TITLE: How can I conclude that I live in a solar system?
QUESTION [15 upvotes]: Well, this is an awkward question and I don't know if it is mathematical enough for MO (I'm sorry if not) but I'll try it: What observations in the coordinate system centered in my fixed position on earth are necessary to conclude that the earth (and the planets) move (approximately) in ellipses around the sun and that earth is rotating around itself?

REPLY [2 votes]: An interesting (and very old) argument in favour of heliocentrism is based on estimates of the relative sizes of the Earth and Sun.  
Actually,  Aristarchus of Samos estimated that the Sun is six to seven times wider than the Earth (and therefore over 200 times more voluminous). These calculations arguably led him to conclude that it made more sense for the Earth to be moving than for the huge Sun to be moving around it.