Homework 1 Answers

1. Chapter 2, 5-8:
   • 5 - This makes sense, as there are many southern constellations that can be seen from South America but not from North America
   • 6 - This doesn't make sense. The Big Dipper isn't near the ecliptic, so none of the planets should ever be seen there.
   • 7 - This doesn't make sense. Retrograde motion takes weeks to observe. In one night, you couldn't see the motion.
   • 8 - This doesn't make sense. The daily motions of the stars is caused by Earth's spin. Since Earth will always spin in the same direction, all the stars will always rise in the Eart.
2. Chapter 2, Problem 11:
   1. The Earth would be in its new phase, because it lies between us and the Sun.
   2. No, the Earth would never rise or set. Because the Moon always keeps the same face to the Earth, the Earth would always be up.
   3. During a lunar eclipse, we'd see the Earth pass in front of the Sun. (John notes: Since the Earth's angular size is much larger than the Sun's, as seen from the Moon, it wouldn't be nearly as cool as a solar eclipse on Earth.) During a solar eclipse (for Earth), we would see the shadow of the Moon move across the Earth's surface.
3. Chapter 2, Problem 12: No, we could no longer have a total solar eclipse. Since the Moon is twice as far away, it is twice as small (in angular size), so it can no longer cover the Sun. Annular eclipses would still happen, although they'd be less cool, since the Moon could still pass in front of the Sun. (Just not cover all of it at once.) And lunar eclipses would continue, since Earth's shadow extends well past that into space. (Note: if anyone thought Earth's shadow would disappear by this point, give them full credit. The math needed to show what the shadow does isn't very difficult —it's just geometry — but I don't expect anyone to actually work itb out.)
4. Chapter 3, Problems 2 and 5:
   • 2 - Doesn't make sense. Christmas is Decemeber 25th of every year. If it were set by the lunar calendar, it would vary in date, like Easter does.
   • 5 - Students could go either way on this one. Makes sense: Theories are just "best guesses" and could easily be wrong. Doesn't make sense: Theories are more than guesses because they are tested against data. How you deciede is really based on how you define "guess."