What is the Great Year?

In astronomy, the Great Year is one full cycle of the precession of the equinoxes: the slow turning of the sky caused by a wobble in the Earth’s axis. It takes about 25,800 years. Over that time the pole star changes, and the point where the sun stands at the spring equinox slides backward through the constellations of the zodiac, about one sign in 2,150 years. Gerald Massey, in Book IX of Ancient Egypt: The Light of the World (1907), reads the world’s flood stories by this great cycle.

Why the sky shifts: The Earth spins like a tilted top. The pull of the sun and moon on its bulge at the equator makes its axis trace a slow circle, so the point in the sky above the North Pole moves among the stars. When the pyramids were built, the pole lay near Thuban, a star in Draco; today it is near Polaris; in about 12,000 years it will be near Vega. The spring equinox point is still called the First Point of Aries, a name from the time it lay in Aries, though it now lies in Pisces.
Who found it, and Plato’s year: Its discovery is credited to the Greek astronomer Hipparchus, who noticed it in the second century BCE by comparing his star positions with older records. Plato’s “perfect year”, in his dialogue the Timaeus, is a different idea: the time it takes the circuits of the sun, moon, planets and stars all to return together to where they began. Later writers often gave Plato’s name to the precession cycle, but he wrote two centuries before it was known.
The ages of Pisces and Aquarius: The astrological ages come from this cycle. Each is named after the constellation behind the sun at the spring equinox, so the Age of Pisces is said to be giving way to the Age of Aquarius. Their dates are disputed: the constellations differ in size, astrologers do not agree where one ends and the next begins, and estimates for the start of the Age of Aquarius differ by centuries. The ages are astrological ideas, not astronomical facts.
The Great Year in Massey’s reading: In Book IX Massey reads the cycle mainly by the moving pole. He puts the Great Year at about 26,000 years (he also gives 25,868) and counts seven pole stars in it, each holding its place for some 3,714 years. In his reading, when a pole star sank from its place, myth told of a flood, so the world’s deluge stories mark the end of an age in the sky, not a rain on earth. The last, “the great deluge of all”, he puts near 9600 BCE. In Book XI he reads the judgment of Revelation by the same clock.
What scholars say now: Egyptologists find no clear sign that the Egyptians knew of precession or measured it. The twelve signs of the zodiac reached Egypt from Babylonia only in the last centuries BCE. Massey’s long timelines for Egyptian star-lore, reaching back tens of thousands of years, are not accepted: recorded Egyptian history begins about 3100 BCE. The pole moves in a smooth circle, passing near a bright star only now and then, not through seven equal stations. And flood stories are traced to many separate roots, the flood of Genesis to older stories from Mesopotamia.
In Massey’s words: “It is not the ending of the world, but of a great year of the world.” (Gerald Massey, Ancient Egypt: The Light of the World (1907), Book XI, p. 694)
In the app: Library › Book IX. In the app, Book IX gives Massey’s full reading of the Great Year, with the 1907 Star-Map of Precession in its place and a note in plain words under every part.

Last updated October 28, 2026.

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