Timocharis of Alexandria

Timocharis of Alexandria (circa 320 BC - 260 BC) was a Greek astronomer and philosopher. Likely born in Alexandria, he was a contemporary of Euclid.

In approximately 300 BC, with the help of Aristillus, he created the first star catalogue. Over 150 years later, Hipparchus would compare his own star catalogue to Timocharis' and discover that the longitude of the stars had changed over time, which led him to determine the first value of the precession of the equinoxes.

Timocharis, the astronomer, made some of his observations at Alexandria in the last reign, and continued them through half of this reign. He began a catalogue of the fixed stars, with their latitudes and their longitudes measured from the equinoctial point; by the help of which Hipparchus, one hundred and fifty years afterwards, made the great discovery that the equinoctial point had moved. He has left an observation of the place of Venus, on the seventeenth day of the month of Mesore, in the thirteenth year of this reign, which by the modern tables of the planets is known to have been on the eighth day of October, B.C. 272; from which we learn that the first year of Philadelphus ended in October, B.C. 284, and the first year of Ptolemy Soter ended in October, B.C. 322; thus fixing the chronology of these reigns with a certainty which leaves nothing to be wished for. Aris-tillus also made some observations of the same kind at Alexandria S. Rappoport, History of Egypt

Timocharis was the first known astronomer to make a recorded observation of the planet Mercury, in 265 BC.

The Astronomer Hipparchus of Rhodes - mentions Timocharis' contribution

The Timocharis crater on the Moon is named in his honor.


Windows to the Universe: Discover Mercury

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