Astronomy 100
Section 2, Fall 2008
Homework H
Answers
1. We know the temperatures of the planets, Sun, and stars from
application of
a) The Wien and Stefan-Boltzmann Laws
2. We know the chemical composition of the Sun from its
a) spectrum (specifically from its absorption lines)
3. The surface of the Sun is
a) an opaque hydrogen-helium gas
4. The temperature of the Sun's corona is about
c) 2 million K
5. The third most abundant element in the Sun is
c) oxygen
6. If you took all the hydrogen and helium away from the Sun, the
resulting
mixture would have a chemical composition rather similar to
a) the Earth's crust
7. The Sun rotates
a) every 25 days at the equator in the direction of the
planetary
orbits
8. Sunspots are produced by
c) magnetic fields that block convection (causing a spot in
the photosphere to cool)
9. Absorption lines in the solar spectrum are produced by
a) the electrons associated with atoms and ions
10. The solar corona is heated by
d) magnetism
11. What event on the Sun causes aurorae on Earth?
a) coronal mass ejections
12. The Sun's magnetic field is produced by its
d) rotation and convection
13. The lifetime of a particular sunspot is closest to
b) a week
14. The length of the solar sunspot cycle (ignoring the direction
of magnetic
fields) is
c) 11 years
15. The solar wind
b) is a flow of particles from the Sun
16. When the sunspots (magnetic activity) disappeared around the
year 1700,
e) North America and Europe became colder
17. Where does solar hydrogen fusion take place?
e) the deep core (where the Sun is sufficiently hot and
dense)
18. In the center of the Sun, two protons fuse directly to
a) deuterium
19. About how much hydrogen-burning time does the Sun have left to
it, in
billions of years?
b) 5 (It had 10 billion years to start with, and it is now
about 5 billion years old.)
20. What particles immediately escape the solar core following
fusion?
a) neutrinos
21. What makes the Sun hot in its center (hot enough to run
fusion)?
e) gravitational compression
22. Why does the Sun not explode as a hydrogen bomb?
c) The first reaction of the proton-proton chain is too
slow
23. A 2nd magnitude star is how many times brighter than a 12th
magnitude
star?
d) 10,000 (A ten magnitude difference is two sets of five
magnitudes, so a 2nd magnitude star is 100X100 = 10,000 times
brighter than a 12th magnitude star)
24. The absolute magnitude of a star is what the apparent magnitude
would be
at how many parsecs?
b) 10
25. Which magnitude would appear brightest to the naked eye?
a) -1