Astronomy 100

Section 2, Fall 2008

Homework C

Answers

1. Most proper star names are
d) Arabic

2. The modern constellations were invented
d) between AD 1600 and 1800

3. Which would ordinarily be the name of the brightest star in a constellation?
b) Alpha

4. The Milky Way is made of
a) stars in the disk of our Galaxy

5. At what phase is the Moon 270 degrees to the east of the Sun as seen from Earth?
d) third quarter

6. Earthlight on the Moon is best seen at which of the phases given below?
a) waning crescent (when, as seen from the Moon, the Earth is close to full)

7. On the average, the full Moon rises at
d) 6 PM (since it is then opposite to the Sun)

8. When will you see a thin crescent Moon at midnight from Urbana?
e) never (since the thin crescent must be angularly close to the Sun)

9. As the Moon moves through the stars it roughly follows the
a) ecliptic

10. The Moon's phases are caused by
d) our seeing different portions of the daylight side of the Moon as the Moon orbits the Earth

11. At what phase is the Moon's far side in full daylight?
a) new Moon (since the near side points to Earth and the far side to the Sun)

12. If the Moon is at its new phase, someone on the Moon would "see" the Earth at
c) full

13. At what phase is it possible to see an eclipse of the Moon?
a) full (since the Moon must be opposite to the Sun for it to go through the Earth's shadow)

14. You do not see a total eclipse of the Moon every month because
d) the Moon's orbit is tilted relative to the ecliptic

15. The brightness of the totally eclipsed Moon is controlled largely by
a) volcanic action on Earth (The eclipsed Moon is visible because of light scattered by the Earth's atmosphere into the shadow, and volcanic activity decreases atmospheric transparency.)

16. Very few people see any given total eclipse of the Sun because
a) the Moon's shadow spot is so small

17. Total eclipses of the Sun take place
d) at new Moon near perigee (The Moon must be between the Earth and Sun and must be close to Earth in its orbit for the shadow to reach us.)

18. When Jupiter is in opposition to the Sun, it will rise about
d) 6 PM (at sunset)

19. When Saturn is in retrograde, it will be moving mostly in what direction relative to the background stars?
d) west

20. Which pair of planets can never be seen from Urbana at midnight?
e) Venus and Mercury

21. Which planet can be seen in a crescent phase from Earth?
a) Mercury

22. Which planet listed below has the longest sidereal orbital period?
c) Uranus (The farther away the planet from the Sun, the longer the sidereal period.)

23. The orbit of Mars is an ellipse with the Sun at
a) one focus

24. Who used Tycho's positions of planets to find the laws that describe planetary motion?
b) Kepler

25. What did Copernicus put at the center of the Solar System?
b) the Sun