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Physics 20A: Introduction to Astronomy
Homework assignment #2
Due October 13
1. Textbook, p. 88, #3.
Answer:
If the moon were moved to twice its current distance from Earth, then its diameter would have to
be doubled in order for total solar eclipses to occur.
2. Textbook, p. 88, #12.
Answer:
In one hour, the sky rotates by 1/24 of a complete circle, or 1/24 of 360 degrees. 360
/
24 = 15, so
the sky rotates 15 degrees per hour.
3. Is it possible for an observer on Earth to see a total lunar eclipse at noon? Explain why or why not.
Answer:
For an observer in Irvine, this would never be possible. At noon the Sun is at its higest elevation
above the horizon for the day, and during a lunar eclipse the Sun and Moon have to be on opposite sides of
the Earth. So at noon in Irvine, if a total solar eclipse were occurring, it would only be visible for observers
on the opposite (nighttime) side of the Earth.
For an observer near the north or south pole, however, the answer is a bit more complicated. Think about
what might happen for an observer near the north pole in winter, when the Sun is below the horizon. If a
luar eclipse happened then, with the Moon above the horizon, all observers close to the North pole would
see it, and some of those observers would be in time zones where the local time is around noon while other
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This homework help was uploaded on 04/16/2008 for the course PHYS 20A taught by Professor Staff during the Winter '02 term at UC Irvine.
 Winter '02
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