- Great year
A Great year (also known as a Platonic year or Equinoctial cycle) is the time required for one complete cycle of the
precession of the equinoxes, about 25,765 years, at the current rate. Astrologersconsider it important, while modern day astronomersaccount for precession to determine a star's position but care little about a complete precession cycle. The impact of the precession is raised in discussions of the origins of myths by scholars such as Robert Graves, in his comprehensive work The Greek Myths, who sought those origins from fragments of earlier myths, contained in those from the earliest historical records and prehistoric symbols discovered through archaeology.
Usually in literature one finds the duration of the precession given as 26000 years, being a rounding of the supposedly more accurate value of 25800 years. In reality the exact duration cannot be given, as the speed of the general precession is a value changing over time. This speed is currently 243.8 microradians (50.3
arcseconds) per year which would mean 25765 years for one cycle to complete, but speeds of 243.6 microradians (50.25 arcseconds) and 244.0 microradians (50.34 arcseconds), which would lead to the same rounded value 243.8 microradians would result in 25791 and 25744 years, respectively.
The precessional speed is slightly increasing each year, and therefore the cycle period is decreasing. Numerical simulations of the solar system over a period of millions of years give a period of 257 centuries. [A.L. Berger; Obliquity & precession for the last 5 million years; "Astronomy & astrophysics 51" (1976), 127] but no one is certain of the exact precession rate over long periods of time. Near the turn of the 20th century astronomer Simon Newcomb invented a "constant" to account for the increasing annual precession rate. Over the last 100 years this constant has been found to have underestimated the actual acceleration in the rate.
Most astrologers use a precession rate rounded to 50 arc seconds per year to derive a Great Year period of 25,920 years, the period required for the equinox to move through all twelve of the classic zodiacal signs. Some, such as
Boris Cristoffprefer to round the age of one sign of the zodiac to 2100 years, which equates to a Great Year duration of 25,200 years. The Sanskrit scholar Swami Sri Yukteswarputs the length of a Great Year at 24,000 years, composed of one ascending age of 12,000 years and one descending age of 12,000 years. In India the Great Year is called a Yugacycle.
The Greeks broke the ascending and descending portions of the Great Year into four ages each known as the Iron, Bronze, Silver and Golden Ages. The Indian Yuga cycle also breaks each ascending and descending arc into four periods; the Kali, Dwapara, Treta and Satya yugas.
history of astronomy, a great year may refer to any real or imagined cycle with astronomical or astrological significance. The Greeks sometimes called the period of time required for the naked eye planetsto realign, a great year. It was an important concept in ancient Stoicism.
Giorgio de Santillanathere are over 200 myths or folk stories from over thirty ancient cultures that refer to a Great Year tied to the movement of the equinox or the motion of the heavens.
The book, The Great Year, written by Nicholas Campion describes some of the ancient and modern mythology of the Great Year concept. The documentary film, The Great Year, written by Walter Cruttenden and narrated by James Earl Jones describes some of the archaeological and astronomical evidence for the Great Year.
Discovery of precession
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Great year — Year Year, n. [OE. yer, yeer, [yogh]er, AS. ge[ a]r; akin to OFries. i?r, g?r, D. jaar, OHG. j[=a]r, G. jahr, Icel. [=a]r, Dan. aar, Sw. [*a]r, Goth. j?r, Gr. ? a season of the year, springtime, a part of the day, an hour, ? a year, Zend y[=a]re… … The Collaborative International Dictionary of English
great year — n. one full cycle of precession of the equinoxes, equal to c. 25,800 years … English World dictionary
great year — noun time required for one complete cycle of the precession of the equinoxes, about 25,800 years • Syn: ↑Platonic year • Hypernyms: ↑time period, ↑period of time, ↑period * * * noun Etymology: Middle Eng … Useful english dictionary
great year — Platonic Pla*ton ic, Platonical Pla*ton ic*al, a. [L. Platonicus, Gr. ?: cf. F. platonique.] 1. Of or pertaining to Plato, or his philosophy, school, or opinions. [1913 Webster] 2. Pure, passionless; nonsexual; philosophical. [1913 Webster]… … The Collaborative International Dictionary of English
great year — Astron. See Platonic year. [1905 10] * * * … Universalium
great year — the Platonic year … Dictionary of units of measurement
great year — noun Date: circa 1741 the period of about 25,800 years required for one complete cycle of the equinoxes around the ecliptic … New Collegiate Dictionary
Great Year. — See Magnus Annus. * * * … Universalium
Great Year. — See Magnus Annus … Useful english dictionary
Year — Year, n. [OE. yer, yeer, [yogh]er, AS. ge[ a]r; akin to OFries. i?r, g?r, D. jaar, OHG. j[=a]r, G. jahr, Icel. [=a]r, Dan. aar, Sw. [*a]r, Goth. j?r, Gr. ? a season of the year, springtime, a part of the day, an hour, ? a year, Zend y[=a]re year … The Collaborative International Dictionary of English