# 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