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 was the first known astronomer to make a recorded observation of the planet Mercury, in 265 BC.
The Timocharis crater on the Moon is named in his honor.
External links
Windows to the Universe: Discover Mercury (http://www.windows.ucar.edu/tour/link=/mercury/News_and_Discovery/news_disc_overview.html&edu=high)
The Astronomer Hipparchus of Rhodes (http://www.mlahanas.de/Greeks/Hipparchus.htm) - mentions Timocharis' contribution
It was total in the region of the Hellespont (and in fact in his birth place Nicaea); at the time the Romans were preparing for war with Antiochus III in the area, and the eclipse is mentioned by Livy in his Ab Urbe Condita VIII.2.
Alexandria is at about 31° North, and the region of the Hellespont at about 41° North; authors like Strabo and Ptolemy had fairly decent values for these geographical positions, and presumably Hipparchus knew them too.
Ptolemy compared his catalogue with those of Aristyllus, Timocharis, Hipparchus and the observations of Agrippa and Menelaus of Alexandria from the early 1st century and he finally confirmed Hipparchus' empirical fact that poles of the celestial equator in one Platonic year (approximately 25,777 sidereal years) encircle the ecliptical pole.
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