How do we know how massive a star is?  Or how old it is?  Or how fast it is moving?  How massive is our Milky Way Galaxy?  How old is the Universe?  Most parts of the Universe are too far away to reach in person or even with space probes. To answer these questions we have to rely on messages emitted by the objects we wish to study. These messages are, of course, in the form of light. In this lab we are going to study the light we receive from stars.

The purpose of this lab is to allow you to gain a better understanding of how astronomers determine what astronomical objects are like. An example would be the temperature and density inside a nebula or at the surface of a star. The specific technique you will learn about is called "atomic spectroscopy". You will apply this technique to learn about the physical conditions in various astronomical objects.


  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 window should open at the bottom of your screen with the questions.
  3. Read the questions carefully. Examine the text, diagrams and animations in order to answer the questions. You will also be answering questions based on the hands-on activities in this lab. These activities are described on the problems page.
  4. 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.
  5. 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 4 and re-submit. We will only grade the last form you submit.

    Good Luck!