Scientists cannot stretch a measuring tape from the Earth to a nearby star, so how do they know how far away they are? Scientists use something called Parallax. Parallax means simply that they look at how much the stars move in the sky back and forth throughout the year as the Earth circles the Sun. This is not something unfamiliar to you. In fact, if you stretch out your hand in front of you and look at your thumb while taking turns covering one eye and then the other, your thumb will appear to move back and forth. Stars do the same thing, but our eyes are much too close to see the difference. However, if we take a picture while on one side of Earth's orbit, and then take another when we get to the opposite side of the orbit, then we have a large enough distance that we can see the stars parallax, and determine how far away they really are. |
