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Question 1


• Here you will be using Hubble's original sample of galaxies from which he concluded that the Universe was expanding.
  
  Instructions:
  
  USE FIREFOX for this:
  
  
  • open the simulation and select Galaxies Your screen should look like this:
    
    
    
    For this exercise you are only to measure these galaxies:
    
    NGC 2903, NGC 3147, NG 3368, NGC 3627, NGC 5548, NGC 6181, NGC 6764, NGC 7469
    
    For each galaxy you will measure a diameter and a radial velocity (from redshifted spectral lines).
    
    You will then enter those data pairs, X = diameter, Y = velocity, using this plot application
    
    
    • Make sure you select Scatter and not Connected. Enter the data as an X,Y pair and get Plot/Update to see the data.
      
      
    • When your plot is fininshed (i.e. has 8 points on it) then make a screen shot of it and integrate that into your homework document.
      
      
      The screen shot below shows what this application looks like with a couple of fake data points on it
      
      
      
      
    
    
    In the simulation your will measure a diameter and a redshift (velocity). Refer to this tutorial on how to estimate a velocity based on spectral line shifts to longer wavelengths due to motion away from the observer.
    
    For an example, I will go through how to measure the diameter and redshift for one galaxy not on the list. NGCC 6643
    
    AFter I click on NGC 6643 this screen appears:
    
    
    
    which is the REAL spectrum of this REAL Galaxy. Now this galaxy has both emission lines (upward features) and absorption lines, downward features. Its usually easiest to deal with emission lines. The tutorial that you went through tells you that Hβ has an emission line at 4861 Angstroms. For NGC 6643 this line will be measured at a wavelength of 4885 angstroms, or about 25 angstrom shift to the red.
    
    The redshift is then (25/4861) = .005
    
    Multiply that by the speed of light, 300,000 km/s to get a velocity of 0.005 * 300,000 = 1545 km/s (ignore what I say in the video - this is the right velocity).
    
    Now refer to this YouTube Video Tutorial:
    
    
    
    Now that you have done the exercise for all 8 galaxies you are to turn in two things.
    
    
    A. A screen shot of your plot of diameter versus velocity
    
    B. What assumption does Hubble have to make in order to turn this into a velocity-distance relation, from which it can be seen that more distant galaxies are moving at higher radial velocities, than more nearby galaxies.
    
    
    
    
    
  Question 2
  
  
  Summarize the Shapley-Curtis debate and its implications on the overall size of our Galaxy and the size of the Universe. What kinds of evidence did Shapely use to promote his basic premise that our Galaxy was in fact, the entire Universe?

  
  
  Question 3

  Google on "Andrew Mckellar Microwave Background". McKellar actually detected the MWB in (1941!) but did not realize it. Speculate why you think he was unable to put his data together to claim initial discovery and the eventual Nobel Prize for this discovery.