Hold up a finger and look at it with just one eye, then switch to just the other and you'll see your finger appear to ‘jump’ from side to side. The further away the finger, the smaller the jump. This apparent shift of a nearby object against a distant background when observed from different positions is called parallax. Measuring the size of this 'jump' as an angle is the same technique astronomers traditionally used to find the distances to celestial objects such as
