Where did Hipparchus conduct most of his astronomical observations?

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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.

Hipparchus spent the majority of his adult life conducting his program of astronomical observation and research on the island of Rhodes.1

While he compiled weather records in Bithynia as a young man, Ptolemy later cited numerous observations made by Hipparchus on Rhodes between 147 and 127 BCE. Additionally, Hipparchus maintained communication with other observers, including those in Alexandria and likely Babylon, to assist in his scientific work.1