Aristotle was one of the few ancient Greek philosophers whose writings survived to the current day. His book De Caelo (On the Heavens), written around 330 B.C. described the spherical Earth idea, which had been proposed several centuries earlier, and gave reasons for believing it to be true, including:

  • Travelers going south notice that southern constellations rise higher in the sky the further they go.
  • Earth’s shadow on the Moon during a partial lunar eclipse is always curved.