Astronomy 123: Fourth Homework Assignment


  1. Recent evidence suggests that the Universe is filled with something termed "Dark Energy". What is evidence for the existence of dark energy and what are some hypothesis as to what it is?

  2. Explain how the "top-down" scenario for the formation of structure (e.g. galaxies, clusters of galaxies) in the Universe differs from the "bottom-up" scenario.

  3. Do some research on the concept of "Modified Newtonian Dynamics" or MOND. Discuss the basic idea of MOND and state whether or not you think its a credible alternative to the need for Dark Matter, which we still have not yet detected.

  4. Suppose you were arguing with someone about the Age of the Earth and your foe had an intrinsic distrust of science and its methods and so therefore would not believe anything to do with radioactive age dating.

    Outline what points of "common sense" about the nature of the Earth that you could use to demonstrate that the Earth must be at least millions of years old.

  5. Consider our galaxy to be a very thin circular disk of stars of radius approximately 50,000 light years. If there are currently 2500 civilizations in our galaxy capable of communication, what is the approximate separation of these civilizations (in units of light years) if they are uniformly (e.g. equally spaced) distributed within this circular disk of stars?