![]() ![]() Over the winter break, on a trip to Florida from Pennsylvania, the author had the opportunity to repeat these measurements. ![]() Anyone with access to Route 95 and a tape measure can repeat Eratosthenes' measurement, and can even use a baseline that is longer than his. Route 95 runs all the way from Maine to Florida. In Eratosthenes' experiment, A would correspond to the well at Aswan, on the day of the summer equinox, and Alexandria would be located somewhere between A and B. (This assertion can be tested by observing a beam of light from the sun which passes through a 1mm hole in a large piece of cardboard.) In the figure, a vertical stick at point A would cast no shadow, a stick at B would cast a "moderate" shadow, and a stick at C would cast a very long shadow. ![]() His results and modern results agree within about 10%.īecause the sun is assumed to be very far away, we believe that the light rays which reach us from the sun are all going in the same direction they are parallel. ![]() He concluded that the circumference of the earth was about 50 times greater than the distance from Alexandria to Aswan. The geometry of the situation is sketched at the right. The length of that shadow was not zero because the sun was not directly overhead in Alexandria.Įratosthenes analyzed the observations with the assumption that the earth is a sphere and the sun is very far away. On the same day, Eratosthenes measured the shadow of the a stick at noon in Alexandria. On that day, the sun at noon was directly overhead at Aswan. As recounted by Alder (Ken Alder, The Measure of All Things, The Free Press (Simon&Shuster) 2002, p91), Eratosthenes knew of a deep well near Aswan on the Nile where the sun shined all the way to the bottom at noon on the day of the summer solstice. Thanks to Gregor Shapiro for corrections to this article.)Ĭredit for the first estimate of the Earth's radius goes to Eratosthenes, in Alexandria, around 240 B.C.E. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |