On the Sizes and Distances of the Sun and Moon

Aristarchus of Samos, a Greek astronomer from around 310-230 BCE, proposed a heliocentric model of the solar system, suggesting Earth rotates on its axis and revolves around the Sun. His treatise, On the Sizes and Distances of the Sun and Moon, is the earliest known geometric approach to this problem.1

Aristarchus used observations, including lunar eclipses and the angular diameter of celestial bodies, to estimate the relative distances and sizes of the Sun and Moon. He concluded the Sun was significantly farther away than the Moon, though his numerical estimates were not entirely accurate due to limitations in measurement capabilities at the time. His work, however, laid foundational geometric methods for later astronomers like Hipparchus and Ptolemy.12