If you look up into the night sky and see a "fuzzy" patch of light it might well be a star cluster. One of the best examples of a cluster is the Pleiades, or Seven Sisters. Formed from giant gas clouds that are compressed by gravitational forces these groups of stars tend to be uniform in in composition and age while varying in size. Clusters allow us to study the evolution of stars all nearly the same age. There are two types, open clusters and globular clusters. The Pleiades has a few hundred stars loosely joined as an open cluster.

In the previous two labs you have studied how to find distances to stars and how astronomers learn about properties of stars. Along the way you learned a little bit about stellar evolution. In this lab you will apply the knowledge you gained in the previous labs toward the study of star clusters. This lab is broken up into two parts. In the first part you will learn how to find distances to star clusters. In the second part you will learn more about stellar evolution by determining ages of star clusters. In the process you will find additional evidence that stars do indeed evolve.


  1. Read the background material by clicking on the topics listed on the menu on the left side of this page. For a given topic there may be multiple pages each of which can be accessed using the navigation buttons arranged across the top of each page.

  2. Click on the menu item "Problems". A question sheet should open at the bottom of your screen. 

  3. Answer the questions on finding distances to star clusters.

  4. Answer the questions on stellar evolution. Use the interactive HR diagram simulator to help you answer the questions.

  5. Answer the questions about the distribution of star clusters in our Galaxy. The interactive cluster plotter will help you do that.

  6. Answer the questions by filling in the form fields on the computer.  Hit the  button labeled "Submit" when you are done. A confirmation page will appear with all your answers imbedded. Be careful not to close the problems window until you are finished and want to submit or your answers may be lost and you will have to reenter your answers.

  7. Check over the confirmation page to make sure that you are happy with your answers. If you need to change your answers go back to step 6 and re-submit. We will only grade the last form you submit.

    Good Luck!