Aside from being one of the most notable philosophers in history, Thales of Miletus endeavored in the field of astronomy. So much so that he is said to have predicted a solar eclipse in the year 585BC.
This change from daylight to darkness had been foretold to the Ionians by Thales of Miletus.. – Herodotus (iep)
Scholars are uncertain as to what method Thales used in predicting the solar eclipse, however, it took a couple centuries to repeat this accomplishment.
Supposedly Thales discovered an 18 year cycle of Sun and Moon movements known as the Saros cycle, which is what later ancient astronomers used to predict solar eclipses.