Review Questions for the new topics that will be on the Final Exam Be sure to review the lecture-tutorials and the material we covered on the first three exams. How does speed differ from velocity? Give an example in which you can be traveling at constant speed but not at constant velocity. What do we mean by acceleration? Momentum and Force. What is momentum? How can momentum be affected by a force? What do we mean when we say that momentum will be changed only by a net force? Free-Fall and Weightlessness. What is free-fall, and why does it make you weightless? Briefly describe why astronauts are weightless in the Space Station. Newton's Laws of Motion. State each of Newton's three laws of motion. For each law, give an example of its application. Summarize the Universal Law of Gravitation. What do the different symbols in the equation mean? Be able to use the universal law of gravitation to answer each of the following questions. How does doubling, tripling, quadrupling, etc. the distance between two objects affect the gravitational force between them? How does halving, etc. the distance between two objects affect the gravitational force between them? What is the difference between a bound and unbound orbit? What are possible orbital shapes for objects being effected by gravity? Why do we describe an object that is orbiting the earth to be forever falling towards the earth but never hitting it? What is the law of conservation of energy? What is the law of conservation of momentum? What is the law of conservation of angular momentum? What is the law of conservation of mass-energy? How is related to the formula E = mc 2? Be sure to define each variable. How does this formula explain the generation of energy by the Sun? Where are the proton, neutron and electron found in an atom? What determine an atom s atomic number? Atomic mass number? What is an isotope? A molecule? How do protons (positive charges) and electrons (negative charges) interact? What do me mean when we say that energy levels are quantized in an atom? What circumstances cause electrons to transition between energy levels? Light Transmission. What does it mean for a material to be transparent? To be opaque? Wave Definitions. Define each of the following terms as it applies to waves: wavelength, frequency, cycles per second, hertz, speed. Photon Properties. What is a photon? In what way is a photon like a particle? In what way is it like a wave? What do we mean when we say light is an electromagnetic wave? How is wavelength related to frequency for electromagnetic waves? Kirchoff s Three Laws: Types of Spectra. Summarize the circumstances under which objects produce thermal, emission line, or absorption line spectra.
What does the Stefan-Boltzman law tell us? Wien s law? Doppler Basics. Describe the Doppler effect for light and what we can learn from it. What does it mean to say that radio waves are blueshifted? redshifted? Spectral Summary. Clearly explain how studying an object's spectrum can allow us to determine each of the following properties of the object. a. The object's surface chemical composition. b. The object's surface temperature. c. Whether the object is a thin cloud of gas or something more substantial. d. Whether the object has a hot upper atmosphere. e. The speed at which the object is moving toward or away from us. f. The object's rotation rate. How is a star s apparent brightness related to its Luminosity? How do we measure the distances to the nearest stars? The Inverse Square Law for Light. Using 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. Magnitudes. What is the magnitude system? Briefly explain what we mean by the apparent magnitude and absolute magnitude of a star. What do we mean by a star s spectral type? How is a star s spectral type related to its surface temperature and color? What stars are hottest and coolest in the spectral sequence OBAFGKM? What are the three types of binary star systems? Why are binaries important? What type of binary is studied with a light curve and what can we learn from those studies? 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 luminous? Luminosity Classes. What do we mean by a star's luminosity class? On your sketch of the H R diagram identify the regions for luminosity classes I, III, and V. Stellar Data. Consider the following data table for several bright stars. M v is absolute magnitude, and m v is apparent magnitude. Star M v m v Spectral Type Luminosity Class Aldebaran -0.2 +0.9 K5 III Alpha Centauri A +4.4 0.0 G2 V Antares -4.5 +0.9 M1 I Canopus -3.1-0.7 F0 II Fomalhaut +2.0 +1.2 A3 V Regulus -0.6 +1.4 B7 V Sirius +1.4-1.4 A1 V Spica -3.6 +0.9 B1 V
Answer each of the following questions, including a brief explanation with each answer. a. Which star appears brightest in our sky? b. Which star appears faintest in our sky? c. Which star has the greatest luminosity? d. Which star has the least luminosity? e. Which star has the highest surface temperature? f. Which star has the lowest surface temperature? g. Which star is most similar to the Sun? h. Which star is a red supergiant? i. Which star has the largest radius? j. Which stars have finished burning hydrogen in their cores? k. Among the main-sequence stars listed, which one is the most massive? l. Among the main-sequence stars listed, which one has the longest lifetime? Answers for this question are at the end of the review sheet. What is the defining characteristic of a main-sequence star? What are the differences of high and low mass main sequence stars? Which stars have longer lifetimes? Shorter lifetimes? Why is a star s birth mass its most fundamental property? How do giants and supergiants differ from main sequence stars? What are white-dwarfs? What types of star clusters are there? Why is the study of star clusters important? What is the interstellar medium? What is a molecular cloud? Briefly describe the process by which a protostar and protostellar disk form from gas in a molecular cloud. What is interstellar dust? How does it interact with visible light? What are the consequences for our view of the heavens and how is that view different in infrared light? What causes molecular clouds to contract? Why do stars tend to form in clusters? Describe the process by which a single cloud gives birth to an entire cluster of stars. What is a protostar? How does it form? Why does its mass increase with time? What does it mean when a protostar arrives on the main sequence? What is degeneracy pressure? What is the minimum mass for a star and why can t objects with lower masses be true stars? What is a brown dwarf? What is the maximum mass of a star? Why can t more massive stars remain? How do the numbers of low-mass stars compare with those of higher-mass stars in new star clusters? What equilibrium is the star in when it is on the main sequence? When does a star leave the main sequence? Gravitational Contraction. Briefly describe how gravitational contraction generates energy and when it was important in the Sun's history. Stellar Fusion. What is the overall nuclear fusion reaction in the Sun? Briefly describe the proton-proton chain.
When a star exhausts its core hydrogen fuel, the core contracts but the star as a whole expands? Why? What happens to a low-mass star after it exhausts its core helium? Why can t it fuse carbon into heavier elements? How are Carbon stars important to life? What is a planetary nebula? What happens to the core of a star after a planetary nebula occurs? How does the life of a high-mass star differ from a low-mass star? What is the CNO cycle? How do intermediate stars fit into this picture? Describe some of the nuclear reactions that can occur in high-mass stars after they exhaust their core helium. Why does this continued burning occur in high-mass stars but not low-mass stars. Why can t iron be fused to release energy? What event initiates a supernova? Explain what happens during the explosion and why a neutron star or black hole is left behind. What is electron degeneracy pressure as it relates to the existence of white dwarfs? Describe the mass, size and density of a white dwarf. What is the Chandrasekhar (aka white dwarf) limit? What is a neutron star? A pulsar? Are all neutron stars pulsars? What is neutron degeneracy pressure as it relates to neutron stars? Describe the mass, size and density of a neutron star. Birth of a Black Hole. Briefly explain the process by which the core of a very high mass star can collapse to form a black hole. Event Horizon. What is the event horizon of a black hole? How does it get its name? How is it related to the Schwarzschild radius? What is meant by the singularity of a black hole? Sketch the Galaxy. Draw simple sketches of our galaxy as it would appear face-on and edge-on, identifying the disk, bulge, halo, and spiral arms, and indicate the galaxy s approximate dimensions. Heavy Elements. What do we mean by heavy elements? How much of the Milky Way's gas is in the form of heavy elements? Where are heavy elements made? Chemical Enrichment. Use the idea of chemical enrichment to explain why stars that formed early in the history of the galaxy contain a smaller proportion of heavy elements than stars that formed more recently. Components of Galaxies. Distinguish between the disk component and the spheroidal component of a spiral galaxy. Which component includes the galaxy's spiral arms? Which includes its bulge? Which includes its halo? What is Sgr A*? What evidence suggests that it contains a massive black hole? The Expanding Universe. Recall from Chapter 1 that we know the universe is expanding because (1) all galaxies outside our Local Group are moving away from us and (2) more distant galaxies are moving faster. How do you think Doppler shift measurements allow us to know these two facts? Large Distances. Describe how we can use Hubble's law to determine the distance to a distant galaxy. How odes Hubble s Law lead us to an age estimate of the Universe?
What is dark matter and dark energy? Rotation Curves. Briefly describe how we construct rotation curves for spiral galaxies and how these curves lead us to conclude that spiral galaxies contain dark matter. What are MACHOs and WIMPs? The Big Bang. Explain what we mean by the Big Bang theory. Briefly describe how the cosmic background radiation was discovered. How does the existence and nature of this radiation support the Big Bang Theory? Expanding Universe. What do we mean when we say that the universe is expanding? Why does an expanding universe suggest a beginning in what we call the Big Bang? Answers to Stellar Data Question: a. Sirius appears brightest in our sky because it has the smallest (most negative) apparent magnitude. b. Regulus appears faintest of the stars on the list because it has the largest apparent magnitude. c. Antares has the greatest luminosity of the stars on the list because it has the smallest (most negative) absolute magnitude. d. Alpha Centauri A has the smallest luminosity of the stars on the list because it has the largest absolute magnitude. e. Sirius has the highest surface temperature of the stars on the list because its spectral type, A1, is hotter than any other spectral type on the list. f. Antares has the lowest surface temperature of the stars on the list because its spectral type, M1, is cooler than any other spectral type on the list. g. Alpha Centauri A is most similar to the Sun because it has the same spectral type and luminosity class, G2 V. h. Antares is a red supergiant; its spectral type M means it is red, and its luminosity class I indicates a supergiant. i. Antares has the largest radius because it is the only supergiant on the list. j. Aldebaran, Antares, and Canopus have luminosity classes other than V, which means that they have left the main sequence and are no longer burning hydrogen in their cores. k. Spica is the most massive of the main-sequence stars listed because it has the hottest spectral type of the main-sequence stars; thus, it appears higher on the main sequence of an H-R diagram, where masses are larger. l. Alpha Centauri A, with spectral type G2, is the coolest and therefore the longest-lived mainsequence star in the table.