Following up on these posts:
Today I read Beyond the Book (and What the Greeks Knew About the Earth) in which Professor Matt Strassler explains one of the ways the ancient Greeks knew that the Earth was round and how one of them (Eratosthenes of Cyrene} was able to make a reasonably accurate calculation of its circumference. This calculation assumes that the Sun is much further away from the Earth than the Moon, and hence much bigger, than the Earth of the Moon. Which is Bigger, the Sun or the Earth? Check it Yourself! explains how the Greeks knew this.
From Hilbert Space to Dilbert Space, and beyond 