The greatest distance we have dealt with in these labs so far is the distance to the dwarf planet Eris. In terms of light travel time the distance from the Sun to Eris is about 9 light hours. No one really knows how to define the boundary of our Solar System but Eris may be representative of objects in the outermost parts. The next nearest major object is the star Proxima Centauri. In terms of light travel time Proxima Centauri is 4.3 light years away. Think about that a little bit. It takes light 9 hours to get from the Sun to Eris and 4.3 YEARS to get to the Sun's nearest neighbor.

The purpose of this lab is to teach you how astronomers find distances to nearby stars. The specific method we will explore is called parallax. Parallax forms the basis for finding distances to most astronomical objects. You will learn how parallax is used through hands-on activities and you will apply what you have learned to determine distances to some 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.

    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.

    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.
  3. 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!