Aristarchus of Samos
Aristarchus of Samos was born in approximately 310 BC on the Greek island of Samos. He likely moved to Alexandria where he studied under Strato of Lampsacus. Strato later became the head of the Peripatetic school in Greece. This educational background placed Aristarchus within a tradition of rigorous philosophical inquiry. Ptolemy records that Aristarchus observed the summer solstice of 280 BC. Vitruvius writes that Aristarchus built two different sundials for practical observation. One was a flat disc and the other was hemispherical.
Archimedes describes a lost work by Aristarchus in his book The Sand Reckoner. This text advanced the heliocentric model as an alternative hypothesis to geocentrism. Aristarchus proposed that fixed stars were extremely distant from Earth. Ancient cosmology had placed all stars on a single celestial sphere. Aristarchus reconciled this issue by postulating that stars were other suns very far away. Their distance made parallax unobservable throughout Earth's motion. This implied a universe much larger than had been believed at the time.
Aristarchus claimed that at half moon the angle between the Sun and Moon was 87 degrees. Using correct geometry with this insufficiently accurate datum he concluded the Sun was between 18 and 20 times farther away than the Moon. He pointed out that the Moon and Sun have nearly equal apparent angular sizes. Therefore their diameters must be in proportion to their distances from Earth. During a lunar eclipse he measured the time it took for Earth's shadow to fully encompass the Moon. From there he determined the shadow cone width was twice the diameter of the Moon at full non-central eclipse. These calculations led him to estimate the Sun was approximately six times wider than Earth's diameter.
It is a common misconception that the heliocentric view was considered sacrilegious by contemporaries of Aristarchus. Lucio Russo traces this error to Gilles Ménage's printing of a passage from Plutarch's On the Apparent Face in the Orb of the Moon. In the manuscript Aristarchus says Cleanthes should be charged with impiety. Ménage transposed an accusative and nominative so it appeared Aristarchus was impious instead. The resulting misconception of an isolated and persecuted Aristarchus is still promulgated today. Seleucus of Seleucia maintained heliocentrism as a definite opinion a century after Aristarchus but no record of his demonstration exists.
Nicolaus Copernicus knew that Aristarchus had a moving Earth theory though unlikely awareness existed regarding its specific heliocentric nature. The heliocentric theory was revived by Copernicus centuries later. Johannes Kepler described planetary motions with greater accuracy using three laws. Isaac Newton later gave a theoretical explanation based on laws of gravitational attraction and dynamics. Pliny the Elder wondered whether errors in predictions about heavens could be attributed to displacement of Earth from its central position. Plato Aristotle and Ptolemy preferred the geocentric model believed throughout the Middle Ages.
The lunar crater Aristarchus bears the name of this ancient astronomer. A minor planet designated 3999 Aristarchus also honors him. The telescope named Aristarchos carries his legacy forward into modern space exploration. These tributes recognize his early insights despite the lack of surviving original texts. His work influenced Eratosthenes who calculated Earth's circumference and distance to the Sun. Hipparchus measured radii of the Sun and Moon as well as their distances from Earth. Posidonius calculated the circumference of the Earth following similar geometric traditions.
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Common questions
When and where was Aristarchus of Samos born?
Aristarchus of Samos was born in approximately 310 BC on the Greek island of Samos. He later moved to Alexandria to study under Strato of Lampsacus.
What did Aristarchus of Samos propose about the heliocentric model?
Aristarchus of Samos advanced the heliocentric model as an alternative hypothesis to geocentrism in his lost work The Sand Reckoner. He proposed that fixed stars were extremely distant from Earth and functioned as other suns very far away.
How did Aristarchus of Samos calculate the size of the Sun relative to Earth?
Aristarchus of Samos estimated the Sun was approximately six times wider than Earth's diameter using measurements taken during a lunar eclipse. He determined the shadow cone width was twice the diameter of the Moon at full non-central eclipse to derive this ratio.
Was Aristarchus of Samos considered sacrilegious by his contemporaries?
It is a common misconception that the heliocentric view was considered sacrilegious by contemporaries of Aristarchus of Samos. Lucio Russo traces this error to Gilles Ménage's printing of a passage from Plutarch's On the Apparent Face in the Orb of the Moon where Aristarchus said Cleanthes should be charged with impiety.
Who revived the heliocentric theory after Aristarchus of Samos died?
The heliocentric theory was revived by Nicolaus Copernicus centuries later though he likely lacked awareness regarding its specific heliocentric nature. Johannes Kepler described planetary motions with greater accuracy using three laws while Isaac Newton later gave a theoretical explanation based on laws of gravitational attraction and dynamics.