Star Parallax

Parallax is the apparent shift in an object's position when it is viewed from two different points. If you hold your finger in front of your face and close each eye in turn, your finger seems to move. Astronomers use this effect to measure distances to nearby stars.

Parallax was first used to measure the distance to a star in 1838. Astronomers look at a star from opposite sides of Earth's orbit, and the small shift in its position reveals how far away it is.