Aristarchus

Aristarchus of Samos (ca. 310-230 BC) and others proposed that the sun was motionless in the center of an infinitely large sphere of fixed stars, and that the earth revolved about it, as well as rotating about its axis. The story is told in Sir Thomas Heath's Greek Astronomy (1932, New York: Dover, republished 1991) and Aristarchus of Samos, the Greek Copernicus (1913). The lack of an adequate theory of motion and inertia caused the usual view of a fixed earth to prevail. The arguments are given by Ptolemy in the Syntaxis, demonstrating quite clearly that reason alone leads to error.

Aristarchus also estimated the distances of the sun and moon from the earth. The measurements were not accurate enough to give a correct result, but did show that the sun was much more distant than the moon. Eratosthenes, somewhat later, estimated the radius of the earth, obtaining a value that happened to be accurate, although his estimate was thought too large (which encouraged Columbus). These accomplishments are of the greatest significance, as we can see from our perspective. No other science or religion in history came within miles of a similar understanding.

Archimedes discusses Aristarchus in his Sand-Reckoner. A full account is given by Heath, but the Greek text of what he said Aristarchus did is shown here. It is in the Doric dialect, which is interesting, and Attic equivalents are given in square brackets for those unfamiliar with Doric peculiarities, the most common of which is the substitution of a for h .

[Greek Text]

A translation is: Aristarchus of Samos proposed certain hypotheses in writing, from which it followed that the universe was much larger than is now commonly believed. He proposed that the firmament and the sun were unmoving, and the earth described a circle about the sun, which was located at the centre of the orbit, and that the sphere of the fixed stars was as great relative to the orbit of the earth as a sphere is to its center.

The last statement explains why the stars do not seem to move by parallax when the earth moves in its orbit. The actual parallactic motion was only detected by Bessel in 1837. The great size of Aristarchus's firmament moves the gods to a distance that removes all danger to humanity from them. Copernicus's reprise of Aristarchus in the 16th century had the same effect, which really caused the violent objection to the heliocentric view.


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Composed by J. B. Calvert
Last revised 1 July 1999