Question 10.1

Describe the features of the Sun’s atmosphere that are always present.

Question 10.2

Describe the three main layers of the solar atmosphere and how you would best observe them.

Question 10.3

Name and describe seven features of the active Sun. Which two are the same, seen from different angles?

Question 10.4

Describe the three main layers of the Sun’s interior.

Question 10.5

*When will the next sunspot minimum and sunspot maximum occur after the maximum in 2013 and the minimum in 2007? Explain your reasoning.

Question 10.6

Why is the solar cycle said to have a period of 22 years, even though the sunspot cycle is only 11 years long?

Question 10.7

How do astronomers detect the presence of a magnetic field in hot gases, such as the field in the solar photosphere?

Question 10.8

Describe the dangers in attempting to observe the Sun. How have astronomers learned to circumvent these hazards?

Question 10.9

Give an everyday example of hydrostatic equilibrium not presented in the book.

Question 10.10

Give some everyday examples of heat transfer by convection and radiative transport.

Question 10.11

What do astronomers mean by a “model of the Sun”?

Question 10.12

Why do thermonuclear reactions in the Sun take place only in its core?

Question 10.13

What is hydrogen fusion? This process is sometimes called “hydrogen burning.” How is hydrogen burning fundamentally unlike the burning of a log in a fireplace?

Question 10.14

Describe the Sun’s interior, including the main physical processes that occur at various levels within the Sun.

Question 10.15

What is a neutrino, and why are astronomers so interested in detecting neutrinos from the Sun?

Question 10.16

*Using the mass and size of the Sun, calculate the Sun’s average density. Compare your answer to the average densities of the outer planets. (Hint: The volume of a sphere of radius r is πr³.)

Question 10.17

*Assuming that the current rate of hydrogen fusion in the Sun remains constant, what percent of the Sun’s mass will be converted into helium over the next 5 billion years? How will this affect the chemical composition of the Sun?

Question 10.18

*Calculate the wavelengths at which the photosphere, chromosphere, and corona emit the most radiation. Explain how the results of your calculations suggest the best way to observe these regions of the solar atmosphere. (Hint: Use Wien’s law and assume that the average temperatures of the photosphere, chromosphere, and corona are 5800 K, 50,000 K, and 1.5 × 10⁶ K, respectively.)

Question 10.19

When we are near a sunspot maximum, the Hubble Space Telescope must be moved to a higher orbit. Why? (Hint: Think about how the increased solar energy affects Earth’s atmosphere.)

Question 10.20

Explain how the Sun can be emitting more energy today than shortly after it formed even though its surface temperature has remained roughly constant.

Question 10.21

Discuss the extent to which cultures around the world have worshiped the Sun as a deity throughout history. Why do you think our star inspires such wide-spread veneration?

Question 10.22

Discuss some of the difficulties of correlating solar activity with changes in the terrestrial climate.

Question 10.23

Describe some advantages and disadvantages of observing the Sun (a) from space and (b) from Earth’s South Pole. What kinds of phenomena and issues do solar astronomers want to explore from both Earth-orbiting and Antarctic observatories?

Question 10.24

The Sun were not rotating? What about it would be different?

Question 10.25

The typical solar wind were much stronger (say, 100 times stronger) than it is now? What differences would there be in the solar system?

Question 10.26

The typical solar wind were much weaker (say, 100 times weaker) than it is now? What differences would there be in the solar system?

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Question 10.27

The Sun’s brightness and heat output periodically changed, as they do in many stars? What differences would there be in the solar system? Unless your instructor gives you another time frame, assume that the light and heat vary together in a cycle that lasts 1 year.

Question 10.28

Search the Web for all solar neutrino experiments. Make a list of them and indicate which are currently operating and which are still under construction. Summarize the results found by the active detectors.

Question 10.29

Search the Web for information about features of the solar atmosphere called sigmoids. What are they? What causes them? How do sigmoids provide a way to predict coronal mass ejections?

Question 10.30

Determining the Lifetime of a Solar Granule. Access and view the video “Granules on the Sun’s Surface” in Chapter 10 of the Discovering the Universe Web site. You will use it to determine the approximate lifetime of a solar granule. Select an area on the Sun’s image and slowly and rhythmically repeat Start, Stop, Start, Stop until you can consistently predict the appearance and disappearance of granules. While keeping your rhythm, move to a different area of the video and continue monitoring the appearance and disappearance of granules. When you are confident that you have the timing right, move your eyes to the clock shown in the video (or work with a partner). Using your Start-Stop cycle, determine the length of time between the appearance and disappearance of the granules and record your answer.

Question 10.31

Does the Sun shine by burning gas, like methane? Justify your answer.

Question 10.32

What causes sunspots?

Question 10.33

Does the Sun rotate? Justify your answer.

Question 10.34

Does the Sun have a solid or liquid surface, like the Earth?

Question 10.35

Does the Sun have an atmosphere? Explain your reasoning.

Question 10.36

Use a telescope to view the Sun, but ONLY when it is equipped with an appropriate and safe solar filter, or by projecting the Sun’s image onto a screen or sheet of white paper. Do not look directly at the Sun! Looking at the Sun causes blindness. Do you see any sunspots? If so, sketch their appearance. Can you distinguish between the umbrae and penumbrae of the sunspots? Can you see limb darkening? Can you see granulation?

Question 10.37

If you have access to a telescope equipped with a special Hα filter, specifically designed for viewing the Sun safely at the color of the Balmer-alpha hydrogen spectral line, use this instrument to examine the solar surface. How does the filtered appearance of the Sun differ from that in white light (see Question 36)? What do sunspots look like in H_α? Can you see any prominences? Can you see any filaments? Are the filaments in the H_α image close to any sunspots seen in white light?

Question 10.38

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™? Note that 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? It is this differential rotation that is thought to generate the magnetic fields and active regions that make the Sun an active star. Occasional emission of high-energy particles from these active regions can disturb the Earth’s environment and disrupt electrical transmission systems. Examine this image of the Sun and compare it to real images seen in textbooks, the Internet, or from the links in the Solar Images layer in the LiveSky pane. (c) In particular, how does the distribution of sunspots and active regions on this image compare to the distribution of these regions on the real sun?

Question 10.39

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. 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 wavelength of the Balmer-alpha spectral line of hydrogen. 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. (c) 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 spacebased solar telescopes by opening the LiveSky pane if you have an Internet connection on your computer.