AST 105 HW #5
Week of September 21st, 2015
Note: All Problems are from The Cosmic Perspective (7ed)
Chapter 14
Review Problems
1. Briefly describe how gravitational contraction generates energy. When was it important in the Sun’s
history? Explain.
2. What two forces are balanced in gravitational equilibrium? What does it mean for the Sun to be in energy
balance?
6. Why does nuclear fusion require high temperatures and pressures?
9. Why has the Sun gradually brightened with time?
13. What do we mean by solar activity? Describe some of features of solar activity, including sunspots, solar
prominences, solar flares, and coronal mass ejections.
17. What is the sunspot cycle? Why is it sometimes described as an 11-year cycle and sometimes a 22-year
cycle? Are there longer term changes in solar activity?
Test Your Understanding
Decide whether the statement makes sense (or is clearly true) or does not make sense (or is clearly false).
Explain clearly; not all of these have definitive answers, so your explanation is more important than your
chosen answer.
19. Before Einstein, gravitational contraction appeared to be a perfectly plausible mechanism for solar
energy generation.
20. A sudden temperature rise in the Sun’s core is nothing to worry about, because conditions in the core
will soon return to normal.
21. If fusion in the solar core ceased today, worldwide panic would break out tomorrow as the Sun began to
grow dimmer.
22. Astronomers have recently photographed magnetic fields churning deep beneath the solar photosphere.
23. I wear a lead vest to protect myself from solar neutrinos.
24. If there are few sunspots this year, we should expect many more in about 5 years.
25. News of a major solar flare today caused concern among professionals in the fields of communication
and electrical power generation.
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26. By observing solar neutrinos, we can learn about nuclear fusion deep in the Sun's core.
27. If the Sun’s magnetic field somehow disappeared, there would be no more sunspots on the Sun.
28. Scientists are currently building an infrared telescope designed to observe fusion reactions in the Sun’s
core.
Quick Quiz
Choose the best answer to each of the following. Explain your reasoning with one or more complete
sentences.
29. Which of these groups of particles has the greatest mass?
(a) a helium nucleus with two protons and two neutrons
(b) four electrons
(c) four individual protons
33. Why do sunspots appear darker than their surroundings?
(a) They are cooler than their surroundings.
(b) Thye block some of the sunlight from the photosphere.
(c) They do not emit any light.
38. Which of these things poses the greatest hazard to communication satellites?
(a) photons from the Sun
(b) solar magnetic fields
(c) particles from the Sun
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