Leo, Cancer) had northerly risings and settings, describing large arcs and therefore remaining long above the horizon in the winter night sky. The constellations mapping out the sun's position in the winter months (Pisces and Scorpio, Aquarius and Sagittarius, Capricorn) have southerly risings and settings, describing short arcs above the horizoin and being conspicuous during the short summer nights.
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