Voltaire's Great Year - © Dr Shepherd Simpson

The length of a Great Year year equals 25 925 years. [2002 AD] This assumes that the rate of Precession of the Earths' Axis was the same in the past, and will be the same in the future, as it is now. The Great Year is also frequently known as the 'Platonic' Year.

Voltaire, Newton and the Great Year: One of the earliest mentions we have of the concept of a Great Year occurs in the writings of Voltaire [1694 - 1778 AD], looking back to the earlier work of Isaac Newton [1643 - 1727 AD]. Voltaire also mentions the concept of what we would now call the 'Platonic' Month, though as yet it does not possess that name.

Voltaire [Francois Marie Arouet], Lettres Philosophiques, c. 1778: You know that the earth, besides its annual motion which carries it round the sun from west to east in the space of a year, has also a singular revolution which was quite unknown till within these late years. Its poles have a very slow retrograde motion from east to west, whence it happens that their position every day does not correspond exactly with the same point of the heavens. This difference which is so insensible in a year, becomes pretty considerable in time; and in threescore and twelve years the difference is found to be of one degree, that is to say, the three hundred and sixtieth part of the circumference of the whole heaven. Thus after seventy-two years the colure of the vernal equinox which passed through a fixed star, corresponds with another fixed star. Hence it is that the sun, instead of being in that part of the heavens in which the Ram was situated in the time of Hipparchus, is found to correspond with that part of the heavens in which the Bull was situated; and the Twins are placed where the Bull then stood. All the signs have changed their situation, and yet we still retain the same manner of speaking as the ancients did. In this age we say that the sun is in the Ram in the spring, from the principle of condescension that we say that the sun turns round.

Hipparchus was the first among the Greeks who observed some change in the constellations with regard to the equinoxes, or rather who learnt it from the Egyptians. Philosophers ascribed this motion to the stars; for in those ages people were far from imagining such a revolution in the earth, which was supposed to be immovable in every respect. They therefore created a heaven in which they fixed the several stars, and gave this heaven a particular motion by which it was carried towards the east, whilst that all the stars seemed to perform their diurnal revolution from east to west. To this error they added a second of much greater consequence, by imagining that the pretended heaven of the fixed stars advanced one degree eastward every hundred years. In this manner they were no less mistaken in their astronomical calculation than in their system of natural philosophy. As for instance, an astronomer in that age would have said that the vernal equinox was in the time of such and such an observation, in such a sign, and in such a star. It has advanced two degrees of each since the time that observation was made to the present. Now two degrees are equivalent to two hundred years; consequently the astronomer who made that observation lived just so many years before me. It is certain that an astronomer who had argued in this manner would have mistook just fifty-four years; hence it is that the ancients, who were doubly deceived, made their great year of the world, that is, the revolution of the whole heavens, to consist of thirty-six thousand years. But the moderns are sensible that this imaginary revolution of the heaven of the stars is nothing else than the revolution of the poles of the earth, which is performed in twenty-five thousand nine hundred years. It may be proper to observe transiently in this place, that Sir Isaac, by determining the figure of the earth, has very happily explained the cause of this revolution.

All this being laid down, the only thing remaining to settle chronology is to see through what star the colure of the equinoxes passes, and where it intersects at this time the ecliptic in the spring; and to discover whether some ancient writer does not tell us in what point the ecliptic was intersected in his time, by the same colure of the equinoxes.

Clemens Alexandrinus informs us, that Chiron, who went with the Argonauts, observed the constellations at the time of that famous expedition, and fixed the vernal equinox to the middle of the Ram; the autumnal equinox to the middle of Libra; our summer solstice to the middle of Cancer, and our winter solstice to the middle of Capricorn.

A long time after the expedition of the Argonauts, and a year before the Peloponnesian war, Methon observed that the point of the summer solstice passed through the eighth degree of Cancer.

Now every sign of the zodiac contains thirty degrees. In Chiron's time, the solstice was arrived at the middle of the sign, that is to say to the fifteenth degree. A year before the Peloponnesian war it was at the eighth, and therefore it had retarded seven degrees. A degree is equivalent to seventy-two years; consequently, from the beginning of the Peloponnesian war to the expedition of the Argonauts, there is no more than an interval of seven times seventy-two years, which make five hundred and four years, and not seven hundred years, as the Greeks computed. Thus in comparing the position of the heavens at this time with their position in that age, we find that the expedition of the Argonauts ought to be placed about nine hundred years before Christ, and not about fourteen hundred; and consequently that the world is not so old by five hundred years as it was generally supposed to be. By this calculation all the eras are drawn nearer, and the several events are found to have happened later than is computed. I don't know whether this ingenious system will be favorably received; and whether these notions will prevail so far with the learned, as to prompt them to reform the chronology of the world. Perhaps these gentlemen would think it too great a condescension to allow one and the same man the glory of having improved natural philosophy, geometry, and history. This would be a kind of universal monarchy, with which the principle of self-love that is in man will scarce suffer him to indulge his fellow-creature; and, indeed, at the same time that some very great philosophers attacked Sir Isaac Newton's attractive principle, others fell upon his chronological system. Time, that should discover to which of these the victory is due, may perhaps only leave the dispute still more undetermined.

[As can be seen above, over two centuries ago, Voltaire was already confusing the position of the Vernal Equinox Point against the Constellations with that against Tropical Zodiac signs possessing 30° of length each. In contrast Newton does not: talking of Constellations, and not mentioning a Great Year.]

Isaac Newton, The Introduction. Of the Chronology of the First Ages [a draft manuscript of Chronology of Ancient Kingdoms Amended, 1728 AD], p 101 - 102: The first month of the Lunisolar year began sometimes a week or fortnight before the Equinox & sometimes as much after it. And this gave occasion to the first Astronomers who formed the Asterisms to place the Equinox & Solstices in themiddle of the Constellations of Aries Cancer Chelæ & Capricorn. Achilles Tatius tells us that some anciently placed the Solstice in the beginning of Cancer, others in the eighth degree of Cancer others about the twelft degree & others about the 15th degree. This variety of opinions proceeded from the præcession of the Equinox then not known to the Greeks. When the sphere was first formed the Equinox was in the 15th degree or middle of the constellation of Cancer. Then it came into the 12th 8th &1st degree successively. Eudoxus in describing the sphere of the ancients placed the Solstices & Equinoxes in the middle of the Constellations of Aries Chelæ Cancer & Capricorn as is affirmed by Hipparchus Bithynus, & appears also by the description of the Equinoctial & Tropical circles in Aratus who copied after Eudoxus, & by the positions of the Colures of the Equinoxes & Solstices which in the sphere of Eudoxus described by Hipparchus went through the middle of those Constellations. Now Chiron the Master of Iason the Argonaut delineated οχέματα ’ολύμπου the Asterisms as the ancient author of Gigantomachia cited by Clemens Alexandrinus informs us. And Musæus the master of Orpheus & one of the Argonauts made a sphere & is reputed the first among the Greeks who made one. And the sphære it self shews that it was designed in the time of the Argonautic Expedition. ffor that expedition is delineated in the Asterisms with several other ancienter histories of the Greeks: but nothing later then that expedition is delineated there. It seems therefore to have
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been formed by Chiron & Musæus for the use of the Argonauts. For the ship Argo was the first long ship built by the Greeks. Hitherto they had kept to the shore in round vessels of burden with out sails & now upon an Embassy [to the Princes subject to Egypt] they were to sail with expedition through the deep & guide their ship by the stars. The people of the Island Corcyra attributed the invention of the sphere to Nausicae the daughter of Alcinous king of the Pheaces in that Island & its most probable that she had it from the Argonauts who in their return home sailed to that Island & made some stay there with her father. At that time therefore the solstice was reputed in the fifteenth degree of the constellation of Cancer. Afterwards when Pherecides the Astronomer observed the Solstice in the Island Cyrus & his disciple Thales wrote a book of the Tropicks & Equinoxes it was found in the 12th degree of that signe. And at length in order to publish the Lunar Cycle of 19 years Meton & Euctemon observed the solstice in the year of Nabonassar 316, & Columella tells us that they placed it in the eighth degree of Cancer which is seven degrees backwarder then at first. Now the Equinox goes backward one degree in 72 years & seven degrees in 504 years. Subduct those years from the 316th year of Nabonassar, & the Argonautic Expedition will fall upon the 45th year after the death of Solomon, or thereabouts. And the Trojan war was one generation later, several captains of the Greeks in that war being sons of the Argonauts. And the ancient Greeks recconed Memnon or Amenophis to be contemporary to that war feigning him to be the son of Tithonus the elder brother of Priam. Amenophis was therefore of the same age with the elder children of Priam In the last year of the Trojan war he was with his army at Susa according to the ancient Greeks. After that he might return into Egypt & adorn it with Buildings Obelisks & Statues & dye there about 90 or 100 years after the death of Solomon, when he had determined & setled the length of the Egyptian year of 365 days so as to deserve the monument above mentioned in memory thereof

Voltaire's Great Year [c 1778 AD]