(Jon of the Clue Crew points to an astronomical diagram on the monitor.)  In the 200s B.C. Eratosthenes calculated Earth's girth using the difference in the angle of the Sun's rays between Aswan & this Egyptian city
He measured the Sun's angle of elevation at noon on the same 
day in... [DOC] [TLE] Download [PAR] Aug 19, 2001 ... Meteor and Aurora Detection Using Modern Video Technologies ... 14 Exploring 
the Astronomy of Ancient Egypt .... between the Earth and the Sun varies.