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c. 270 BCEReputable source · 2 sourcesWell documented

Aristarchus Proposes a Sun-Centered Universe, 1,700 Years Too Early

A lone Greek astronomer puts the Sun in the middle and is ignored for nearly two millennia

On the timeline · around c. 270 BCE · Ancient AstronomyAncient AstronomyMedieval and Islamic AstronomyAristarchus Proposes a Sun-Centered Universe, 1,700 Years Too Early1,000 BCE750 BCE500 BCE250 BCE1 CE250 CE500 CE

Quick facts

Astronomer
Aristarchus of Samos, c. 310-230 BCE
Proposal
Earth revolves around a central Sun
Surviving work
On the Sizes and Distances of the Sun and Moon
Years before geocentric model was overturned
c. 1,700

What happened

Aristarchus of Samos, working in the third century BCE, proposed that the earth revolves about the sun on the circumference of a circle, with the sun lying in the middle of the orbit, making him the first known Greek astronomer to argue for a heliocentric universe rather than an Earth-centered one. In his one surviving work, On the Sizes and Distances of the Sun and Moon, Aristarchus used geometric reasoning based on the angle between the Sun and Moon at half-moon to estimate that the sun was between 18 to 20 times as far away as the moon, an estimate far too small by modern measurement but methodologically sound in its approach. His heliocentric idea itself does not survive in his own writing and is known only through references by later authors, including Archimedes.

Why it matters

Aristarchus anticipated Copernicus's heliocentric model by roughly 1,800 years, but his idea found no lasting support in antiquity: it was noted by contemporaries and then set aside as implausible, and the geocentric model held the field instead for the next 1,700 years, reaching its most developed form under Ptolemy. His case shows that having the right idea was not enough without a mathematical model that could out-predict the rival system, something Copernicus himself would still struggle to achieve when he revived the idea in the sixteenth century.

How we know

Aristarchus's heliocentric proposal is known only second-hand, through references in the surviving works of other ancient authors including Archimedes' The Sand Reckoner, since none of his own writing on the theory has survived; his distance-estimate treatise, On the Sizes and Distances of the Sun and Moon, does survive intact and lets historians verify his geometric method directly.

Sources

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Part of a timelineHistory of Astronomy26 events · Priests reading omens in the stars, monks charting eclipses from a minaret, and a telescope in orbit reading the light of the first galaxiesView all →
Aristarchus Proposes a Sun-Centered Universe, 1,700 Years Too Early · History of Astronomy · SourcedStory