Questions

Review Questions

Question 9.1

What is meant by the luminosity of the Sun?

Question 9.2

What is thermonuclear fusion? Why is this fusion fundamentally unlike the burning of a log in a fireplace?

Question 9.3

Why do thermonuclear reactions occur only in the Sun’s core, not in its outer regions?

Question 9.4

If thermonuclear fusion in the Sun were suddenly to stop, what would eventually happen to the overall radius of the Sun? Justify your answer using the ideas of hydrostatic equilibrium and thermal equilibrium.

Question 9.5

Give some everyday examples of conduction, convection, and radiative diffusion.

Question 9.6

What is a neutrino? Why is it useful to study neutrinos coming from the Sun? What do they tell us that cannot be learned from other avenues of research?

Question 9.7

Briefly describe the three layers that make up the Sun’s atmosphere. In what ways do they differ from each other?

Question 9.8

How do astronomers know when the next sunspot maximum and sunspot minimum will occur?

Question 9.9

Why do astronomers say that the solar cycle is 22 years long, even though the number of sunspots varies over an 11-year period? 10. Explain how the magnetic-dynamo model accounts for the solar cycle.

Question 9.10

Why should solar flares and coronal mass ejections be a concern for businesses that use telecommunication satellites?

Web Chat Questions

Question 9.1

Discuss the extent to which cultures around the world have worshiped the Sun as a deity throughout history. Why do you suppose there has been such widespread veneration?

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Question 9.2

In the movie Star Trek IV: The Voyage Home, the starship Enterprise flies on a trajectory that passes close to the Sun’s surface. What features should a real spaceship have to survive such a flight? Why?

Question 9.3

Discuss some of the difficulties in correlating solar activity with changes in Earth’s climate.

Question 9.4

Describe some of the advantages and disadvantages of observing the Sun (a) from space and (b) from Earth’s south pole. What kinds of phenomena and issues might solar astronomers want to explore from these locations?

Collaborative exercises

Question 9.1

Figure 9-16 shows variations in the average latitude of sunspots. Estimate the average latitude of sunspots in the year you were born and estimate the average latitude on your twenty-first birthday. Make rough sketches of the Sun during those years to illustrate your answers.

Question 9.2

Create a diagram showing a sketch of how limb darkening on the Sun would look different if the Sun had either a thicker or thinner photosphere. Be sure to include a caption explaining your diagram.

Question 9.3

Solar granules, shown in Figure 9-6, are about 600 miles (1000 km) across. What city is about that distance away from where you are right now? What city is that distance from the birthplace of each group member?

Question 9.4

Magnetic arches in the corona are shown in Figure 9-20. How many Earths high are these arches, and how many Earths could fit inside one arch?

Observing Questions

Question 9.1

Use the Starry Night™ program to examine simulations of various features that appear on the surface of the Sun. Select Favourites > Explorations > Solar Surface to show a simulated view of the visible surface of the Sun as it might appear from a spacecraft. Stop Time Flow and use the location scroller to examine this surface. (a) Which layer of the Sun’s atmosphere is shown in this part of the simulation? (b) List the different features that are visible in this view of the Sun’s surface. (c) Click and hold the Decrease current elevation button in the toolbar to move to a location on the surface of the Sun, from which you can look out into the chromosphere. (The Viewing Location panel will indicate the location on the Sun’s surface.) This simulated view of the chromosphere is at the color of the Balmer-α wavelength of hydrogen light. The opacity of the gas at this wavelength means that you can see the structure of the hot chromosphere that lies above the visible surface. Use the hand tool or cursor keys to change the gaze direction to view different features of the Sun, zooming in when necessary for a closer look at features on the horizon. (d) Provide a detailed description of the various features visible in this simulation of the Sun’s surface. You can see current solar images from both ground- and space-based solar telescopes by opening the LiveSky pane if you have an Internet connection on your computer.

Question 9.1

Use Starry Night™ to measure the Sun’s rotation. Select Favourites > Explorations > Solar Rotation to display the Sun as seen from about 0.008 AU above its surface, well inside the orbit of Mercury. Use the Time controls to stop the Sun’s rotation at a time when a line of longitude on the Sun makes a straight line between the solar poles, preferably a line crossing a recognizable solar feature. Note the date and time. Run Time Forward and adjust the date and time to place this selected meridian in this position again. (a) What is the rotation rate of the Sun as shown in Starry Night™? This demonstration does not show one important feature of the Sun, namely its differential rotation, where the equator of this fluid body rotates faster than the polar regions. (b) To which region of the Sun does your measured rotation rate refer?