Who first proposed the heliocentric model of the solar system?

Who first proposed the heliocentric model of the solar system? Aristarchus of Samos is the first known person credited with doing so.

Around the 3rd century BCE, this Greek astronomer suggested that Earth rotates on its axis and travels around the Sun, rather than remaining motionless at the center of the cosmos. His original work on the model has not survived, but Archimedes described Aristarchus’s ideas in The Sand-Reckoner, preserving the key claim.

Aristarchus’s proposal was far ahead of its time. Most ancient astronomers later favored a geocentric system, especially the detailed Earth-centered model developed by Claudius Ptolemy. Because Aristarchus’s model lacked the observational evidence and mathematical framework needed to persuade other scholars, it was largely set aside for many centuries.

A common mix-up is to name Nicolaus Copernicus, who revived and developed heliocentrism in the 16th century. Copernicus was crucial to the scientific revolution, but Aristarchus proposed the Sun-centered arrangement roughly 1,800 years earlier. Aristarchus also estimated the relative sizes and distances of the Sun and Moon using geometry, though his measurements were limited by ancient instruments.