ASTR 100 Chapter ReviewQuestions – Fall 2012 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX Section-1 Check the letter that represents the best answer to each of the multiple choice questions. Answer all questions in this section. Each question is worth 1 point. This section is worth 40 points. XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX 1. In the scientific method, a hypothesis _____. A. is a statement of fact B. makes a prediction that can be tested C. is usually proven to be correct D. can only be tested once E. none of these 2. Which of the following can't be considered an acceptable hypothesis?" A. Dark matter, (invisible matter which still has gravitational attraction), determines the orbits of stars in the the galaxy B. Mass increases with velocity C. Matter came into existence together with time D. The megagalaxies of the universe will become invisible to each other in time. E. all are acceptable hypotheses 3. A theory is an integrated explanation of numerous “proven”_____. A. facts B. laws C. controls D. hypotheses E. guesses 4. What is the correct sequence of steps in the scientific method? I. State a problem II. Analyze and interpret data III. Develop a hypothesis IV. Share the results with other scientists V. Design and perform experiment to test the hypothesis A. I – II - III - IV – V B. III – I - V – II – IV C. V – IV – III – II – I D. I – III – V – II – IV E. V – II – I – III - IV 5. Ptolemy's model sought to explain retrograde motion by _____. A. adding circles to epicycle orbits

B. adding circles to elliptical orbits C. adding epicycles to elliptical orbits

D. adding epicycles to circular orbits 6. Due to retrograde motion some planets will rise in the west and set in the east. True or False 7. Which of the following is correctly ordered from largest to smallest in size? A. Moon, neutron star, white dwarf, galaxy B. galaxy, white dwarf, Moon, neutron star, C. galaxy, planet, neutron star, white dwarf, D. galaxy, neutron star, Moon, white dwarf, 8. Inner planets have _____ than outer planets. A. lower densities B. higher densities C. thicker atmospheres D. higher masses 9. A main sequence star’s energy is normally generated by ____ . A. proton-proton fusion of hydrogen B. the fusion of hydrogen and helium C. both of the above D. neither of the above 10. Measurements indicate that a certain star has a very high intrinsic brightness (100,000 times as bright as the Sun. and yet is relatively cool (3500 K.. How can this be? A. The star must be in the upper part of the main sequence. B. The star must be very large. C. The star must be quite small. D. There must be an error in observation, because no star can have these properties. 11. Population II stars ____ than population I stars. A. have higher percentages of hydrogen and helium B. more likely found in the galactic halo C. give off more red light. D. all of the above 12. The average temperature at the surface of Venus is SUBSTANTIALLY greater than the average temperature at the surface of Earth because ____. A. it is much closer to the Sun B. it rotates more slowly and in a retrograde direction C. of the percentage of carbon dioxide in its thick atmosphere D. clouds of sulfuric acid in its atmosphere reflects sunlight back into space 13. Which of the following is NOT explained by the Solar Nebula theory? A. common revolution of Venus' orbit B. the rotation of Venus C. common age of Solar System objects

D. different composition of inner and outer planets 14. Suppose that in 2012 NASA's Kepler Mission discovers a series of planets with the following characteristics moving around a star that resembles our Sun : irregular, with solid surfaces; mean densities about that of H2O; radii less than 1000 m; no atmospheres. What would these planets be classified as, in comparison to our Solar System? A. Cometary nuclei B. Asteroids C. Terrestrial planets D. Jovian planets 15. A typical ____ galaxy has ____ than a typical ____ galaxy and therefore has ____ active star formation. A. elliptical, more gas and dust, spiral, more B. irregular, more gas and dust, elliptical, more C. elliptical, more gas and dust, spiral, less D. spiral, less gas and dust, elliptical, more 16. Newton's _____ provides an explanation for Kepler's laws of planetary motion. A. second law of motion B. first law of motion C. law of gravity D. third law of motion 17. Scientists estimate the Universe is about _____ old. A. 1.4 x 104 years B. 1.4 x 107 years C. 1.4 x 1010 years D. 1.4 x 1013 years 18. The Milky Way galaxy is no more than about 55,555 _____ in diameter. A. parsecs B. astronomical units C. light years D. solar diameters 19. The closest star to the Sun is a few ____ away. A. miles B. million light-years C. astronomical units D. parsecs 20. Our Solar System is only a few _____ in radius. A. light-years B. solar diameters C. light-hours D. light-seconds

21. The lifetime of a typical star of type A or type O is a few _____ years. A. thousand B. billion C. million D. hundred 22. Galaxies throughout the Universe appear to be distributed: A. mostly in a single spherical shell surrounding a void in space, presumed to have been caused by a vast explosion at the time of the Big Bang. B. uniformly throughout space. C. in groups and surfaces surrounding vast voids, much like the surfaces of giant bubbles. D. around a single point in space, the presumed location of the original Big Bang that created the Universe. 23. Current evidence indicates the Universe’s expansion ____. A. is speeding up B. is slowing down C. has stopped D. is constant 24. How far we can see into the universe is determined by A. the time since the beginning of the universe B. the speed of light C. the increasing power of new telescopes D. both A. and B. only 25. Which of the following play a role in creating the the elements found in the cores of terrestrial planets? A. high mass stars B. heavy element fusion C. supernovae D. all of the above 26. A successful theory of Solar System formation must be able to primarily explain: A. The fact that Mars has satellites. B. The fact that Pluto’s orbit is very elliptical. C. The fact that the planets all revolve in the same direction in the same direction. D. None of these, they're all accidents of history 27. Scientists can determine what a distant star is made of by looking at ____. A. its continuous spectrum B. its absorption spectrum C. similar stars D. samples obtained from the star

28. What is the distance of a galaxy with a recession speed of 280,000 km/sec? (use H = 70 km/sec/Mp C. A. 210,000 km/sec B. 4 Mpc C. 4,000 Mpc D. 140,000 km E. 7,000,000 km 29. A galaxy located at a distance D of 1 million light years away has an angular size A= 5 degree. What is the approximate diameter of this galaxy? (use d = 2 π A D / 360). A. 58,500 pc B. 87,000 light years C. 1 million light years D. 360,000 light years E. 6 million light years 30. Which particular property of the Cepheid variables makes them suitable as standard candles? A. Their pulsation period is related to their luminosity. B. Their luminosity is related to their mass. C. Their speed is related to the red shift of their spectral lines. D. They are very abundant in all galaxies. E. They are more likely to appear in the spiral arms of galaxies, and therefore clearly visible. 31. The distance of a faraway galaxy can be determined by: A. The parallax method B. Observation of Cepheid variable stars in that galaxy. C. Observation of quasars. D. Recessional velocity. E. The annual parallax. 32. What is the “rotation curve” of a galaxy? A. It is a graph of the orbital velocities at various distances from the center of the galaxy. B. t is a graph of the speed at the center of the galaxy. C. It is the recession speed of galaxies at various distances from the Milky Way.

D. It is the speed of the globular clusters in a galaxy. 33. In their search for dark matter, astronomers can exclude candidates whose presence is detectable Which of the following candidates can be ruled out? A. Black holes B. Neutrinos

C. Hot or cold gas D. Weakly Interacting Massive Particles (WIMPS). E. Dead white dwarfs 34. Which of the following statements about Quasars is not correct? A. Their spectra have the largest red-shifts observed. B. They are probably the most distant observable objects. C. They have abnormally high luminosities. D. Their cores are extremely large, probably several thousand light years across. E. Sometimes they appear in pairs, due to gravitational lenses formed by intervening galaxies. 35. What observational evidence suggests that the centers of quasars are small, about a fraction of a light year? A. The fact that quasars emit long wavelength radiation B. Photographs of quasars C. They emit radiation over a very wide range of wavelengths. D. The intensity of their radiation fluctuates over periods of months. E. All of the choices are correct. 36. What is the origin of synchrotron radiation in radio galaxies? A. High speed electrons spiraling around the magnetic field lines B. Supernova explosions C. Neutron stars at the center of the radio galaxy D. Hydrogen gas E. Radiation from a massive black hole at the center of the galaxy 37. What is the origin of the lobes often observed on opposite sides of radio galaxies? A. Gas ejected from the core of the galaxy B. High speed electrons colliding with gas surrounding the galaxy C. Hot planetary nebulas surrounding the galaxy D. Black holes orbiting the center E. Material pulled in by gravity 38. Astronomers speculate that most galaxies have a massive black hole at their center. What could be the origin of the suspected black hole? A. First, a supernova explosion formed a black hole, which in time became more massive by accretion. B. The collision of galaxies C. The gravitational attraction drew in stars from the disk. D. The rapid rotation of the galaxy that compressed material to high densities. E. Dark matter at the galactic center

39. Which of the following provides evidence for the existence of dark matter? A. The orbital speeds of stars in galaxies are higher than what can be accounted for by the detectable mass in the galaxy. B. The orbital speeds of galaxies in clusters are higher than what can be accounted for by the detectable mass of the cluster. C. The ability of rich galaxy clusters to prevent their hot gases from expanding. D. All of the choices are correct. E. Only the orbital speeds of galaxies in clusters are higher than what can be accounted for by the detectable mass of the cluster and the ability of rich galaxy clusters to prevent their hot gases from expanding provide evidence. 40. What is the most likely outcome after the collision between two spiral galaxies? A. The destruction of most of their stars B. Enhanced formation of new stars C. Formation of a larger galaxy D. All of the choices are correct. E. Only enhanced formation of new stars and formation of a larger galaxy are correct. Please place all of your answers on the answer sheet provided. XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

Section-2 follows Answer all questions in this section. To get full credit for a question you must show your work and explain your reasoning in detail. Each of the six multi-part question is worth 4 points. This section is worth 24 points total. All answers on the answer sheet. XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX 1. Comet Halley has an orbital period of 75 years and when it enters the inner Solar System, it passes within a few AU of the Sun. A. Determine the average distance of Comet Halley in AU. Kepler’s third law says the square of the period, T, is proportional to the cube of the semi-major axis, a:

. For Earth, T = 1 year and a = 1 AU, so in these units . For Halley we get

. (a is the average distance over the eccentric anomaly.) B. Right now, Comet Halley is just about past the orbit of Neptune, which has an average distance from the sun of about 30 AU. Explain how this is possible given the average distance you found from its orbital period. Although the average distance, a (the semi-major axis), is less than 18 AU from the Sun, Halley’s orbit is highly eccentric, so its aphelion (most distant point in the orbit) is significantly farther away, in fact almost twice as far. 2. HIPPARCOS (an acronym for HIgh Precision PARallax COllecting Satellite was a scientific mission of the European Space Agency (ESA., launched in 1989 and operated between 1989 and 1993. It was the first space experiment devoted to astrometry, the accurate measurement of star positions, distances from us, parallaxes, and proper motions. A. If the measured parallax shift of star A was 0.1 arcsecs and the parallax shift of star B was 0.05 arcsecs, which star was farther away from the Earth, why? The more distant the object, the smaller the parallax angle. So star B is farther. B. What is the distance of the farthest star in parsecs?

If d is the distance in AU and θ is the parallax angle in arcsec, then d = 1

θ.

So star B is 20 parsec from Earth. C. What is the distance of the farthest star in light-years? This is 65.2 light years.

3. There are two optical telescopes operating at the exact same frequency. The first telescope is a 10 m telescope that is planned to be located at the L2 Lagrangian point 1.5 million kilometers past the orbit of the Earth. The second telescope is a 2 m telescope that is planned to be placed on the far side of the moon (average distance to the moon is 380,000 km from the Earth.. A. Which of the two telescopes will have the greater light gathering power (10 m or 2 m)? The 10 m aperture will gather more light. B. Explain your answer to part (A). The amount of light (photons per second) that will enter a telescope is proportional to the area of the aperture, or the square of the diameter. If the 10m telescope were placed on the Earth on top of Mauna Kea in Hawaii at 14000 feet instead of at L2, which telescope NOW has the greater light gathering power, by what factor C.. The 10 m telescope has a __greater___ (greater/smaller. light gathering power ) D.. by a factor of __(10/2)2 = 25___ times. E. Compare your answers to parts C. and D. to your answer to part A.. Explain any differences. There is no difference. The bigger aperture still collects more light than the smaller. Of course, being on Earth, the air will absorb/scatter some of the incident light, but that is wavelength dependent, and a better analysis would require knowing what wavelengths are being measured. 4. There was a great debate concerning the value of the Hubble constant. (NOTE: The presently accepted value of the Hubble constant is 72 km/s/Mpc as listed in your formula sheet.. One party believed the Hubble constant (Ho. was closer to 50 km/s/Mpc and the other party believed the Hubble constant was closer to 100 km/s/Mp C. Assuming you measure a recessional velocity of a galaxy of 10,000 km/s, what is the distance to that galaxy given the two different Hubble constants A. Distance to galaxy using 100 km/s/Mpc = __100___ Mpc (10,000 / 100) B. Distance to galaxy using 50 km/s/Mpc = __200___ Mpc (10,000 / 50) C. How do the different Hubble constants affect the calculated age of the universe? The inverse of the Hubble constant gives us the approximate age of the universe. If we assume

H0 = 72 km/s/Mpc, then

If instead we assume H0 = 100 km/s/Mpc, then the estimated age is only 10 billion years.

5. If you triple the distance between two celestial objects, how does the resultant gravitational force between the two objects compare to the original force? (for example, 2 times, 10 times, 100 times?. A.. The force is __9___ times B. _weaker____ (greater/weaker).. The gravitational force is inversely proportional to square of distance, and 32 = 9 6. Two stars have the same radius but have very different temperatures. The red star has a surface temperature of 3000 K and the blue star has a surface temperature of 15,000 K. By what factor is the blue star more (or less. luminous compared to the red star? (for example, 2 times, 10 times, 100 times?. A. The blue star is __625___ times B. __more___ (more/less) luminous. The power per unit area radiated by a blackbody is proportional to T4 (i.e., the fourth power of the temperature). The blue star is 5 times as hot as the red, and 54 = 625. XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

Section: Section-3 follows Answer all nine questions in this section. Explain in detail to get full credit. Each question is worth 4 points. This section is worth 36 points total. XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX 1. Below are HR diagrams taken of 4 star clusters. Identify the ages of the star cluster from YOUNGEST to OLDEST and describe in detail how you can determine the relative age of each cluster. Use the HR diagram provided at the end of this exam as a guide in your decision making process. [1] Below are HR diagrams taken of 4 star clusters. Identify the ages of the star cluster from YOUNGEST to OLDEST and describe in detail how you can determine the relative age of each cluster. Use the HR diagram provided at the end of this exam as a guide in your decision making process.

From youngest to oldest is A, D, B, then C 1) In A, half of the stars (the higher mass stars) have reached the main sequence, but the other half (the lower mass stars) are still in the evolutionary T-Tauri phase. 2) In D, the highest mass stars are beginning to move off the main sequence, while lower mass stars have still not yet reached the main sequence. 3) In B, all the O stars, having used all their hydrogen, have gone supernova. The main sequence cutoff is apparent at luminosity > 100. 4) In C, we now see many white dwarfs (lower left), and the red giant branch is filling up . Only K & M stars remain on the Main Sequence, with the rest having left.

2. Assume that the four planets listed in the table below are all terrestrial-type worlds, they formed at the same time, they orbit the same star, and each has nearly circular orbits. Which of the four planets should show the most seasonal variations over its orbit? Explain your reasoning. Which of the four planets is the most likely still to be geologically active? Explain your reasoning. Planet Tilt (Deg) Radius (km) Density (g/cm3) Average Distance from Star (AU. A 1.0 1,111 5.90 1.1 B 23.5 4,051 4.25 2.0 C 47.0 6,950 4.52 3.5 D 0.0 3,397 3.10 5.4 Planet C, with a 47 degree tilt, will have the largest seasonal variations. The seasons are governed by the tilt of the rotational axis with respect to the orbital plane. The larger the tilt, the greater the seasonal variations through the planet’s year. Planet C is also the most likely to be geologically active. This is because geologic activity is principally driven by internal heat, and larger planets will have hotter cores from their greater gravitational compression. 3. Below are images of two moons in the outer solar system. Describe in detail which moon has the younger surface and WHY. [3] Below are images of two moons in the outer solar system. Describe in detail which moon has the younger surface and WHY.

A (left) looks like Europa (Jupiter’s icy moon). This surface appears to have undergone recent and repeated resurfacing, making it a relatively young surface. The heavily cratered surface in B (right) is indicative of a much more ancient surface, unchanged since the period of heavy bombardment billions of years ago.

4. The Big Bang theory of Cosmology is accepted by nearly all astronomers. Please list, and describe, three major observations that support this theory. 1) The cosmic microwave background radiation. This pervasive 2.7 K blackbody radiation, observed to be bathing us rather uniformly in every direction, has the spectral and spatial characteristics precisely as predicted by the Big Bang theory. 2) The oserved redshift of distant galaxies, and the Hubble constant, are consistent with and point to a Big Bang that happened approximately 10-15 billion years ago. 3) The observed amount of heavier elements in the universe, relative to the amount of hydrogen, is as predicted by the Big Bang theory. 5. What is the what attribute of the planets of the outer solar system made them grow so much larger than the Terrestrial Planets? The gas giants formed beyond the “frost line”, beyond which the temperatures are cold enough for light hydrogen compounds like water and methane to condense. Inside the frost line, these light compounds were vaporized, and therefore not incorporated into these inner planets that would become the Terrestrial planets. But, outside the frost line, these light compounds were available and accreted into the large and much lower-density gas giant planets. 6. Why is Europa, a moon of Jupiter considered a prime candidate for finding extraterrestrial life, what are the conditions that allow this? Europa has a very smooth surface lacking craters. This surface indicates the possibility of a subsurface liquid ocean, heated by plate tectonics and tidal forces. Such conditions are not unlike conditions in some places on Earth that do support life. 7. Describe one topic in this course that you found particularly interesting and why (do not use what you led discussions on). You’ll have to answer this one… 8. If the moon rises at 8:55PM tonight a) at what time will it rise tomorrow, b) Why? The moon will rise tomorrow about an hour later than it did today. This is simply because the Moon is orbiting the Earth in the same direction as it rotates. In one day, the moon will have moved about 1/28th of the way around, taking the Earth slightly less than one hour to get to the same orientation with respect to it.

9. According to the latest cosmological view, what will be the fate of the universe? The Universe appears to be expanding at an increasing rate. Depending on the amount of dark energy and dark matter in the universe, it will either eventually slow and then re-collapse on itself, or continue expanding. Based on current observations, it seems unlikely that the universe will slow and collapse in a Big Crunch, but will instead continue expanding. XXXXXXXXXXXXXXXXXXXXXX END XXXXXXXXXXXXXXXXXXXXXXXXXXX