SCCC 115 - Honor's Descriptive Astronomy
Exam 3
Prof. Lacey
15 November 2005

Circle the correct answer to the following multiple choice questions. Each question is worth 2 points.

1. Which of the following is true about the seasons on Uranus?
   1. The seasons on Uranus are not unlike those on Earth or Mars.
   2. The uranian rotation axis produces some extreme seasonal effects.
   3. Like Jupiter, Uranus has little tilt, with its equator always facing the Sun.
   4. From the uranian equator, the Sun would remain stationary all the time.
   5. Uranus' weather will become less turbulent as equinox approaches in 2010.
   Answer: B Page Ref: 13.3R

2. None of the ring systems now observed are permanent, so there must be some recurring mechanism which rebuilds them.
   1. True
   2. False
   Answer: TRUE Page Ref: 13.7N

3. Unlike other planets, in neither Uranus or Neptune does the magnetic field come anywhere close to aligning with the axis of rotation.
   1. True
   2. False
   Answer: True Page Ref: 13.5N

4. How did Mercury's location in the solar system affect its composition?
   1. Mercury is rich in metals because only metallic grains could survive the high temperatures so near the Sun.
   2. Mercury is more volatile than most metals, so formed closer to the hot Sun.
   3. Mercury is poor in metals because metallic grains could not survive the high temperatures so near the Sun.
   4. The nearby Sun caused ice in Mercury's interior to melt into liquid water.
   5. Because Mercury is so near the Sun, its composition is similar to the Sun; mostly hydrogen and helium.
   Answer: A Page Ref: 15.2R

5. The orbits of most comets:
   1. are like the planets, fairly circular and in the ecliptic plane.
   2. lie almost entirely beyond the orbit of Neptune.
   3. have perihelions within the orbits of Mercury.
   4. go no farther out than Pluto, then return to the sun again.
   5. are shorter than the 76 year period for Comet Halley.
   Answer: B Page Ref: 14.2R

6. The type of asteroid that would be the densest would be type:
   1. C.
   2. M.
   3. S.
   4. V.
   5. Z.
   Answer: B Page Ref: 14.1N

7. The "solar constant" refers to the observation that the Sun's brightness does not ever change.
   1. True
   2. False
   Answer: FALSE Page Ref: 16.1

8. Why are the jovian planets so large?
   1. They formed from the largest protoplanets which swept gas from the solar nebula.
   2. The gas and dust were hotter in the outer regions, making it easier for the planets to form.
   3. They started out as stars, but lost most of their mass through fusion.
   4. The jovian planets are normal in size; the terrestrial planets were just as large but the Sun's heat reduced their size.
   5. The jovian planets are at least a billion years older than the terrestrial planets and have constantly gained matter from comets.
   Answer: A Page Ref: 15.2R

9. What is it about the Sun's corona that astronomers don't understand?
   1. No one knows why that part of the Sun's atmosphere does not drift away into space.
   2. During total solar eclipses, the corona sometimes disappears from view.
   3. The corona seems to absorb 2/3 of the neutrinos that pass thorough it.
   4. The corona is much hotter than layers of the Sun that are closer to the solar interior.
   5. The Sun's corona extends to the outer reaches of the solar system.
   Answer: D Page Ref: 16.4R

10. What happens when a solar nebula contracts?
    1. It flattens out.
    2. It spins faster.
    3. It heats up.
    4. all of the above
    5. none of the above
    Answer: D Page Ref: 15.1R

11. In terms of composition:
    1. each planet is unique, with no similarities among them.
    2. all the planets are made of the same elements, and in the same proportions.
    3. the jovians are much more like the sun than are the terrestrials.
    4. the terrestrials are similar to the sun, for they formed closer to it.
    5. the sun is unique in having far more light elements than any of the planets do.
    Answer: C Page Ref: 15.2R

12. Sunspots are the magnetic poles of strong solar magnetic storms.
    1. True
    2. False
    Answer: TRUE Page Ref: 16.5N

13. Which of the following is NOT a property of neutrinos?
    1. can change forms in the eight minutes from the Sun's core to us
    2. almost massless
    3. can travel very close to the speed of light
    4. neutral in charge
    5. cannot interact at all with normal matter
    Answer: E Page Ref: 16.6R

14. The Oort Cloud is thought to be:
    1. the cloud of gas and dust from which our solar system formed.
    2. a cloud of debris that occasionally encounters the Earth, causing a meteor shower.
    3. the spherical cloud of comets and some larger icy bodies surrounding the outer solar system.
    4. a cloud of asteroids moving between the orbits of Mars and Jupiter.
    5. the material in the ecliptic plane that creates the zodiacal light.
    Answer: C Page Ref: 14.2R

15. What factor caused different planets to form out of different types of material?
    1. the angular momentum of the forming planet
    2. the quantity of dust particles in the solar nebula
    3. the variation in temperature throughout the solar nebula
    4. all of the above
    5. none of the above
    Answer: C Page Ref: 15.1R

16. The first visible hint to the solar wind's existence came from observations of the tails of comets as they rounded the Sun.
    1. True
    2. False
    Answer: TRUE Page Ref: 16.4N

17. What causes a meteor shower?
    1. The solar wind chills the plasma and causes it to condense into particles.
    2. Earth intercepts a stray swarm of asteroids left by a collision.
    3. Earth crosses the orbit of an old comet, whose orbit is littered with debris.
    4. Earth encounters the asteroid belt when Mars' gravity pushes it toward us.
    5. A small constellation of dying stars disintegrates.
    Answer: C, Page Ref: 14.3R

    
    
    Answer the remaining problems and answer each question on a separate sheet of paper. Remember to use only significant figures in the answers and show all work! Remember to include units for all answers.
    
    
    

18. (6 pts) How do we know the age of the solar system is 4.6 billion years old?

    Radioactive dating of asteroids and moons rocks show that the material formed at least 4.6 billion years ago.

19. (6 pts) Name three (3) examples in our solar system that are believed to be the results of catastrophes that occurred during the formation of solar system formation.

    Tilt of uranus

    Retrograde rotation of Venus, Pluto, and Uranus

    Retrograde orbits of Uranus's moons

    Moon's formation

20. (10 pts) What are comets made of?

    silicates and rocky dust

    metallic dust particles

    dark colored complex hydrocarbons

    methane, ammonia, and water ice

21. The color and luminosity of a star depends on the temperature of the photosphere.
    1. (3 pts) If the Sun's temperature doubles, how many times greater or lesser is the new peak wavelength?
       

       $\lambda \propto \frac{1}{T}$,
       

       So if the temperature, T, doubles, then new $\lambda \propto \frac{1}{new ~T}=\frac{1}{2T_\odot}=1/2 \lambda_\odot$. So the peak wavelength of the Sun would decrease by a factor of 1/2 .

    2. (3 pts) If the Sun's temperature doubles, how many times greater or lesser is the new luminosity of the Sun?
       

       $L \propto T^4 ~R^2$,
       

       So if the temperature, T, doubles, then new $T = 4T_\odot = 16 T_\odot =16~T_\odot$. So the luminosity of the Sun would increase by 16 times.

    3. (6 pts) If the Sun's temperature doubles, the hydrogen absorption lines in the Sun's spectrum become less prominent. Explain why this happens?
       

       The temperature becomes too hot. The radiation from the Sun has an energy that is high enough to ionize (remove) the electron from the hydrogen nucleus, which is just a proton. If most of the hydrogen is ionized, then there are no electrons on the hydrogen to become excited as they absorb the radiation from the Sun's core, which creates the absorption lines.

22. List 6 observed properties of our solar system that any solar system formation theory, such as the solar nebula theory of formation, must explain.

    All planets orbit in roughly the same plane

    All planets orbit in the same direction around the sun

    Terrestrial planets are rocky, small and found near the Sun

    Jovian planets are large, gaseous and found far from the Sun