800:
104:
824:
776:
812:
788:
47:, by comparing the position of the vernal equinox against the fixed stars in his time and in earlier observations, discovered that it shifts westward approximately one degree every 72 years. Thus the time it would take the equinox to make a complete revolution through all the zodiac constellations and return to its original position would be approximately 25,920 years. In the
151:
222:
On the diverse motions of the planets the mathematicians have based what they call the Great Year, "which is completed when the sun, moon and five planets having all finished their courses have returned to the same positions relative to one another. The length of this period is hotly debated, but it
267:
Hipparchus discovered that the fixed stars as a whole gradually shifted their position in relation to the annually determined locations of the Sun at the equinoxes and solstices... Otto
Neugebauer argued that Hipparchus in fact believed that this was the maximum figure and that he also computed the
131:
A slow conical motion of the Earth's polar axis about its normal to the plane of the ecliptic is caused by the attractive force of the other heavenly bodies on the equatorial protuberance of the Earth. A similar conical motion can also be observed in a gyroscope that is subjected to lateral forces.
207:
And so people are all but ignorant of the fact that time really is the wanderings of these bodies, bewilderingly numerous as they are and astonishingly variegated. It is none the less possible, however, to discern that the perfect number of time brings to completion the perfect year at that moment
127:
is the plane described by the apparent motion of the Sun against the starry background. It is the Earth's orbital motion about the Sun which causes this apparent motion to occur. The Earth's axis of rotation is not set perpendicular to this plane but at a present angle of 23.5 degrees to the
301:
God afforded them a longer time of life on account of their virtue, and the good use they made of it in astronomical and geometrical discoveries, which would not have afforded the time of foretelling unless they had lived six hundred years; for the great year is completed in that
276:(c. 170 AD), who "adopted the larger, erroneous, figure, with the result that henceforth the two versions of the Great Year — the Platonic Great Year, defined by the planets, and the precessional, defined by the stars — were to be increasingly confused."
320:) determined the cause of precession and established the rate of precession at 1 degree per 72 years, very close to the best value measured today, thus demonstrating the magnitude of the error in the earlier value of 1 degree per century.
51:, the precession can be pictured as the axis of the Earth's rotation making a slow revolution around the normal to the plane of the ecliptic. The position of the Earth's axis in the northern night sky currently almost aligns with the star
139:
and the equinox points in the ecliptic move westward along the ecliptic at the rate of about 50.3 seconds of arc per year as a result. In 25,772 years, the points are once again at the same point in the sky where observations began.
70:
forward or back in time would arrive at a point where they are in the same positions as they are today. He called this time period the Great Year and suggested that such a unified return would take place about every 36,000 years.
282:
has even been accused of committing scientific fraud by making up observations that would give the figure of 36,000 years even though the data available to him were good enough to get very near the true figure of 26,000.
128:
perpendicular. The alignment of the axis is maintained throughout the year so that the point of sky above the north or south poles remains unchanged throughout the Earth's annual rotation around the Sun.
406:
599:
147:, of the Earth's axis is not constant but changes in a cycle of its own. During a cycle that averages about 40,000 years, the tilt of the axis varies between 22.1 and 24.5 degrees.
20:
55:, the North Star. But as the direction of the axis is changing, this is a passing coincidence which was not always so and will not be so again until a Great Year has passed.
208:
when the relative speeds of all eight periods have been completed together and, measured by the circle of the Same that moves uniformly, have achieved their consummation."
251:
The origin of the
Platonic Year would seem to have no connection with the precession of the equinoxes as this was unknown in Plato's time. Two centuries after Plato,
368:
414:
461:
182:. The cycle which Plato describes is one of planetary and astral conjunction, which can be postulated without any awareness of axial precession.
603:
94:
The difficulty with the term "great year" lies in its ambiguity. Almost any period can be found sometime or somewhere honored with this name.
632:
Nicholas
Campion, "The Great Year: Astrology, Millenarianism and History in the Western Tradition" (Arkana/Penguin Books, 1994), p. 246–247.
259:, and the term "Great Year" eventually came to be applied to the period of that precession caused by the slow gyration of the Earth's axis.
623:
Nicholas
Campion, "The Great Year: Astrology, Millenarianism and History in the Western Tradition" (Arkana/Penguin Books, 1994), p.246.
525:
Nicholas
Campion, "The Great Year: Astrology, Millenarianism and History in the Western Tradition" (Arkana/Penguin Books, 1994), p. 6.
188:(c. 120 BC) is the first Greek credited with discovering axial precession roughly two hundred years after Plato's death (see below).
23:
The tilt of the Earth's polar axis remains constant but describes a circular path in space during a period known as The Great Year.
562:
505:
479:
111:
projected on the sky is a circle which takes 25,772 years to complete. The data in red show the polar point in past
244:
reckoned a Great Year as 2484 years: but it has been argued that this is a miscopying of 2434, which represents 45
31:
has more than one major meaning. It is defined by scientific astronomy as "The period of one complete cycle of the
194:(1st century BC) followed Plato in defining the Great Year as a combination of solar, lunar and planetary cycles.
372:
755:
727:
849:
589:
William Harris Stahl, "Macrobius: Commentary on the Dream of Scipio" (Columbia
University Press, 1952), p. 21
435:
317:
844:
854:
766:
256:
471:
290:
178:(circle of the Same) to their original positions; there is no evidence he had any knowledge of
682:
552:
124:
241:
62:, which is also called the Great Year, has a different more ancient and mystical meaning.
8:
859:
828:
166:(c. 360 BC) used the term "perfect year" to describe the return of the celestial bodies (
864:
816:
804:
199:
136:
48:
154:
The precession of the axis of a spinning body as seen on a small scale in a gyroscope.
751:
723:
657:
642:
558:
475:
231:
112:
67:
780:
715:
499:
467:
335:
329:
214:
179:
339:
87:
748:
The Shape of
Ancient Thought: Comparative Studies in Greek and Indian Philosophy
869:
171:
75:
310:(c. 3rd century BC) who reckoned time in intervals of 60, 600 and 3600 years.
838:
272:
It is argued that a confusion between the two originated with the astronomer
708:
Annus
Platonicus, A Study of World Cycles in Greek Latin and Arabian Sources
792:
332: – Time period in ancient historical and astrological theories of time
313:
268:
true rate of one complete precession cycle at just under 26,000 years...
264:
252:
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185:
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234:
states that 'the philosophers' reckon the Great Year as 15,000 years.
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658:
Josephus – Antiquities of the Jews – Book I, Chapter 3, Paragraph 9
578:
307:
286:
74:
By extension, the term "Great Year" can be used for any concept of
66:
hypothesized that winding the orbital motions of the Sun, Moon and
36:
103:
554:
Stars, Mind & Fate: Essays in
Ancient and Mediaeval Cosmology
279:
273:
197:
Plato's description of the perfect year is found in his dialogue
116:
52:
40:
191:
167:
577:
Aristarchos & System B 2002, DIO 11.1 May 31 (p. 6)
163:
63:
746:
Mcevilley, Thomas C. (2001). "Chapter 3: The Cosmic Cycle".
19:
345:
338: – Change of rotational axis in an astronomical body (
175:
787:
263:
Some time around the middle of the second century BC, the
407:"Aerospace Science and Technonlogy Dictionary P Section"
600:"Aerospace Science and Technology Dictionary G Section"
369:"Aerospace Science and Technology Dictionary G Section"
306:
It has been suggested that he obtained this value from
230:(early fifth century AD) in his commentary on Cicero's
764:
506:"Full text with an English translation by H. Rackham"
653:
651:
135:The resultant motion of the Earth's axis is called
836:
648:
223:must necessarily be a fixed and definite time."
737:Cristoff, Boris (1981). Roca, Martínez (ed.).
710:. Louvain: l'Institut Orientaliste de Louvain.
158:
626:
534:Plato, Timaeus 39d, in John M. Cooper (ed.),
493:
491:
289:(first century AD) refers to a 'Great Year' (
98:
255:is credited with discovering the period of
550:
546:
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538:(Hackett Publishing Company, 1997), p. 1243
394:A History of Ancient mathematical astronomy
617:
488:
745:
602:. Hq.nasa.gov. 1989-10-18. Archived from
472:10.1093/acprof:oso/9780199557660.001.0001
371:. Hq.nasa.gov. 1989-10-18. Archived from
736:
705:
541:
149:
102:
18:
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643:The Authenticity of Ptolemy's star data
519:
837:
635:
579:Comments on the Aristarchan Evidence
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363:
361:
557:. Bloomsbury Academic. p. 96.
13:
699:
14:
881:
358:
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786:
774:
685:. Fordham.edu. p. letter 17
741:. Barcelona: colección Fontana.
675:
662:
592:
583:
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683:"Internet History Sourcebooks"
528:
453:
428:
399:
386:
348: – Age or era in Hinduism
1:
352:
460:Wood, Michael (2010-06-24).
240:(3rd century AD) wrote that
39:, or about 25,800 years".
7:
466:. Oxford University Press.
340:Precession § Astronomy
323:
159:History of both definitions
10:
886:
739:El destino de la humanidad
294:
115:and the constellation the
99:Description of the science
43:reported that his teacher
440:earthobservatory.nasa.gov
143:In addition the tilt, or
706:Callatay, G. de (1996).
536:"Plato: Complete Works"
436:"Milutin Milankovitch"
392:Neugebauer O., (1975)
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270:
225:
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174:rotation of the fixed
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120:
96:
24:
299:
261:
220:
205:
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125:plane of the ecliptic
106:
92:
22:
850:History of astrology
551:J. D. North (1989).
242:Aristarchus of Samos
119:was in at that time.
845:Astronomical epochs
672:, Loeb, p.1, note a
396:, Birkhäuser, p.618
670:Jewish Antiquities
257:equinox precession
156:
137:general precession
121:
49:heliocentric model
25:
855:Astrological ages
716:Campion, Nicholas
564:978-0-907628-94-1
463:The Platonic Year
232:Somnium Scipionis
68:naked eye planets
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413:. Archived from
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336:Axial precession
330:Astrological age
297:) of 600 years.
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215:De Natura Deorum
180:axial precession
107:The path of the
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218:, Cicero wrote
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88:Otto Neugebauer
78:in the world's
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720:The Great Year
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295:μέγας ἐνιαυτός
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117:vernal equinox
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76:eternal return
16:Length of time
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641:R.R.Newton, "
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606:on 2005-04-21
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60:Platonic Year
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34:
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21:
829:Solar System
750:. Allworth.
747:
738:
719:
707:
687:. Retrieved
677:
669:
664:
637:
628:
619:
608:. Retrieved
604:the original
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535:
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510:. Retrieved
498:
462:
455:
444:. Retrieved
442:. 2000-03-24
439:
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419:. Retrieved
415:the original
410:
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393:
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377:. Retrieved
373:the original
314:Isaac Newton
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86:. Historian
84:philosophies
73:
59:
57:
28:
26:
817:Outer space
805:Spaceflight
722:. Penguin.
80:mythologies
35:around the
860:Precession
839:Categories
757:1581152035
729:0140192964
689:2014-03-02
668:Josephus,
610:2015-08-23
512:2019-11-13
446:2019-02-15
421:2019-02-09
379:2014-03-02
353:References
265:astronomer
253:Hipparchus
238:Censorinus
186:Hipparchus
170:) and the
109:North Pole
45:Hipparchus
29:Great Year
865:Equinoxes
781:Astronomy
302:interval.
246:Exeligmos
228:Macrobius
145:obliquity
33:equinoxes
27:The term
718:(1994).
497:Cicero,
324:See also
316:(1642 –
308:Berossos
287:Josephus
248:cycles.
90:writes:
37:ecliptic
767:Portals
503:II.51.
318:1726/27
280:Ptolemy
274:Ptolemy
200:Timaeus
172:diurnal
168:planets
53:Polaris
41:Ptolemy
754:
726:
561:
508:. 1933
478:
192:Cicero
113:epochs
870:Plato
793:Stars
176:stars
164:Plato
64:Plato
752:ISBN
724:ISBN
559:ISBN
476:ISBN
346:Yuga
203::
123:The
58:The
468:doi
212:In
82:or
841::
650:^
543:^
490:^
474:.
438:.
409:.
360:^
293::
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760:.
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