Full Idea
Clearly the earth is round and not of great size, because when we move north or south we find that very different stars are visible.
Gist of Idea
The earth must be round and of limited size, because moving north or south makes different stars visible
Source
Aristotle (On the Heavens [c.336 BCE], 297b30)
Book Reference
Aristotle: 'On the Heavens I and II', ed/tr. Leggatt,Stuart [Aris and Phillips 1995], p.167