Describe how Eratosthenes first measured the size of Earth over 2000 years ago
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Eratosthenes used measurements of the angle of the Sun in the sky at noon on the summer solstice in two places in Egypt. It was directly overhead in Syene and cast no shadows. In Alexandria, however, there was a slight shadow, indicating that the Sun was 7 degrees away from overhead. Eratosthenes concluded that Alexandria lies at a latitude 7 degrees north of Syene. The circumference of Earth is then the distance between Syene and Alexandria divided by the fraction of the circle (7/
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A) Mercury B) Venus C) Earth D) Mars E) all of the above
Astronomers knew for some time that the rings of Saturn are thin, because they could see stars through the rings.
Answer the following statement true (T) or false (F)
The maximum number of electrons allowed in the n = 1 shell of sodium is
A. 2. B. 6. C. 8. D. 4. E. unlimited.
What do we mean by the critical density of the universe?
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