Cosmology and Life in the Universe Take Home Exam
Rules: You are on the honor system. Please act honorably. You may not work with others on this exam. All written sources are open to you and you are encouraged to research the answers to these questions as much as possible on your own.
Please type the answers to these questions. Proof read them also. If your answers are not well composed or are confusing, I will deduct points for that. I will not try to figure out what you understand and what you do not. It is up to you to clearly convey what you mean in writing. Each question is worth five points unless stated otherwise.
1. What is Olber’s Paradox? Why is it called a paradox? What does it infer about the universe?
2. Write down Hubble’s Law and explain each of the variables. How does it relate to the age of the Universe? Sketch and label a Hubble diagram. How does one estimate Hubble’s constant from the diagram?
3. Describe how the velocity of a galaxy is measured. Explain each step. Describe how astronomers measure the distance to galaxies using Cepheid variable stars (see your text). Why was the Hubble Space Telescope required in order to see Cepheid variable stars in distant galaxies?
4. Galaxy A is observed to be at a distance of 20 Mpc (Mpc stands for mega parsec) and is receding at a rate of 1400 km/sec. Galaxy B is observed to be at a distance of 30 Mpc and is receding at a rate of 2100 km/sec. Galaxy C is observed to be at a distance of 40 Mpc and receding at a rate of 2800 km/sec. Construct a Hubble diagram and plot the positions of galaxies A, B, and C on it (i.e. make a graph of them). Estimate Hubble’s constant in km/sec per Mpc. Show your work and reasoning. Galaxy D, who lies at a distance of only 1 Mpc is observed to be approaching at 100 km/sec. This measurement is not consistent with the others. Explain why it is inconsistent with the others, and give a possible explanation for the cause of this discrepancy.
5. What do astronomers mean when they say that they think that the Universe is "flat"? List a theoretical (hint: it has to do with inflation) and an observational reason (hint: it has to do with the fluctuations in the cosmic microwave background) why astronomers think that the universe must be flat.
6. List the various components to the total mass-energy density of the universe,Wtotal . Give our best estimates of each term (use the latest estimates from your text). What is dark matter? List three pieces of evidence that we have that it exists. Sketch a curve of the size of the universe vs. time that is consistent with our mass-energy density estimates.
7. Describe how each of the following pieces of evidence strongly supports the Big Bang theory:
A. The existence of the cosmic microwave background radiation.
B. The fluctuations, or structure in the cosmic microwave background radiation.
C. The abundance of helium in the universe.
D. Hubble's law
8. Write down the Drake equation and define each of the terms in it. What is the purpose of the equation?
9. Estimate what each of the terms is and defend your estimates. Estimate the number of advanced civilizations in the Milky Way and comment on your estimate.
10. Estimate the number of planets with life of any kind on them in the Milky Way and comment on your answer. Note - you may disregard all terms that have to do with intelligent and/or civilized life.
Bonus Find the five best pictures that you can of galaxies or galaxy clusters on the internet and print them out. Find out what is significant about each of them and summarize that in a paragraph and include the summaries and pictures with this exam. Up to 10 points total (depends on how great or interesting the pictures are and your explanations). Note if you just provide pictures of the first five that you find, you will likely only receive one or two points for this.