Scholarly History of Ptolemy’s Star Catalog Index

The discussion surrounding Ptolemy’s star catalog is a fascinating one. While astronomers for hundreds of years took Ptolemy’s catalog as authoritative, Tycho Brahe noticed that the positions of the stars had a $\approx 1ยบ$ error in longitude. To explain this, Brahe hypothesized that this was due to Ptolemy stealing the data for the star catalog from Hipparchus and updating the longitudes with an incorrect constant of precession.

Astronomers have been debating this ever since.

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