# Q & A: Radio Telescopes and X Ray Telescopes

Q:
Do people listen to radio telescopes? Do x-ray telescopes see through stars the way x-rays see through people?
- John (age 11)
Illinois
A:

John -

Great question! The thing that you have to understand before you can understand this is waves. If you've ever been to the ocean before (or even to Lake Michigan), you've probably seen water waves before. But that's not quite what I'm talking about. Many of the things that you're used to dealing with are matter. (Matter is a fancy word for stuff.) For example, you're made of matter; your house is made of matter; your dog is made of matter; your car is made of matter; all sorts of things are made of matter.

But instead of thinking about these things, let's think about light. You can't touch it. When it hits you, you don't feel an impact like you would if you were hit by a ball. Instead of thinking about light as matter, it's a lot simpler to think about light as being made up of little waves, moving through the air. If you turn on a flashlight in a dark room, it sends out lots (and I do mean /lots/) of little things called photons. Photons are way smaller than you can imagine, and they move really really really fast. These photons move in waves. They bounce off of the things in the room, and some of them come back to your eyes. Then your eyes and your brain translate them into something you can understand.

I know, you asked about radio telescopes, and all I'm talking about is light waves. I'm getting there, trust me! The thing is that radio, X rays, and light are all waves. In fact, they're even the same kind of waves! They're all made up of photons. The only difference is in how long the waves are. Here's a picture to help this make sense:

(from )

Visible light (the colors we see) is made up of waves that have wavelengths (the distance between the tips of the waves) of anywhere between 400nm and 700nm (between 0.0000004 and 0.0000007 meters). Different types of X rays have wavelengths of between 1pm and 10nm (between 0.000000000001 and 0.00000001 meters). And different types of radio waves have wavelengths between 100um and 10m (between 0.0001 and 10 meters). Ok, so that's a lot of zeros, and you don't have to remember all of that. The important part to remember is that X rays have waves that are a lot shorter than the light we see, and radio waves are a lot longer than the waves in the light we see.

So what does this have to do with telescopes? Well, regular telescopes work by looking at visible light waves that come from distant stars. Radio telescopes and X ray telescopes work the same way. Only, instead of picking up visible light waves, they pick up the really short waves or the really long ones that are the radio waves or the X ray waves. But since we can't see these waves with our eyes, the radio or X ray telescopes have computers that make pictures that we /can/ see, using different colors of ink to represent the different wavelengths of the radio waves or the X rays.

The difference between this and the radio in your alarm clock actually isn't very big. Radios pick up the same sort of radio waves, except that they pick up radio waves that come from a lot closer than the telescopes do. Then, instead of having a little computer to change them into a picture, they change them into sound that you can hear, which comes out of the speakers.

X ray machines at your doctor's office also use X rays, but they don't use them quite the same way that the telescopes do. The X ray machine actually produces X rays and shines them through a person's body. These X rays will bounce off of the different things in your body differently. Some of them come back to the camera, which takes a picture. Only it's an X ray picture instead of one that uses visible light. Then, when the pictures are developed, they come out in black and white colors on the film, so that the doctor can see them.

The important thing to understand is that both radios and radio telescopes use radio waves, but they use them in different ways. Similarly, X ray machines and X ray telescopes both use X rays...they just use them differently. If you want to see some pictures taken by radio telescopes, check out this link to an article on the world's most complex radio telescope. For some really cool pictures from an X-Ray telescope, have a look at the website for the telescope at https://chandra.harvard.edu/.

-Tamara

(published on 10/22/2007)