Question

Why does your finger seem to move? How is this related to the parallax of stars?

Answer 1

he easiest way to see parallax is to hold out your finger vertically in front of a background object, a door or wall for example. Shut your right eye and note where on the background object the image of your finger appears. Now open your right eye and close the left one without moving your finger. The image of your finger should appear to have jumped to a different spot on the background wall. It is possible to tell how far away your finger is from your eyes just by measuring the distance between your eyes and the distance that the image appeared to move in degrees of arc.