Aristarchus of Samos: The First Heliocentric Theory

Sir Thomas Heath

From Sir Thomas Heath, Aristarchus of Samos (Oxford: Oxford University Press, 1913),pp. 301–302, 304–305. By permission of the Oxford University Press.

There is not the slightest doubt that Aristarchus was the first to put forward the heliocentric hypothesis. Ancient testimony is unanimous on the point, and the first witness is Archimedes, who was a younger contemporary of Aristarchus, so that there was no possibility of a mistake. Copernicus himself admitted that the theory was attributed to Aristarchus, though this does not seem to be generally known. Thus Schiaparelli quotes two passages from Copernicus’s work in which he refers to the opinions of the ancients about the motion of the earth. One is in the dedicatory letter to Pope Paul III, where Copernicus mentions that he first found out from Cicero that one Nicetas (i.e. Hicetas) had attributed motion to the earth, and that he afterwards read in Plutarch that certain others held that opinion; he then quotes the Placita, according to which "Philolaus the Pythagorean asserted that the earth moved round the fire in an oblique circle, in the same way as the sun and moon." The other passage is in Book I, c. 5, where, after an allusion to the views of Heraclides, Ecphantus, and Nicetas (Hicetas), who made the earth rotate about its own axis at the centre of the universe, he goes on to say that it would not be very surprising if any one should attribute to the earth another motion besides rotation, namely revolution in an orbit in space; ’atque etiam (terram) pluribus motibus vagantem et unam ex astris Philolaus Pythagoricus sensisse fertur, Mathematicus non vulgaris.’ Here, however, there is no question of the earth revolving round the sun, and there is no mention of Aristarchus. But it is a curious fact that Copernicus did mention the theory of Aristarchus in a passage which he afterwards suppressed: "Credibile est hisce similibusque causis Philolaum mobilitatem terrae sensisse, quod etiam nonnulli Aristarchum Samium ferunt in eadem fuisse sententia."

I will now quote the whole passage of Archimedes in which the allusion to Aristarchus’s heliocentric hypothesis occurs, in order to show the whole context [Arenarius, I., 4–7].

"You are aware ["you" being King Gelon] that ’universe’ is the name given by most astronomers to the sphere, the centre of which is the centre of the earth, while its radius is equal to the straight line between the centre of the sun and the centre of the earth. This is the common account (ta grafomena), as you have heard from astronomers. But Aristarchus brought out a book consisting of certain hypotheses, wherein it appears, as a consequence of the assumptions made, that the universe is many times greater than the ’universe’ just mentioned. His hypotheses are that the fixed stars and the sun remain unmoved, that the earth revolves about the sun in the circumference of a circle, the sun lying in the middle of the orbit, and that the sphere of the fixed stars, situated about the same centre as the sun, is so great that the circle in which he supposes the earth to revolve bears such a proportion to the distance of the fixed stars as the centre of the sphere bears to its surface. Now it is easy to see that this is impossible; for, since the centre of the sphere has no magnitude, we cannot conceive it to bear any ratio whatever to the surface of the sphere. We must, however, take Aristarchus to mean this: since we conceive the earth to be as it were the centre of the universe, the ratio which the earth bears to what we describe as the universe is equal to the ratio which the sphere containing the circle in which he supposes the earth to revolve bears to the sphere of the fixed stars. For he adapts the proofs of the phenomena to a hypothesis of this kind, and in particular he appears to suppose the size of the sphere in which he makes the earth move to be equal to what we call the ’universe’."

We shall come hack to the latter part of this passage; at present we are concerned only with the italicized words. The heliocentric hypothesis is stated in language which leaves no room for dispute as to its meaning. The sun, like the fixed stars, remains unmoved and forms the centre of a circular orbit in which the earth revolves round it; the sphere of the fixed stars has its centre at the centre of the sun.

Our next evidence is a passage of Plutarch:

"Only do not, my good fellow, enter an action against me for impiety in the style of Cleanthes, who thought it was the duty of Greeks to indict Aristarchus of Samos on the charge of impiety for putting in motion the Hearth of the Universe, this being the effect of his attempt to save the phenomena by supposing the heaven to remain at rest and the earth to revolve in an oblique circle, while it rotates, at the same time, about its own axis." [De facie in orbe lunae ch. VI. 922F-923A.]

Here we have the additional detail that Aristarchus followed Heraclides in attributing to the earth the daily rotation about its axis; Archimedes does not state this in so many words, but it is clearly involved by his remark that Aristarchus supposed that the fixed stars as well as the sun remain unmoved in space. When Plutarch makes Cleanthes say that Aristarchus ought to be indicted for the impiety of ’putting the Hearth of the Universe in motion’, he is probably quoting the exact words used by Cleanthes, who doubtless had in mind the passage in Plato’s Phaedrus where "Hestia abides alone in the House of the Gods." A similar expression is quoted by Theon of Smyrna from Dercyllides, who "says that we must suppose the earth, the Hearth of the House of the Gods according to Plato, to remain fixed, and the planets with the whole embracing heaven to move, and rejects with abhorrence the view of those who have brought to rest the things which move and set in motion the things which by their nature and position are unmoved, such a supposition being contrary to the hypotheses of mathematics"; the allusion here is equally to Aristarchus, though his name is not mentioned. A tract ’Against Aristarchus’ is mentioned by Diogenes Laertius among Cleanthes’ works; and it was evidently published during Aristarchus’s lifetime (Cleanthes died about 232 B.C.).

Other passages bearing on our present subject are the following.

"Aristarchus sets the sun among the fixed stars and holds that the earth moves round the sun’s circle (i.e. the ecliptic) and is put in shadow according to its (i.e. the earth’s) inclinations." [Aeuml;t. II. 24.8]

One of the two versions of this passage has "the disc is put in shadow," and it would appear, as Schiaparelli says, "that the words ’the disc’ were interpolated by some person who thought that the passage was an explanation of solar eclipses." It is indeed placed under the heading "Concerning the eclipse of the sun"; but this is evidently wrong, for we clearly have here in the concisest form an explanation of the phenomena of the seasons according to the system of Copernicus.

"Yet those who did away with the motion of the universe and were of opinion that it is the earth which moves, as Aristarchus the mathematician held, are not on that account debarred tom having a conception of time." [Sextus Empiricus, Adv. Math. X, 174]"Did Plato put the earth in motion, as he did the sun, the moon, and the five planets, which he called the instruments of time on account of their turnings, and was it necessary to conceive that the earth "which is globed about the axis stretched from pole to pole through the whole universe" was not represented as being held together and at rest, but as turning and revolving (streoouenhn koi aneiloumenhn), as Aristarchus and Seleucus afterwards maintained that it did, the former stating this as only a hypothesis (upotiqemenoV monon), the latter as a definite opinion (koi apsoainomenoV)?" [Plutarch, Plat. quaest, VIII, 1, 1006C]"Seleucus the mathematician, who had written in opposition to the views of Crates, and who himself too affirmed the earth’s motion, says that the revolution (periotrooh) of the moon resists the rotation [and the motion] of the earth, and, the air between the two bodies being diverted and falling upon the Atlantic ocean, the sea is correspondingly agitated into waves." [Aeuml;t. III, 17.9]