Lunar Crater

Aristarchus’s Model of the Universe

The lunar crater you see here is Aristarchus, and we’re not going to be be able to get any closer than that to an accurate portrait of the eponymous Ancient Greek astronomer because most of his writings — as well as any contemporary sculpture or paintings of the man — are lost to the sands of time.

In fact, the mathematician Archimidedes preserves Aristarchus’s most important discoveries in a work called _The Sand Reckoner_. Here’s a quote:

“. . . The ‘universe’ is the name given by most astronomers to the sphere the centre of which is the centre of the earth . . . . But Aristarchus has brought out a book . . . Wherein it appears . . . . 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 on the circumference of a circle, the sun lying in the middle of the orbit . .
“.

This, friends, was way back before 280 BCE, about when Aristarchus died — close to 1800 years before Copernicus advanced his heliocentric model of the universe. Besides positing that the earth and planets orbit the sun, he also reasoned that the stars are much further away than anyone had thought and therefore that the universe was fantastically bigger than any previous writers had speculated. (P.S. how he deduced this is interesting — he looked at the stars’ procession across the night sky and observed that they didn’t change position relative to each other — aka star parallax. If the earth orbits the sun but the other stars don’t shuffle around from your POV, then the distance between the stars has got to be really, really big.).

Aristarchus was right, of course. But Aristotle, Ptolemy, et al turned out to be louder voices, and so the heliocentric model was doomed to obscurity for the better part of two millennia. Not to throw shade on Ptolemy and the Greek astronomers — thinking that the sun goes around the earth really made sense from an observational perspective — it was absolutely possible to have mathematical predictability about the positions of the stars and planets using a (admittedly complex) geocentric model of the universe.

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