Ancient calculations and observations

1. Nov 26, 2007

scerab

Would any one help me understand how did the ancient Greeks managed to calculate the earth’s circumference using knowledge of the angle of elevation of the Sun. I wonder if they had any means of magnification such as lens. They did make some pretty accurate conclusions for the limited technology they used.
Another question: were the ancient Greeks the first to assume the earth was round rather then flat?

2. Nov 26, 2007

mathman

The basis tool that was used to estimate the earth's circumference was a stick of fixed length. The length of the shadow at noon was measured at two different locations (I don't remember the distance apart, but I believe it was over 100 miles) along a north-south line. From the shadow lengths, the angle of the sun at these locations could be calculated.

Last edited: Nov 27, 2007
3. Nov 26, 2007

Chris Hillman

The distance between those two locations was considered "known" in terms of stadia, and here things turn a bit murky, but I believe that messengers regularly ran between the two towns and their times formed a crude estimate of distance. Thus the Greeks were able to express the diameter of the Earth in terms of a familiar unit, the stadium.

4. Nov 26, 2007

Staff: Mentor

5. Nov 26, 2007