კარლ სეიგანი: გინორთი გინოჯინეფს შქას

* [https://www.lindahall.org/carl-sagan/ Scientist of the Day-Carl Sagan] at Linda Hall Library

* [https://www.youtube.com/watch?v=8hZl3arO7SY Carl Sagan demonstrates how Eratosthenes determined that the Earth was round and the approximate circumference of the earth.]

 

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