In addition to that, early measurements were made by trying to compute the angle of the Sun to the horizon when the Moon was exactly at quarter. The angles involved are very small (or very close to 90 degrees) making the results very sensitive to errors. The wikipedia article gives a good overview of the ideas:
http://en.wikipedia.org/wiki/Astronomical_unit#History
http://www.solipsys.co.uk/HowHighTheMoon.pdf
In addition to that, early measurements were made by trying to compute the angle of the Sun to the horizon when the Moon was exactly at quarter. The angles involved are very small (or very close to 90 degrees) making the results very sensitive to errors. The wikipedia article gives a good overview of the ideas: http://en.wikipedia.org/wiki/Astronomical_unit#History
This article also covers the basics: http://galileoandeinstein.physics.virginia.edu/lectures/gkas...
But you probably knew all that.