The two major tools that astronomers have at their disposal for studying the universe are spectroscopy and imaging. Last week you learned about spectra and how they can be used to determine the elements that are found in stars and how they can be used to differentiate between different kinds of stars. This week we will learn about imaging and photometry. Photometry is simply the measurement of the amount of light coming from an object. We will address astronomical photometry in three steps.  We will then look at how we use imaging across the electromagnetic spectrum to learn about the nature of cosmic objects.

In this lab you will learn about how astronomers determine the brightness of an astronomical object such as a star or a galaxy. This is called astronomical photometry and you will use this technique to do some of your own research. Starting with laboratory measurements of the brightnesses of light bulbs you will go on to measure the brightnesses of certain stars and even portions of a galaxy.  You will also learn about how astronomers observe color, and the importance of observing objects over the entire electromagnetic spectrum.


  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 section on measuring the brightnesses of the light bulbs very carefully. Follow the outlined procedure and answer the relevant questions on the problems page.
  4. Read the section on measuring the brightnesses of stars using the interactive photometry simulation. Follow the procedure outlined and answer the relevant questions on the problems page.
  5. Read the section on Multiwavelength Astronomy and answer the relevant questions on the problems page.
  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 7 and re-submit. We will only grade the last form you submit.

    Good Luck!