Astronomy 122&, Fall 2009

Homework D: Due Monday, September 28

Part I: Multiple choice. On your scantron fill out your NAME, STUDENT NUMBER, and NETWORK ID both in writing and in the bubbles. In addition, fill out "FORM D."

1. The Sun is how many times more massive than Jupiter?
a) 10 b) 100 c) 1000 d) 10,000 e) 100,000

2. The Sun is made mostly of
a) gaseous hydrogen and helium
b) water
c) oxygen, nitrogen, and carbon
d) light metals like calcium and sodium
e) liquid molecular hydrogen

3. The diameter of the Sun is about
a) 860,000 miles
b) 1.5 million km
c) 109 Earth diameters
d) 0.01 AU
e) all of the above

4. The temperature of the solar photosphere (the optically visible "surface") is about
a) 1000 K b) 6000 K c) 10,000 K d) 20,000 K e) 60,000 K

5. What causes the solar granulation?
a) radiation
b) convection
c) magnetic fields
d) electric currents
e) rotation

6. We know the chemical composition of the Sun from its
a) spectrum
b) rotation
c) temperature
d) magnetism
e) convection

7. The surface of the Sun is
a) an opaque hydrogen-helium gas
b) solid hydrogen
c) liquid molecular hydrogen
d) liquid metallic hydrogen
e) made of gaseous iron and nickel

8. The temperature of the Sun's corona is about
a) 3500 K
b) 5800 K
c) 2 million K
d) 20 million K
e) 200 million K

9. The third most abundant element in the Sun is
a) hydrogen
b) iron
c) oxygen
d) helium
e) lithium

10. 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
b) a comet
c) Jupiter
d) Saturn
e) Ganymede

11. The Sun rotates
a) every 25 days at the equator in the direction of the planetary orbits
b) once a week in the direction of the planetary orbits
c) every 25 days opposite to the direction of the planetary orbits
d) once a day opposite to the direction of the planetary orbits
e) not at all

12. Sunspots are produced by
a) coronal mass ejections
b) nuclear explosions
c) magnetic fields that block convection
d) the solar wind
e) hurricane like low-pressure areas

13. The solar corona is heated by
a) radiation
b) convection
c) conduction
d) magnetism
e) cometary impacts

14. What event on the Sun causes aurorae on Earth?
a) coronal mass ejections
b) thermonuclear explosions
c) sudden sunspot disappearances
d) irregular solar rotation
e) radioactivity

15. The Sun's magnetic field is produced by its
a) corona
b) wind
c) nuclear reactions
d) rotation and convection
e) sunspots

16. The lifetime of a particular sunspot is closest to
a) a minute b) a week c) a year d) 11 years e) 22 years

17. The length of the solar sunspot cycle (ignoring the direction of magnetic fields) is
a) a week b) a year c) 11 years d) 22 years e) 33 years

18. The solar wind
a) is produced by comet tails and flows into the Sun
b) is a flow of particles from the Sun
c) blows into the Sun from the Van Allen radiation belts
d) is a flow of neutrinos from the solar center
e) is the thin gas in interplanetary space falling into the Sun.

19. When the sunspots (magnetic activity) disappeared around the year 1700,
a) the number of northern lights displays increased
b) nothing else happened
c) the Earth's magnetic field disappeared
d) there were no eclipses of the Moon
e) North America and Europe became colder

20. Where does solar hydrogen fusion take place?
a) the photosphere
b) the solar wind
c) the corona
d) sunspots
e) the deep core

21. In the center of the Sun, two protons fuse directly to
a) deuterium
b) helium-3
c) helium-4
d) nothing
e) gamma rays

22. About how much hydrogen-burning time does the Sun have left to it, in billions of years?
a) 1 b) 5 c) 10 d) 50 e) 100

23. What particles immediately escape the solar core following fusion?
a) neutrinos
b) protons
c) gamma ray photons
d) neutrons
e) positrons

24. What makes the Sun hot in its center (hot enough to run fusion)?
a) the strong force
b) gamma rays
c) tides raised by the planets
d) rapid interior rotation
e) gravitational compression

25. Why does the Sun not explode as a hydrogen bomb?
a) It will
b) The last reaction of the proton-proton chain is too fast
c) The first reaction of the proton-proton chain is too slow
d) There is not enough hydrogen left to run the p-p chain
e) We don't know

Part II. Show all your work.

1. How much mass (in kilograms) must be lost by the Sun each second to produce its observed power output of 4 X 10**26 watts? Show your calculations. (Remember that E(energy)=M(mass)c**2.)

2. If the Sun is made mostly of hydrogen, why are the hydrogen absorption lines not the strongest lines in the solar spectrum?

3. How might the Earth be affected if the Sun stopped rotating?

Note: Express your answer to question 1 in kilograms. A joule is the unit of energy; one joule/second = 1 watt. The speed of light must be expressed in meters/second to obtain energy in joules.