Astronomy
How Astronomers Measure Distances Using Parallax
Quick fact
The nearest star system, Alpha Centauri, has a parallax of about 0.75 arcseconds—equivalent to the width of a human hair seen from 2.5 miles away.
Why this is interesting
Hold your finger in front of your nose and close one eye, then the other—it appears to jump. Now imagine doing the same with a star, using the entire Earth's orbit as your eyes.