Astr 222 Final Exam Study Questions

Short Answer Questions

The final exam will list NINE short answer questions; you must pick SEVEN of them to answer. Roughly half of the questions will cover Cosmology and the other half will cover material from the Milky Way and Galaxies sections of the course. The questions below are examples from the Cosmology section of the course; you should review the study notes for Midterms 1 and 2 for examples from earlier sections.

Each short answer should be a short paragraph or so in length, and they will be worth 5 points each. Remember, feel free to include a sketch in your answer if it helps you explain things.

  1. Describe what was was happening in the Universe at the era of recombination.
  2. Sketch how the expansion factor changes with time (i.e., the R(t) plot) for a Universe with H0=72 km/s/Mpc, OmegaM=2.0, and OmegaL=0.0. Give two reasons we can easily rule this out as the correct set of cosmological parameters.
  3. Explain why matter and dark energy work together to make the Universe spatially flat, but work against each other to change the expansion history of the Universe.
  4. Describe what we mean by hierarchical galaxy formation.
  5. Describe how studies of distant supernovae have helped astronomers better understand the expansion history of the Universe.

Essay Questions

The final exam will have TWO essay questions; you must answer both, and they will be worth 15 points each. One will come from the list below, which concentrates on the Cosmology section of the course. The other will come from the essay questions lists for Midterm 1 and Midterm 2.

Your essays should be ~ 2-3 blue book pages in length; essays much shorter than that probably will not be giving enough detailed explanation to get full credit.
  1. Describe the early history of the Universe, starting with inflation and going through recombination.
  2. Describe (in detail) 3 pieces of evidence for dark matter in the Universe (using evidence that we have discussed in class).
  3. Give plausible values for the cosmological parameters: age, H0, OmegaM, OmegaL. For each, describe two pieces of evidence which supports the value you've given.
  4. Two cosmological processes --- Big Bang Nucleosynthesis and the formation of structure in the Universe --- provide some of our strongest constraints on the nature of dark matter. Describe these two processes and explain how they demonstrate that dark matter cannot be baryonic.
  5. Describe the flatness and smoothness problems, and explain how inflation fixes these problems.
  6. Why does large scale structure in the Universe grow differently under different cosmological models? Describe/explain the difference in how structure forms both between cold and hot dark matter cosmologies, as well as in cold dark matter cosmologies with different values for OmegaM and OmegaL. Explain how can we constrain the value of OmegaM using observations of large scale structure.
  7. Describe how the appearance of a normal spiral galaxy would change (in terms of apparent magnitude, angular size, surface brightness, and morphology) if we were to magically move it to higher and higher redshift and observe it with Hubble. You don't need to give quantitative numbers, but describe qualitatively what is happening. How would things be different if you did the same exercise with an elliptical galaxy instead?
  8. Explain what the microwave background is and how it formed, and explain a few reasons why it is so important for our understanding of the Universe. Why does it have a temperature of roughly 3K? Imagine being a cosmologist roughly 7 billion years ago -- roughly what temperature would you measure for the microwave background at that time? Explain your answer.


There will be THREE calculation problems listed on the final; you must complete all three. Each answer will be worth 5 points. These problems will be similar to the ones listed below.
  1. You are observing a galaxy group consisting of three galaxies. One of them is a spiral galaxy with an apparent I-band magnitude of 12.3 and an inclination-corrected (i.e., true) rotation speed of 220 km/s. How far away is the group? If the other galaxies have apparent I-band magnitudes of 12.5 and 12.0, what is the luminosity (in solar luminosities) of the brightest galaxy? What is the total luminosity of all the galaxies combined?
  2. If you had a telescope that could detect objects down to mB=22, what is the maximum distance a galaxy could be at if you wanted to study its globular clusters (which have a typical luminosity of LB ~ 6x105 Lsun)?
  3. You are studying two galaxies which have both had Type Ia supernovae in them. The supernova in Galaxy 1 had a maximum brightness of mB=12, while the one if Galaxy 2 had a maximum brightness of mB=15.5. How much further is Galaxy 2 than Galaxy 1? You do not need to know the absolute maximum magnitude of supernovae Ia to answer this!
  4. Show how the Friedman equation (given on the equation sheet) can be used to derive the mass density of a flat universe without a cosmological constant. If H0=72 km/s/Mpc, what is the density?