Spring 2003 ASTR 1120-002 Midterm Review

Fall 2003 ASTR 1120-002 Midterm Review

The midterm will contain 20 multiple choice questions, each worth 1 point, plus 5 short answer questions each worth 3 points, for a total of 35 points.

The midterm will test everything covered during the semester so far. This means Chapters 1 to 7 of the Hypertex, plus sections 1, 2 and 3 of Falling into a Black Hole (1. Approaching the Black Hole, 2. Orbiting the Black Hole, and 3. Falling to the Singularity of the Black Hole).

Two of the multiple choice questions relate to Falling into a Black Hole. The remaining 18 multiple choice questions relate to the hypertext, and are approximately evenly distributed over the 7 chapters.

There is a marked tendency for questions to be on topics that we specifically emphasized and discussed during the Monday lecture or the Friday discussion session. A small number of the questions are almost verbatim versions of concept questions posed in class. Some others are variations on weekly questions.

The short answer questions are intended to test your understanding of core topics in this course, such as: Give an account of the evolution of a 1 solar mass star.

Review Questions

Distances in Astronomy. Name two measures of distance commonly used by astronomers. What do these measures signify? Describe how trigonometric parallax works.
Looking back. When we look deeper into space, we are looking back further in time. Explain. Be quantitative.
The Nature of Light. What is light? Is it a force? A form of electricity? A form of energy? What has light got to do with electricity and magnetism? Is light a particle or a wave? When does light behave like a wave, and when does it behave like a particle? What phenomena show that light is a wave? What phenomena show that light is a particle? What quantitative properties does light have? How are these quantitative properties related?
Types of Light. Radio waves are a kind of `light'. What other kinds of `light' are there, and in what respects do they differ from each other? What kinds of light can you see? What kinds of light can you feel? What kinds of light can you hear? What kinds of light penetrate the Earth's atmosphere?
Spectrum. What does spectrum mean? What is the difference between emission lines and absorption lines? Draw pictures illustrating setups which might allow you to observe (a) emission lines, and (b) absorption lines from a substance.
Planck or Blackbody Spectrum. What is a Planck, or blackbody, spectrum? Under what circumstances would you expect something to have a Planck spectrum? How is the spectrum related to temperature? What is Wien's Law? How is the spectrum related to color? Is a red star hotter than a blue star or vice versa?
Energy levels of atoms. Why can electrons occupy only orbits with certain specific energies? Draw processes corresponding to (a) emission, (b) absorption, (c) ionization, (d) recombination. How are the energies of emitted/absorbed photons related to the energy levels of atoms? How is photon energy related to frequency? Are the wavelengths/frequencies of emission lines the same as absorption lines? How is the frequency related to the energy levels of the emitting/absorbing atom?
Doppler effect. What is the Doppler effect? What is a redshift? Blueshift?
Absolute Temperature. What is absolute temperature? What is absolute zero? When can an object be described by a temperature? What is thermodynamic equilibrium? What is the spectrum of an object in thermodynamic equilibrium called? What is Wien's Law? What is the Stefan-Boltzmann Law?
Telescopes. Who first used a telescope in astronomy? What factors are important in building a powerful telescope? What is the largest telescope in the world?
Telescopes in space. What kinds of light must be observed from above the Earth's atmosphere?
Plasma. What is a plasma? Under what conditions does matter become a plasma?
Eddington. What profound new idea did Eddington have about the condition of matter inside the Sun that revolutionized our concept of the Sun? How did Eddington estimate the temperature at the center of the Sun? For a description of his ideas in his own words, read Eddington's 1920 Address.
Hydrostatic Equilibrium. What is hydrostatic equilibrium? Is the Sun in hydrostatic equilibrium? Explain.
Solar Energy. What is the source of the Sun's energy? Back at the beginning of the 20th century, a leading theory was Kelvin's suggestion that the Sun was powered by its own gravitational contraction? What was wrong with that theory? Has the Sun ever been powered by gravitational contraction?
Nuclear Fusion. Give an account of the fusion of hydrogen to helium in the Sun. Where does the energy come from?
Energy Transport. By what two mechanisms is radiation transported from the center of the Sun to the photosphere? Give examples where each of these mechanisms occur in everyday life.
Helioseismology. What is helioseismology? What do astronomers learn from helioseismology? To find out more, visit the superb Helio- and Asteroseismology site at the Institute for Physics and Astronomy, Aarhus University, Denmark.
Solar neutrinos. What are neutrinos? By what mechanism does the Sun produce neutrinos? What is the solar neutrino problem? What is the solution of the solar neutrino problem?
Solar Spectrum. Describe the Sun's spectrum. What are Fraunhofer (1814) lines? Explain why the Sun's spectrum looks the way it does. What is it possible to learn from the spectrum of the Sun?
Stellar magnitudes. What is the system of stellar magnitudes? What is the difference between apparent and absolute magnitude?
Stellar Spectra. What are Henry Draper, Annie Jump Cannon, and Cecilia Payne-Gaposchkin famous for? What is spectral type? What has temperature got to do with spectral type? What is the sequence of spectral types?
Hertzsprung-Russell diagram. The Hertzsprung-Russell diagram was the observational key that unlocked our understanding of the stars at the beginning of the 20th century. You should have a thorough understanding of what an HR diagram is, where stars appear in it, and how they evolve in it. Don't forget Stefan-Boltzmann.
Star Clusters. Why are star clusters useful in studies of the HR diagram? The HR diagrams of different star clusters often look very different. Why? Describe the differences.
So Simple a Thing as a Star. The structure and evolution of stars is simpler to understand scientifically than, for example, human beings. Why?
Stellar properties. How do astronomers determine the radius of a star? The mass of a star?
Main sequence. What is the main sequence? What is it a sequence of?
Minimum, maximum mass of a star. What are the minimum and maximum masses of stars? What processes limit the possible range of masses of stars?
Stellar evolution. Give an account of the evolution (a) of a star like the Sun, and (b) of a massive star (greater than about 8 solar masses). Draw the evolution of these stars on an HR diagram, and label the chief events in their lives.
Gravitational Energy. At the beginning of this course we discussed the great principle that when a gravitating system loses energy, it heats up, and we mentioned one example ž how a protostar gets hot enough to ignite hydrogen. We have now encountered several other examples. What are they, and what happens specifically in each case? For example, what role does gravitational energy play: (a) when a main sequence star exhausts hydrogen at its core? (b) when a core collapse supernova occurs? (c) in heating the material in an accretion disk up to x-ray emitting temperatures as it swirls on to a neutron star or black hole?
Quantum Mechanics. According to quantum mechanics, all particles are also waves, with a wavelength inversely proportional to their momentum, and a frequency proportional to their energy. Particles also have spin, a bit like a gyroscope, so they know about direction in space. Particles such as electrons satisfy an `exclusion principle': two electrons cannot occupy the same place simultaneously.
Electron Degeneracy. Electron degeneracy is a quantum mechanical effect that arises because electrons are waves, and they do not like to be packed closer than one wavelength. The fact that the outer electrons of solid metals are electron degenerate is what gives metals their characteristic metallic properties of high conductivity and reflectivity. Electron degeneracy provides the pressure support for white dwarfs and the cores of red giant stars (for stars less massive than about 3 suns). Electron degeneracy plays a crucial role in the Helium flash, and in supernovae of both Types. How does electron degeneracy solve Eddington's paradox: `If a star always grows hotter when it loses energy, how can it ever cool down?'
Explosive nuclear burning. If nuclear burning begins in an electron degenerate plasma, the temperature increases, but the pressure does not (or at least not much). Why does this mean that nuclear burning in an electron degenerate plasma is potentially explosive? Why doesn't the Sun explode like a nuclear bomb? Why is the nuclear burning explosive in (a) a helium flash, (b) novae, (c) x-ray bursters, (d) thermonuclear supernovae?
Helium flash. What is the Helium flash? When does it happen? What happens? Why does it occur? What does helium-burning produce that is crucial to the existence of life?
Red Giant. What is a red giant? What is it made of? What is happening at its center? Red giants typically have strong stellar winds; what does the wind do to the red giant? Are red giants necessarily more massive than main sequence stars? Are they necessarily older? Are they necessarily larger? Are they necessarily cooler?
White Dwarf. What is a white dwarf? What is the observational evidence for their existence? What pressure holds it up against gravity? What happens as the mass of a white dwarf increases, say because a binary companion is losing material on to the white dwarf?
Planetary Nebula. What is a planetary nebula? What is the connection between a red giant, a planetary nebula, and a white dwarf?
Chandrasekhar Limit. What is the Chandrasekhar Limit? What role does the Chandrasekhar Limit play in each of the two types of Supernova?
Nova, X-Ray Burster. Compare and contrast a nova and an x-ray burster.
Thermonuclear supernova. What observational evidence suggests that thermonuclear supernovae represent the explosion of a white dwarf? Why does the light curve (the brightness of the supernova as it changes with time) suggest that the light is powered by the radioactive decay of Nickel 56? What causes the white dwarf to explode? What is the source of the energy of the explosion? Does the supernova leave behind any part of the star?
Core-collapse supernova. What observational evidence suggests that core-collapse supernovae represent the explosion of massive stars? Describe the sequence of events inside a star more massive than about 8 solar masses which is thought to lead up to a supernova. What powers the explosion? The core of the star is made of iron just before it collapses. Why iron? What stops the collapse of the core? The electrons and protons of the iron core combine into neutrons, emitting in the process what kind of particle? What is the source of the energy of the explosion? Does the supernova leave behind any part of the star?
Neutron Star, Pulsar. What is a neutron star? What is a pulsar? How are they thought to form?
Crab Nebula. What is the Crab nebula? Why do astronomers think that it is the remnant of a supernova observed in 1054? Give an account of the essential role that the Crab nebula played in clarifying the nature of pulsars.
Gamma Ray Burst. What is a gamma ray burst? What evidence suggests that the objects producing gamma ray bursts are a cosmological distances? What are the leading theories for gamma ray bursts?
Black Hole. What is a black hole? What is it made of?
Schwarzschild Radius. How do you spell Schwarzschild? What is the significance of the Schwarzschild radius? What is the horizon of a black hole? What happens to time near the Schwarzschild radius (a) as observed by an outside observer, (b) as observed by someone actually there, near the Schwarzschild radius?
Friend falls into a Black Hole. You watch a friend fall into a black hole. Describe what you see. See orbit.
You fall into a Black Hole. You fall into a black hole. Describe what you see and experience. See singularity.
X-Ray Binaries. What is an x-ray binary? What is an accretion disk? What produces the x-rays? What heats the material to the point where it emits x-rays? What evidence might suggest that the compact object in an x-ray binary is a neutron star or black hole?
Observational evidence for Black Holes. If black holes are black, how can you tell if one is there? What is the evidence which suggests that Cygnus X-1 contains a black hole?

Updated 2003 Mar 3