The ancient Greeks knew this shit. Which always impresses me -- screw arguing over geocentrism versus heliocentrism, I like hearing how the Greeks figured out the size of the Earth-Sun-Moon system*, modeling orbits, and measuring that the Earth wobbles like a top.

But it ruins my joke that I'm an Ophiuchus, the sign that thinks astrology is bullshit.

* Granted, with errors given they were working naked eye, but Aristarchus of Samos knew the Sun was bigger than the Earth.