Britannica Sources used in this answer

Which locations did Hipparchus compare during a solar eclipse to calculate lunar parallax?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Engraving of six astronomers, with Hipparchus seated at center and, from left to right, Galileo, Johannes Hevelius, Tycho Brahe, Nicolaus Copernicus, and Ptolemy standing, each holding scientific instruments. — Hipparchus “Six astronomers,” the frontispiece of *Astronomica Institutio* (1692) by Jan Luyts, engraving after drawing by Gerard Hoet. Hipparchus is seated at center with from left to right: Galileo, Johannes Hevelius, Tycho Brahe, Nicolaus Copernicus, and Ptolemy.

To calculate the lunar parallax, Hipparchus compared observations of a solar eclipse that was total near the Hellespont (now known as the Dardanelles) and only partial at Alexandria.1

He attributed the difference in the appearance of the eclipse between these two locations to the Moon's observable parallax, which allowed him to estimate the Moon's mean distance from Earth.1