Questions to Review for the 2Nd Midterm

Questions to review for the 2nd Midterm

Ch. 8 Problems

1. Solar System Trends. Study the planetary data in Table 8.1 to answer each of the following.

a. Notice the relationship between distance from the Sun and surface temperature. Describe the trend, explain why it exists, and explain any notable exceptions to the trend.

b. The text says that planets can be classified as either terrestrial or jovian, with Pluto as a misfit. Describe in general how the columns for density, composition, and distance from the Sun support this classification.

c. Which column would you use to find out which planet has the shortest days? Do you see any notable differences in the length of a day for the different types of planet? Explain.

d. Describe the trend you see in orbital periods and explain the trend in terms of Kepler's third law.

e. Which planets would you expect to have seasons? Why?

f. Which column tells you how much a planet's orbit deviates from a perfect circle? Based on that column, are there any planets for which you would expect the surface temperature to vary significantly over the course of each orbit? Explain.

g. By studying the table data, briefly describe how escape velocity is related to mass and radius. Is the trend what you expect based on what you learned about escape velocity in Chapter 5?

h. Suppose you weigh 100 pounds. State how much you would weigh on each of the other planets in our solar system. (Hint: Recall from Chapter 5 that weight is mass times the acceleration of gravity. The surface gravity column tells you how the acceleration of gravity on other planets compares to that on Earth.)

1 2. Left Out in the Cold. In what ways does Pluto resemble a terrestrial planet? In what ways does it resemble a jovian planet? In what ways does it resemble neither?

3. Comparing Leftovers. Apart from their orbital properties, how are comets different from asteroids? Which are more numerous, comets or asteroids?

4. Patterns of Motion. In one or two paragraphs, explain why the existence of orderly patterns of motion in our solar system should suggest that the Sun and the planets all formed at one time from one cloud of gas, rather than as individual objects at different times.

5. Two Classes of Planets. In terms a friend or roommate would understand, write one or two paragraphs explaining why we say that the planets fall into two major categories and what those categories are.

Chapter 9

Surprising Discoveries? Suppose we make the discoveries described below. (These are not real discoveries.) Decide whether each discovery should be considered reasonable or surprising. Explain. (In some cases both views can be defended.)

1. A solar system has ten planets that all orbit the star in approximately the same plane. However, five planets orbit in one direction (e.g., counterclockwise), while the other five orbit in the opposite direction (e.g., clockwise).

Problems

2. Ingredients of the Planets. Describe the four categories of materials in the solar nebula by their condensation properties and abundance. Which ingredients are present in terrestrial planets? In jovian planets?

3. Solar Wind. What is the solar wind, and what roles did it play in the early solar system?

4. The Beginning of Our Solar System? What evidence suggests that a nearby stellar explosion may have triggered the collapse of the solar nebula?

2 5. A Cold Solar Nebula. Suppose the entire solar nebula had cooled to 50 K before the solar wind cleared it away. How would the composition and sizes of the planets of the inner solar system be different from what we see today? Explain your answer in a few sentences.

6. No Gas Capture. Suppose the solar wind had cleared away the solar nebula before the seeds of the jovian planets could gravitationally draw in hydrogen and helium gas. How would the planets of the outer solar system be different? Would they still have many moons? Explain your answer in a few sentences.

7. Carbon-14 Dating. The half-life of carbon-14 is about 5,700 years.

a. You find a piece of cloth painted with organic dye. By analyzing the dye, you find that only 77% of the carbon-14 originally in the dye remains. When was the cloth painted? (VERY ROUGHLY)

8. Dating Lunar Rocks. You are analyzing Moon rocks that contain small amounts of uranium-238, which decays into lead with a half-life of about 4.5 billion years.

In a rock from the lunar highlands, you determine that 55% of the original uranium-238 remains, while the other 45% has decayed into lead. How old is the rock? VERY ROUGHLY Chapter 10

1. The next mission to Mercury photographs part of the surface never seen before and detects vast fields of sand dunes.

2. New orbital photographs of craters on Mars that have gullies also show pools of liquid water to be common on the crater bottoms.

3. Clear-cutting in the Amazon rain forest on Earth exposes vast regions of ancient terrain that is as heavily cratered as the lunar highlands.

4. Drilling into the Martian surface, a robotic spacecraft discovers liquid water a few meters beneath the slopes of a Martian volcano.

Problems

5. Planetary Geology. Define the term planetary geology in everyday terms. Why do we believe that differences between planetary surfaces can be traced to fundamental properties (size, distance from the Sun, rotation) instead of random occurrences that only affected individual planets?

3 6. Seeing Inside. Briefly explain how we learn about planetary interiors.

7. Understanding Interiors. What is differentiation, and how did it lead to the core-mantle-crust structures of the terrestrial worlds? What is a lithosphere, and why is it geologically important? Describe the conditions under which convection occurs. What is mantle convection, and how is it related to lithospheric thickness?

8. Clues from Craters. Describe what we can learn from impact craters. How is crater crowding related to surface age?

9. Volcano Vocabulary. What is outgassing, and how is it important to our existence?

10. Tectonics Terms. What do we mean by plate tectonics,? Describe how mantle convection can make different kinds of features on a planet's surface.

11. Earth vs. Moon. Why is the Moon heavily cratered, but not Earth? Explain in one or two paragraphs, relating your answer back to their fundamental properties.

12. Comparative Erosion. Consider erosion on Mercury, Venus, the Moon, and Mars. Which of these four worlds has the greatest erosion? Why? For each world, write a paragraph explaining its level of erosion, tracing it back to fundamental properties.

Dating Planetary Surfaces. We have discussed two basic techniques for determining the age of a planetary surface: studying the abundance of impact craters and radiometric dating of surface rocks. Which technique seems more reliable? Which technique is more practical? Explain.

Chapter 11

True or False? Decide whether each of the following statements is true or false. Explain your reasoning.

1. If Earth rotated faster, hurricanes would be more common and more severe.

4 2. Mars would still have seasons even if its orbit around the Sun were perfectly circular rather than elliptical.

3. If the solar wind were much stronger, Mercury might develop a carbon dioxide atmosphere.

4. If Earth had as much carbon dioxide in its atmosphere as Venus, our planet would be too hot for liquid water to exist on the surface.

Problems

5. Blue Skies Everywhere? Briefly explain why the sky is blue on Earth and why it is not blue on Venus or Mars.

6. The Thinnest Atmospheres. What is the origin of the very thin atmospheres of the Moon and Mercury? How might it be possible for these worlds to have water ice in polar craters?

7. Magic Mercury. Suppose we could magically give Mercury the same atmosphere as Earth. Assuming this magical intervention happened only once, would Mercury be able to keep its new atmosphere? Explain.

8. Sources and Losses. Choose one process by which atmospheres can gain gas and one by which they can lose gas. For each process, write a few sentences that describe it and how it depends on each of the following fundamental planetary properties: size, distance from the Sun, and rotation rate.

Chapter 12

1. Saturn's core is pockmarked with impact craters and dotted with volcanoes erupting basaltic lava.

2. Neptune's deep blue color is not due to methane, as previously thought, but instead is due to its surface being covered with an ocean of liquid water.

3. An extrasolar planet is discovered that is made primarily of hydrogen and helium. It has approximately the same mass as Jupiter but is the same size as Neptune.

4. A new small moon is discovered to be orbiting Jupiter. It is smaller than any other of Jupiter's moons but has several large, active volcanoes.

5 Problems

5. Jovian Planet Interiors. Briefly summarize the techniques we use to study the interiors of the jovian planets. Briefly describe the internal heat sources of each of the four jovian planets.

6. Comparing Jovian Planet Atmospheres. Briefly describe Jupiter's global circulation and weather

7. Jovian Planet Moons. Briefly describe how we categorize jovian moons by size. What is the origin of most of the medium and large moons? What is the origin of many of the small moons?

8. Unusual Moons. Describe the atmosphere of Titan. What evidence suggests that Titan may have oceans of liquid ethane? Describe Triton and explain why we think it is a captured moon.

9. The Great Red Spot. Based on the infrared and visible images in Figure 12.8, is Jupiter's Great Red Spot warmer or cooler than nearby clouds? Does this mean it is higher or lower in altitude than the nearby clouds? Explain.

10. Minor Ingredients Matter. Suppose the jovian planet atmospheres were composed 100% of hydrogen and helium rather than 98% of hydrogen and helium. How would the atmospheres be different in terms of color and weather? Explain.

Chapter 13

1. A small asteroid that orbits within the asteroid belt has an active volcano.

2. Scientists discover a meteorite that, based on radiometric dating, is 7.9 billion years old.

3. An object that resembles a comet in size and composition is discovered to be orbiting in the inner solar system.

Problems

6 4. Clues from the Leftovers. Why are comets, asteroids, and meteorites so useful to our understanding of the history of the solar system?

5. Space Rock or Earth Rock? How can we distinguish a meteorite from a terrestrial rock? Why do we find so many meteorites in Antarctica?

6. Meteor Showers. Explain how meteor showers are linked to comets. When is the best time of night to see meteor showers in general, and why?

7. Life Story of an Iron Atom. Imagine that you are an iron atom in a processed meteorite made mostly of iron that has recently fallen to Earth. Tell the story of how you got here, beginning from the time you were part of the gas in the solar nebula 4.6 billion years ago. Include as much detail as possible. Your story should be scientifically accurate but also creative and interesting.

Chapter 14 Questions and Exercises

This content can also be found in your book following the chapter Summary of Key Concepts

6. A fossil of an organism that died more than 300 million years ago, found in the crust near a mid-ocean ridge.

7. A “lost continent” on which humans had a great city just a few thousand years ago but that now resides deep underground near a subduction zone.

8. A planet in another solar system that has an Earth-like atmosphere with plentiful oxygen but no life of any kind.

9. A planet in another solar system that has an ozone layer but no ordinary oxygen (O2) in its atmosphere.

10. Evidence that the early Earth had more carbon dioxide in its atmosphere than Earth does today.

11. The discovery of life on Mars that also uses DNA as its genetic molecule and that uses a genetic code very similar to that used by life on Earth.

Problems

7 12. Building Continents. How are continents built up? Describe a few of the processes that have shaped North America.

13. Two Paths Diverged. Briefly explain why Earth has oceans and very little atmospheric carbon dioxide, while similar-size Venus has a thick carbon dioxide atmosphere.

14. Change in Formation Properties. Consider Earth's size, distance, composition, and rotation rate. Choose one property and suppose it had been different (e.g., smaller size or greater distance). Describe how this change might have affected Earth's subsequent history and the possibility of life on Earth.

15. Feedback Processes in the Atmosphere. As the Sun gradually brightens in the future, how can the CO2 cycle respond to reduce the warming effect? Which parts of the cycle will be affected? Is this an example of positive or negative feedback?

16. Ozone Signature. Suppose a powerful future telescope is able to take a spectrum of a terrestrial planet around another star. The spectrum reveals the presence of significant amounts of ozone. Why would this discovery strongly suggest the presence of life on this planet? Would it tell us whether the life is microbial or more complex? Summarize your answers in one or two paragraphs.

Chapter 15

Sensible Statements? Decide whether each of these statements is sensible and explain why it is or is not.

1. A sudden temperature rise in the Sun's core is nothing to worry about, because conditions in the core will soon return to normal.

2. If fusion in the solar core ceased today, worldwide panic would break out tomorrow as the Sun began to grow dimmer.

3. If you want to see lots of sunspots, just wait for solar maximum!

4. News of a major solar flare today caused concern among professionals in the fields of communications and electrical power generation.

5. By observing solar neutrinos, we can learn about nuclear fusion deep in the Sun's core.

Problems

8 6. Gravitational Contraction. Briefly describe how gravitational contraction generates energy and when it was important in the Sun's history.

7. Solar Characteristics. Briefly describe the Sun's luminosity, mass, radius, and average surface temperature.

8. Sunspots. What are sunspots? Why do they appear dark in pictures of the Sun?

9. Solar Fusion. What is the overall nuclear fusion reaction in the Sun? Briefly describe the proton-proton chain.

10. Models of the Sun. Explain how mathematical models allow us to predict conditions inside the Sun. How can we be confident that the models are on the right track?

11. Sun Quakes. How are “sun quakes” similar to earthquakes? How are they different? Describe how we can observe them and how they help us learn about the solar interior.

12. Energy Transport. Why does the energy produced by fusion in the solar core take so long to reach the solar surface? Describe the processes of radiative diffusion and convection in the solar interior.

13. The Photosphere. Describe the appearance and temperature of the Sun's photosphere. What is granulation? How would granulation appear in a movie?

14. Observing the Sun's Atmosphere. Why is the chromosphere best viewed with ultraviolet telescopes? Why is the corona best viewed with X-ray telescopes?

15. An Angry Sun. A Time magazine cover once suggested that an “angry Sun” was becoming more active as human activity changed Earth's climate through global warming. It's certainly possible for the Sun to become more active at the same time that humans are affecting Earth, but is it possible that the Sun could be responding to human activity? Can humans affect the Sun in any significant way? Explain.

16. Solar Power Collectors. This problem leads you through the calculation and discussion of how much solar power can be collected by solar cells on Earth.

a. Imagine a giant sphere surrounding the Sun with a radius of 1 AU. What is the surface area of this sphere, in square meters? (Hint: The formula for the surface area of a sphere is 4πr2).

9 b. Because this imaginary giant sphere surrounds the Sun, the Sun's entire luminosity of 3.8 x 1026 watts must pass through it. Calculate the power passing through each square meter of this imaginary sphere in watts per square meter. Explain why this number represents the maximum power per square meter that can be collected by a solar collector in Earth orbit.

c. List several reasons why the average power per square meter collected by a solar collector on the ground will always be less than what you found in part (b).

d. Suppose you want to put a solar collector on your roof. If you want to optimize the amount of power you can collect, how should you orient the collector? (Hint: The optimum orientation depends on both your latitude and the time of year and day.)

The Color of the Sun. The Sun's average surface temperature is about 5,800 K. Use Wien's law (see Mathematical Insight 6.2) to calculate the wavelength of peak thermal emission from the Sun. What color does this wavelength correspond to in the visible-light spectrum? In light of your answer, why do you think the Sun appears white or yellow to our eyes?

Chapter 16

True Statements? Decide whether each of the following statements is true or false and clearly explain how you know.

1. Two stars that look very different must be made of different kinds of elements.

2. Sirius is the brightest star in the night sky, but if we moved it 10 times farther away it would look only one-tenth as bright.

3. Sirius looks brighter than Alpha Centauri, but we know that Alpha Centauri is closer because its apparent position in the sky shifts by a larger amount as Earth orbits the Sun.

4. Stars that look red-hot have hotter surfaces than stars that look blue.

5. Some of the stars on the main sequence of the H—R diagram are not converting hydrogen into helium.

6. The smallest, hottest stars are plotted in the lower left-hand portion of the H—R diagram.

7. Stars that begin their lives with the most mass live longer than less massive stars because it takes them a lot longer to use up their hydrogen fuel.

8. Star clusters with lots of bright, blue stars are generally younger than clusters that don't have any such stars.

10 9. All giants, supergiants, and white dwarfs were once main-sequence stars.

10. Most of the stars in the sky are more massive than the Sun.

Problems

11. Similarities and Differences. What basic composition are all stars born with? Why do stars differ from one another?

12. Determining Parallax. Briefly explain how we calculate a star's distance in parsecs by measuring its parallax angle in arcseconds.

13. Deciphering Stellar Spectra. Briefly summarize the roles of Annie Jump Cannon and Cecilia Payne- Gaposchkin in discovering the spectral sequence and its meaning.

14. Eclipsing Binaries. Describe why eclipsing binaries are so important for measuring masses of stars.

15. Basic H—R Diagram. Draw a sketch of a basic Hertzsprung—Russell (H—R) diagram. Label the main sequence, giants, supergiants, and white dwarfs. Where on this diagram do we find stars that are cool and dim? Cool and luminous? Hot and dim? Hot and bright?

16. H—R Diagrams of Star Clusters. Explain why H—R diagrams look different for star clusters of different ages. How does the location of the main-sequence turnoff point tell us the age of the star cluster?

17. The Inverse Square Law for Light. Earth is about 150 million km from the Sun, and the apparent brightness of the Sun in our sky is about 1,300 watts/m2. Using these two facts and the inverse square law for light, determine the apparent brightness we would measure for the Sun if we were located at the following positions.

a. Half Earth's distance from the Sun.

b. Twice Earth's distance from the Sun.

c. Five times Earth's distance from the Sun.

11 18. Parallax and Distance. Use the parallax formula to calculate the distance to each of the following stars. Give your answers in both parsecs and light-years. a. Alpha Centauri: parallax angle of 0.7420.

b. Procyon: parallax angle of 0.2860.

Chapter 17 Questions and Exercises

This content can also be found in your book following the chapter Summary of Key Concepts

Sensible Statements? Decide whether each of these statements is sensible and explain why it is or is not.

1. The iron in my blood came from a star that blew up over 4 billion years ago.

2. A protostellar cloud spins faster as it contracts, even though its angular momentum stays the same.

3. When helium fusion begins in the core of a low-mass star, the extra energy generated causes the star's luminosity to rise.

4. I just discovered a 3.5MSun main-sequence star orbiting a 2.5MSun red giant. I'll bet that red giant was more massive than 3MSun when it was a main-sequence star.

5. If you could look inside the Sun today, you'd find that its core contains a much higher proportion of helium and a lower proportion of hydrogen than it did when the Sun was born.

Problems

Homes to Civilization? We do not yet know how many stars have Earth-like planets, nor do we know the likelihood that such planets might harbor advanced civilizations like our own. However, some stars can probably be ruled out as candidates for advanced civilizations. For example, given that it took a few billion years for humans to evolve on Earth, it seems unlikely that advanced life would have had time to evolve around a star that is only a few million years old. For each of the following stars, decide whether you think it is possible that it could harbor an advanced civilization. Explain your reasoning in one or two paragraphs.

6. A 10MSun main-sequence star.

7. A red supergiant.

12 8. Molecular Clouds. What is a molecular cloud? Briefly describe the process by which a protostar and protostellar disk form from gas in a molecular cloud.

9. Birth of a Close Binary. Under what conditions does a close binary form?

10. Protostellar Winds and Jets. Describe some of the activity seen in protostars, such as strong protostellar winds and jets.

11. Life Tracks. What do we mean by a star's life track on an H—R diagram? How does an H—R diagram that shows life tracks differ from a standard H—R diagram?

12. Degeneracy Pressure. What is degeneracy pressure? How does it differ from thermal pressure? Explain why degeneracy pressure can support a stellar core against gravity even when the core becomes very cold.

13. Hydrogen Shell Burning. What happens to the core of a star when it exhausts its hydrogen supply? Why does hydrogen shell burning begin around the inert core?

14. Helium Fusion. Why does helium fusion require much higher temperatures than hydrogen fusion? Briefly describe the overall reaction by which helium fuses into carbon.

15. Planetary Nebulae. What is a planetary nebula? What happens to the core of a star after a planetary nebula occurs?

16. Fate of the Sun. Briefly describe how the Sun will change, and how Earth will be affected by these changes, over the next several billion years.

17. Advanced Nuclear Burning. Describe some of the nuclear reactions that can occur in high-mass stars after they exhaust their core helium. Why does this continued nuclear burning occur in high-mass stars but not in low-mass stars?

18. Formation of the Elements. Summarize some of the observational evidence supporting our ideas about how the elements formed and showing that supernovae really occur.

13 Rare Elements. Lithium, beryllium, and boron are elements with atomic numbers 3, 4, and 5, respectively. Despite their being three of the five simplest elements, Figure 17.22 in the text shows that they are rare compared to many heavier elements. Suggest a reason for their rarity. (Hint: Consider the process by which helium fuses into carbon.)