Owen,
The person who is credited with first measuring the circumference, and =
therefore the radius, of the earth is Eratosthenes, in Egypt, around 200 =
B.C. This is in most of the astronomy texts I am familiar with, though =
some are tending to leave it out in favor of more trendy things. =
Aristotle, c. 350 B.C., cited convincing evidence that the earth is round =
like a ball--curvature of the earth's shadow on the moon during a lunar =
eclipse, independent of where the moon is in the sky; ships disappearing =
bottom to top as they put out to sea, etc. But apparently Eratosthenes =
was the first to come up with a value. You can find the story in Carl =
Sagan's "Cosmos", on pp. 14 ff. =20
The observations involved the fact that at a rural location on the =
Tropic of Cancer, Syene, vertical sticks cast no shadows, and sun light =
reflected from the bottom of wells at noon on June 21. At the same time, =
vertical sticks cast a shadow found to be about 7 degrees in the northern =
city of Alexandria. Knowing the distance between the two cities and a =
little geometry yields the circumference of the earth.
BTW: A few years ago a colleague and I published a way the size of the =
earth was measured from observing two sunsets in an airplane. This was =
written up in TPT, vol. 25, p. 477 (1987).=20
Hope this helps.
Rondo N. Jeffery
Physics Department
Weber State University
Ogden, UT 84408-2508
<KUGELGEN@aol.com> 10/07 8:33 AM >>>
Hello all,
Can anyone out there remember who first measured the radius of the earth?
An Egyptian, a Greek? What was his/her name?
(I'm working with a teacher in another city (due north), measuring solar
angles
and calculating the Earth's radius)
Responses can be sent privately to kugelgen@aol.com.
If the answer does not appear on the list, I'll post it for those who =
might be
interested.