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Have you ever looked up at the sky and wondered what you are looking at?  Of course you have seen the stars, but what
exactly is a star?  What else is out there?  And if everything is so far away, how do we even know what is out there?  

The Milky Way

Don't worry, the answers to these question and many more all lie ahead.   

Look at the following picture, what do you see?  What is the difference between the pictures?

Suprisingly, the two images above are of the same galaxy.  You can click on the pictures to learn more about this galaxy, the Coma Cluster.  The image on the left is an optical image.  This is the image you would see with your eyes.  The image on the right is an X-ray image of the Coma Cluster.   Using
images collected from the Chandra X-ray Observatory, we can learn more about this galaxy.  You will learn how we can collect data from the X-ray images.  You will then learn to interpret this data, in a manner similar to an astrophysicist.

To begin, we will learn how to determine the photons' arrival time, the energy, and the position in the sky so you can gain a better understanding of the pictures you will view.

So let's have some fun interpreting some data.

Click here to begin your lesson on interpreting X-ray pictures.

Once you know about the x-ray pictures that you see on the Chandra site you may begin to wonder how far the stars and other gallaxies are from Earth? Which stars and galaxies are closer to us and how can we tell? Does the brightness of the star mean that the star is closer to us?  Can we even answer these questions? If we can, how do we know what we know?

Let’s find out! Go to the section on coordinate systems.

After you finish the sections above, you may want to know the size of the objects in the sky.  But how can we determine this?  How do measure objects when they are so far away?  It is not like we can take out a ruler and measure the object.  First of all the objects are too big and secondly, the objects are too far away.  So how do we know that the  moon is about 2500 miles across?  To find out, go to the section on the size of objects in the sky.

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