The following two-week lab exercise introduces you to one of the greatest discoveries of modern science - the discovery that the universe is expanding! During week #1 you will use a realistic computer simulation (Project CLEA) to gather spectroscopic data from 13 pre-selected galaxies. From this data you will, by the end of week #2 have prepared a report in which you argue that this data implies that the universe is expanding.

Week One - Collecting and Analyzing

Collecting the Data

  1. Logon to one of the Astronomy Lab (S210) laptops and click on the following icon: Click here to watch a video of how to login to CLEA. (iPhone version) If you would like to install this on your own computer (pc only) follow this link.
  2. Once you have logged in, selected the appropriate exercise - in this case you want the "Hubble Redshift-Distance Relation" exercise.
  3. Next, select the 4.0 m telescope, and once you have acquired the telescope, open the observatory dome. You are almost ready to start collecting data.
  4. Turn on telescope tracking and then go to your first galaxy. Click here to watch a video showing how to select your first galaxy.
  5. You are now ready to acquire your first spectrum. The following video will take you through the steps needed to acquire and save your first spectrum. Make sure that you record both the name of the galaxy and the apparent magnitude of the galaxy at this point! You can begin to fill out the first columns of the attached table.
  6. There are 13 pre-selected galaxies for you to measure. Click on this video to see more on how to acquire and save the rest of the spectra.

Analyzing the Spectra

  1. View the following video clip to see how to measure the position of the K and H lines. You should record your data and eventually summarize in a table similar to the one shown below.
  1. Use the applet HKline to calculate the velocity implied by the red shift in the K and H lines - average these two velocities and record in your data table.
  2. You will also need to determine the distance modulus and distance for each galaxy. These galaxies have all been selected as "standard galaxies" and have an expected absolute magnitude M = -20.1.
  3. Finish filling out the table you downloaded earlier. When done you will have a graph that you can cut and paste into your lab report as well as a value for Hubble's Constant. Be sure to save this file!

Week Two - Interpreting and Writing the Report

You should prepare a formal report in which you present your data and your measured value for Hubble's constant. As important as your data and analysis are your conclusions. You should discuss what Hubble's constant tells us about the universe and in particular what your measured value implies for the age of the universe. Your report should include the following sections and features:

  • separate cover sheet indicating the title of your study (avoid things like Astro 201 Lab #....) - Use a title that indicates something about the science being done (Determining the Hubble Constant or Investigating the Hubble Velocity-Distance Relation, etc.). List your self as principal author but also list contributors (people you worked with).
  • An introduction in which you describe what your report is about, what you will present and what you hope top find.
  • A presentation of the data or observations. This should include your data table (properly labeled) as well as the Velocity-Distance graph (also properly labelled).
  • An analysis section in which you explain how you determined the velocity (this is where you would put any relevant equations - don't say "I used the online calculator" instead say something like, "using the equation.... velocities were determined."
  • A conclusion in which you discuss your results and what they tell you. In this section you should include a discussion of the implied age (Hubble Time) for the universe.