Here's a fun experiment, one you've probably done already a million times: stick your arm out in front of you. Stick up your left thumb, like you're giving the thumbs up. Close one eye - see where your thumb is? Okay, now switch eyes and close the other one. Did your thumb move? The next step - move your thumb a little closer. Now do it all over again. Did it seem like your thumb was moving even more than before?  What you just did with your thumb is a lot like how scientists measure how far away stars are from Earth. Even though your thumb didn't really move, it appeared to move when you changed which eye was closed. The distance of the apparent movement, caused by a change in which eye you had open, can be measured. In astronomy, the distance of the apparent movement is called a parallax. A parallax is the only direct method that astronmers can use to measure how far stars are that are located beyond our solar system.  What is the closest star to Earth? If you said the sun, you're right. What's the next closest star? I don't know about you but I sure don't have a ruler that long, so we'd need to use parallax. We could stand in the parking lot at Paideia and take a picture of a star with a really special camera. In six months, the Earth will have rotated halfway around the sun, so we would be on the opposite side of our orbit from when we first took the picture. If we take a second picture, we can measure how far the star "moved" in the sky. That apparent movement - the parallax - will tell us how far away the star is. If it moved a LOT, like your thumb did when it was closer to your eye, then the star is close. If it just moved a little, like when your thumb was farther away from your eye, then the star is farther away.  Here's a picture of a parallax that two friends did - one was in the United Kingdom, the other was in Greece. They each marked where they saw the star, compared to the moon, and then showed each other what they saw. Note the distance between the two spots - even though the star never actually moved!