Platonic year


Platonic year
   a unit of time used in astronomy. The earth's axis of rotation is not fixed in space; the attraction of the moon causes it to slowly trace out a circle in the sky. This motion, called precession, changes the orientation of the sky as seen from the earth's surface: the poles appear to shift their locations and the sun's point of crossing the equator slowly rotates through the constellations of the Zodiac. The Platonic year is the length of time required for one complete precessional rotation: about 25 800 years. The unit is named for the ancient Greek philosopher Plato (ca. 428-348 BCE). It is sometimes called the great year.

Dictionary of units of measurement. 2015.

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  • Platonic 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

  • Platonic 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

  • Platonic year — n. GREAT YEAR …   English World dictionary

  • Platonic year — noun time required for one complete cycle of the precession of the equinoxes, about 25,800 years • Syn: ↑great year • Hypernyms: ↑time period, ↑period of time, ↑period * * * Astron. a period of about 26,000 years, equal to the time required for a …   Useful english dictionary

  • Platonic year — Astron. a period of about 26,000 years, equal to the time required for a complete revolution of the equinoxes. Also called great year. Cf. precession of the equinoxes. [1630 40] * * * …   Universalium

  • PLATONIC YEAR —    a period of 26,000 years, denoting the time of a complete revolution of the equinox …   The Nuttall Encyclopaedia

  • 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

  • Year and a day — 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

  • Year of grace — 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

  • 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] {Platonic… …   The Collaborative International Dictionary of English


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