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©2011 John Sohl, Department of Physics, Weber State University, Ogden, UT 84408-2508 - page 1 / 7





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ASTR/PHYS 1040: Astronomy, Computer Lab The Hubble Redshift-Distance Relation

©2011 John Sohl, Department of Physics, Weber State University, Ogden, UT 84408-2508

Policy overview

You are expected to work on this exercise in groups of one or two. In no case should any group contain three or more people. Do not put this experiment off until the last day. If you have any questions, please come see me, if you wait until the last day and can’t find me, then that’s your problem.

The Task at Hand

You will determine the age of the universe by measuring the distances to several galaxies and the radial velocities of those galaxies.


Near the beginning of the 20th century, astronomer Vesto Slipher noted that the spectral lines of most spiral galaxies were red shifted. He concluded that this was because of the Doppler effect and that these galaxies were all moving away from us.

In the 1920's astronomer Edwin Hubble measured the distances to the galaxies for the first time, and when he plotted these distances against the velocities for each galaxy he noted something very odd: The further a galaxy was from our Milky Way Galaxy, the faster it was moving away, additionally, this was true in all directions. Was there something

special about our place in the universe that made us a center of cosmic repulsion?

Figure 1. The relationship discovered by Edwin Hubble

Astrophysicists were quick to interpret relating the radial velocity of a galaxy to its distance

Hubble’s discovery as a universal expansion of the universe. The distance between all

away from us.

galaxies in the universe was getting larger. Much like the separation between raisins in a loaf of

expanding raisin bread; the very fabric of space, of our universe, is expanding. An observer on any

galaxy would see all other galaxies moving away, and the further away, the faster they move.

Today, we interpret this expansion as the result of a “big bang” which occurred approximately 13.7 billion years ago.

We will reconstruct Hubble’s experiment “using” a remotely operated telescope with a CCD camera and a digital spectrograph. The computer will accurately simulate a viewing and data collecting session for a large remotely operated telescope.


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