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Question regarding Sun's Rays

  1. Sep 13, 2014 #1
    Well I just took a introductory course in physics at Udacity.com a while back . In that , I learned about Archimedes attempt at calculating the radius of Earth . According to that , at a place near Syracuse , Greek , the sun rays fall at 90 degrees on the summer solstice . Just wanted if you guys could confirm that fact , because that is the basis for an idea of mine .
  2. jcsd
  3. Sep 13, 2014 #2


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    The tilt of the Earth is only 23.5 degrees. At 43 degrees north in latitude, rays from the Sun never fall on Syracuse at 90 degrees.
  4. Sep 13, 2014 #3


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  5. Sep 13, 2014 #4
    Yeah jtbell , you are 100 % correct , sorry for my "weak" memory though I am only 14 :) . I was just about to correct that :
    "A Greek named Erasthothanes noticed this phenomenon in 250 BCE at Aswan, Egypt. He’d previously measured the length of his small solstice shadow in Alexandria, and he used those data points—the length of his shadow at Alexandria, the length (0) of his shadow at Aswan, and the distance between the two—to calculate both the diameter of the Earth and the tilt of the planet’s axis."
  6. Sep 19, 2014 #5
    Watch the original Cosmos series and Sagan talks about that experiment by Erasthothanes. I *think* it was in the first episode, but I could be mistaken.
  7. Sep 19, 2014 #6
    Yeah, you need to realize that some of us were there at the time. :)
  8. Sep 19, 2014 #7


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    By the way, many of us learned in elementary school, and I am sure it is still taught, that Christopher Columbus, unlike everyone else at the time, believed that the earth was round, not flat, and that you could reach the orient by traveling west.

    In fact, Eratosthenes, over a thousand years earlier, not only knew that the earth was round but had calculated its diameter! Where Columbus differed from most people was that he was a member of a small group of people who believed that Eratosthenes' result was too large- on purely "stylistic" reasons. They just didn't believe that the earth was almost all land (Europe, Asia, Africa) on one side and empty ocean on the other! Of course, they, and Columbus, were wrong.
  9. Sep 19, 2014 #8


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    It is worth while remembering, when considering how 'wrong' they were in the fairly distant past, that there are still many people who believe that the Earth is only four thousand years old DESPITE the vast amount of contrary evidence.
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