stellar astronomy phy2009

openstax questions, msp 2026

5.1 What distinguishes one type of electromagnetic radiation from another? What are the main categories (or bands) of the electromagnetic spectrum?

5.2
What is a wave? Use the terms wavelength and frequency in your definition.

5.3 Is your textbook the kind of idealized object (described in section on radiation laws) that absorbs all the radiation falling on it? Explain. How about the black sweater worn by one of your classmates?

5.4 Where in an atom would you expect to find electrons? Protons? Neutrons?

5.5 Explain how emission lines and absorption lines are formed. In what sorts of cosmic objects would you expect to see each?

5.6 Explain how the Doppler effect works for sound waves and give some familiar examples.

5.7 What kind of motion for a star does not produce a Doppler effect? Explain.

5.8 Describe how Bohr’s model used the work of Maxwell.

5.9 Explain why light is referred to as electromagnetic radiation.

5.10 Explain the difference between radiation as it is used in most everyday language and radiation as it is used in an astronomical context.

5.11 What are the differences between light waves and sound waves?

5.12 Which type of wave has a longer wavelength: AM radio waves (with frequencies in the kilohertz range) or FM radio waves (with frequencies in the megahertz range)? Explain.

5.15 Which is more dangerous to living things, gamma rays or X-rays? Explain.

5.16 Explain why we have to observe stars and other astronomical objects from above Earth’s atmosphere in order to fully learn about their properties.

5.17 Explain why hotter objects tend to radiate more energetic photons compared to cooler objects.

5.18 Explain how we can deduce the temperature of a star by determining its color.

5.19 Explain what dispersion is and how astronomers use this phenomenon to study a star’s light.

5.20 Explain why glass prisms disperse light.

5.21 Explain what Joseph Fraunhofer discovered about stellar spectra.

5.22 Explain how we use spectral absorption and emission lines to determine the composition of a gas.

5.23 Explain the results of Rutherford’s gold foil experiment and how they changed our model of the atom.

5.24 Is it possible for two different atoms of carbon to have different numbers of neutrons in their nuclei? Explain.

5.25 What are the three isotopes of hydrogen, and how do they differ?

5.26 Explain how electrons use light energy to move among energy levels within an atom.

5.27 Explain why astronomers use the term “blueshifted” for objects moving toward us and “redshifted” for objects moving away from us.

5.28 If spectral line wavelengths are changing for objects based on the radial velocities of those objects, how can we deduce which type of atom is responsible for a particular absorption or emission line?

5.30 With what type of electromagnetic radiation would you observe:

1. A star with a temperature of 5800 K?

2. A gas heated to a temperature of one million K?

3. A person on a dark night?

5.31 Why is it dangerous to be exposed to X-rays but not (or at least much less) dangerous to be exposed to radio waves?

5.32 Go outside on a clear night, wait 15 minutes for your eyes to adjust to the dark, and look carefully at the brightest stars. Some should look slightly red and others slightly blue. The primary factor that determines the color of a star is its temperature. Which is hotter: a blue star or a red one? Explain

5.33 Water faucets are often labeled with a red dot for hot water and a blue dot for cold. Given Wien’s law, does this labeling make sense?

5.34 Suppose you are standing at the exact center of a park surrounded by a circular road. An ambulance drives completely around this road, with siren blaring. How does the pitch of the siren change as it circles around you?

5.35 How could you measure Earth’s orbital speed by photographing the spectrum of a star at various times throughout the year? (Hint: Suppose the star lies in the plane of Earth’s orbit.)

5.36 Astronomers want to make maps of the sky showing sources of X-rays or gamma rays. Explain why those X-rays and gamma rays must be observed from above Earth’s atmosphere.

5.37 The greenhouse effect can be explained easily if you understand the laws of blackbody radiation. A greenhouse gas blocks the transmission of infrared light. Given that the incoming light to Earth is sunlight with a characteristic temperature of 5800 K (which peaks in the visible part of the spectrum) and the outgoing light from Earth has a characteristic temperature of about 300 K (which peaks in the infrared part of the spectrum), explain how greenhouse gases cause Earth to warm up. As part of your answer, discuss that greenhouse gases block both incoming and outgoing infrared light. Explain why these two effects don’t simply cancel each other, leading to no net temperature change.

5.38 An idealized radiating object does not reflect or scatter any radiation but instead absorbs all of the electromagnetic energy that falls on it. Can you explain why astronomers call such an object a blackbody? Keep in mind that even stars, which shine brightly in a variety of colors, are considered blackbodies. Explain why.

5.39 Why are ionized gases typically only found in very high-temperature environments?

5.40 Explain why each element has a unique spectrum of absorption or emission lines.

15.2 Describe how energy makes its way from the nuclear core of the Sun to the atmosphere. Include the name of each layer and how energy moves through the layer.

15.3 Make a sketch of the Sun’s atmosphere showing the locations of the photosphere, chromosphere, and corona. What is the approximate temperature of each of these regions?

15.4 Why do sunspots look dark?

15.5 Which aspects of the Sun’s activity cycle have a period of about 11 years? Which vary during intervals of about 22 years?

15.6 Summarize the evidence indicating that over several hundreds of years or more there have been variations in the level of the solar activity.

15.7 What is the Zeeman effect and what does it tell us about the Sun?

15.8 Explain how the theory of the Sun’s dynamo results in an average 22-year solar activity cycle. Include the location and mechanism for the dynamo.

15.9 Compare and contrast the four different types of solar activity above the photosphere.

15.13 Table 15.1 indicates that the density of the Sun is 1.41 g/cm³. Since other materials, such as ice, have similar densities, how do you know that the Sun is not made of ice?

15.14 Starting from the core of the Sun and going outward, the temperature decreases. Yet, above the photosphere, the temperature increases. How can this be?

15.15 Since the rotation period of the Sun can be determined by observing the apparent motions of sunspots, a correction must be made for the orbital motion of Earth. Explain what the correction is and how it arises. Making some sketches may help answer this question.

15.16 Suppose an (extremely hypothetical) elongated sunspot forms that extends from a latitude of 30° to a latitude of 40° along a fixed line of longitude on the Sun. How will the appearance of that sunspot change as the Sun rotates? (Figure 15.17 should help you figure this out.)

15.17 The text explains that plages are found near sunspots, but Figure 15.18 shows that they appear even in areas without sunspots. What might be the explanation for this?

15.18 Why would a flare be observed in visible light, when they are so much brighter in X-ray and ultraviolet light?

15.19 How can the prominences, which are so big and ‘float’ in the corona, stay gravitationally attached to the Sun while flares can escape?

16.1 How do we know the age of the Sun?

16.2 Explain how we know that the Sun’s energy is not supplied either by chemical burning, as in fires here on Earth, or by gravitational contraction (shrinking).

16.3 What is the ultimate source of energy that makes the Sun shine?

16.4 What are the formulas for the three steps in the proton-proton chain?

16.5 How is a neutrino different from a neutron? List all the ways you can think of.

16.6 Describe in your own words what is meant by the statement that the Sun is in hydrostatic equilibrium.

16.7 Two astronomy students travel to South Dakota. One stands on Earth’s surface and enjoys some sunshine. At the same time, the other descends into a gold mine where neutrinos are detected, arriving in time to detect the creation of a new radioactive argon nucleus. Although the photon at the surface and the neutrinos in the mine arrive at the same time, they have had very different histories. Describe the differences.

16.8 What do measurements of the number of neutrinos emitted by the Sun tell us about conditions deep in the solar interior?

16.9 Do neutrinos have mass? Describe how the answer to this question has changed over time and why.

16.10 Neutrinos produced in the core of the Sun carry energy to its exterior. Is the mechanism for this energy transport conduction, convection, or radiation?

16.11 What conditions are required before proton-proton chain fusion can start in the Sun?

16.12 Describe the two main ways that energy travels through the Sun.

16.16 A friend who has not had the benefit of an astronomy course suggests that the Sun must be full of burning coal to shine as brightly as it does. List as many arguments as you can against this hypothesis.

16.17 Which of the following transformations is (are) fusion and which is (are) fission: helium to carbon, carbon to iron, uranium to lead, boron to carbon, oxygen to neon? (See Appendix K for a list of the elements.)

16.18 Why is a higher temperature required to fuse hydrogen to helium by means of the CNO cycle than is required by the process that occurs in the Sun, which involves only isotopes of hydrogen and helium?

16.19 Earth’s atmosphere is in hydrostatic equilibrium. What this means is that the pressure at any point in the atmosphere must be high enough to support the weight of air above it. How would you expect the pressure on Mt. Everest to differ from the pressure in your classroom? Explain why.

16.20 Explain what it means when we say that Earth’s oceans are in hydrostatic equilibrium. Now suppose you are a scuba diver. Would you expect the pressure to increase or decrease as you dive below the surface to a depth of 200 feet? Why?

16.21 What mechanism transfers heat away from the surface of the Moon? If the Moon is losing energy in this way, why does it not simply become colder and colder?

16.22 Suppose you are standing a few feet away from a bonfire on a cold fall evening. Your face begins to feel hot. What is the mechanism that transfers heat from the fire to your face? (Hint: Is the air between you and the fire hotter or cooler than your face?)

16.23 Give some everyday examples of the transport of heat by convection and by radiation.

16.24 Suppose the proton-proton cycle in the Sun were to slow down suddenly and generate energy at only 95% of its current rate. Would an observer on Earth see an immediate decrease in the Sun’s brightness? Would she immediately see a decrease in the number of neutrinos emitted by the Sun?

16.25 Do you think that nuclear fusion takes place in the atmospheres of stars? Why or why not?

16.26 Why is fission not an important energy source in the Sun?

16.27 Why do you suppose so great a fraction of the Sun’s energy comes from its central regions? Within what fraction of the Sun’s radius does practically all of the Sun’s luminosity originate (see Figure 16.16)? Within what radius of the Sun has its original hydrogen been partially used up? Discuss what relationship the answers to these questions bear to one another.

16.28 Explain how mathematical computer models allow us to understand what is going on inside of the Sun.