How would we measure the size of the moon? the sun? other heavenly bodies? How would we begin? We might guess that some measuring of angles, followed by a calculation involving trigonometry would make a good start.
Hipparchus of Rhodes, who lived around 190 BC – 120 BC, was a Greek mathematician, the greatest astronomer of antiquity, and the father of trigonometry. He was able to find not only the radius of the moon, but also the distance between the earth and the moon, and the earth and the sun.
http://en.wikipedia.org/wiki/Hipparchus
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