by Joseph Long

Previously, I tried explaining adaptive optics in plain English and thought I'd take a stab at high-contrast direct imaging since that's what I work on now. By way of context, there is an xkcd comic that attempts to explain the Saturn V rocket using only the top "ten hundred" most frequently used words in the English language. Trying to follow its example was an interesting challenge in removing jargon from scientific writing.

"Taking pictures of worlds going around other stars"

explained with only the top ten hundred words

The world we live on sits in outer space and goes around our sun. For a long time, we have seen other worlds in the sky that are close by and we are sure that they go around our sun too. But what about other stars? There are many many stars like our own, but we don't know if they all have worlds like ours going around them. We don't know because we haven't checked them all yet! We haven't checked because it is very very hard to take a picture of a world around another star, so we have only looked at some of these many stars to search for worlds. Stars are very bright and any worlds around the star would not be bright at all, and both the star and the world are very far away. That means even a very bright star does not look bright when we see it at night, and a world around that star is very hard to see—if we can see it at all! Because they are far away, we use big mirrors to get as much light as we can from them and use computers to take a picture of how much light there is and keep it for later. If you look at these pictures with your eyes, you only see the star. For a long time we thought this was because there are not many worlds like the ones around our sun. Only in the last tens of years did we figure out that there are worlds hiding around other stars and come up with a way to take pictures of them. When we look for worlds like ours around these stars, almost all of the light we get is from the star and not the world. The star is so bright, we can't even see if there is a world there!

Now we have to explain what we see when we take a picture of a star. In our pictures, the star light does not stay in a tiny point. Almost all of the light goes in a tiny point, but we also see less bright rings around this point. These are not rings like the ones we see around worlds going around our sun. The way we take pictures makes these rings. (This is not something different about the way we take pictures. The way everyone takes pictures of their friends also makes rings like we see, but most of the time we don't notice them because we aren't looking at stars far away.) Because the star is so far away, any picture we take would have the star and any worlds around it very close together. In fact, these rings of light are usually right on top of the light from the other world!

To help us find these worlds more easily, we use pieces of glass that are made to move light from the star out of the way without blocking the light from these far away worlds. That is still not enough to see the worlds in the pictures we take, so we use the picture we keep on our computers to see exactly how much star light is at each point in the picture. Once we know how much star light is in the picture, and where the light is, we can take it off. We do this on a lot of pictures and add them together. When we add them together, it's not as important to know exactly how much light there was in one picture. Think about it this way: on one picture we might be wrong by thinking there is more light when really there is less, but on another picture we think there is less light when there really is more. As long as we are not very far wrong, and we take a lot of pictures, we can add them up and get a really good idea of the way the star light shows up in our pictures.After we take the star light off, any light left is coming from the worlds we are looking for or maybe stuff that is forming into worlds around this star. We take pictures in different colors of light to see if the world is red-hot or cold, and to try and guess what it is made of. We can only use light to do this, since the world is too far away for us to visit. If the world we find has air like our own, we can see colors from whatever is in the air where the star light hits. We can also see if the world is red-hot or cool. We can't say what is inside the world, except by making guesses from what we know about our own world and things we have seen on other worlds around our sun.

We look for worlds around other stars because we want to know if there are worlds like our own. We want to know if we are not alone, and whether life can be found on another far away world. We could learn more about how life comes to be, what kinds of worlds there are, and maybe some day find life like people on a world around another star. That is why people work so hard to take pictures of worlds going around other stars.


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Background image of the Carina nebula by NASA, ESA, N. Smith (University of California, Berkeley), and The Hubble Heritage Team (STScI/AURA)