Astronomy 123 Second Homework Assignment

Due Friday August 21 by 10 pm

Submit your assignment through Canvas.

Most of these questions will require doing research/reading outside of the course material. That's one of the essential points of homework. Also, there is relevant material available under the resources tab on the course web site.



  1. How did Einstein's new theory help to resolve the dilemma posed by discovering that the orbit of Mercury did not conform to Newton's Laws.


  2. Suppose that I take a spectrum of two galaxies.

    • Galaxy 1 I observe that the hydrogen line has a wavelength of 8204 angstroms.
    • In Galaxy 2 I observe the hydrogen line has a wavelength of 6549 angstroms.


    I know from laboratory measurements that the rest wavelength of this hydrogen line is 6563 angstroms. Given this data, compute the radial velocity of galaxies 1 and 2 using the method described in this tutorial

  3. Google (and don't be lazy and rely on the usually erroneous and incomplete Wikipedia) on "Andrew Mckellar Microwave Background". McKellar actually detected the MWB in 1941 (!) but did not realize it at that time. Speculate why you think he was unable to put his data together to claim initial discovery and hence a future Nobel prize.



  4. Explain why, in a uniformly expanding Universe, every observer would think they are in the center of that expansion.

  5. Explain how the currently observed density of deuterium is a sensitive probe of the baryon density of the early Universe.

  6. Explain why when the theory of inflation first came out in the period 1980 - 1985; that theory demanded that the Universe be completely dark matter dominated.