Astronomy
How Astronomers Measure Distances Using the Parallax Method
Quick fact
The nearest star, Proxima Centauri, has a parallax angle of only about 0.77 arcseconds—roughly the apparent size of a dime viewed from 4 kilometers away.
Why this is interesting
Hold your thumb at arm's length and close one eye, then switch eyes—your thumb seems to jump against the background. Now imagine doing that with a star and half the Earth's orbit as your arm span. How far can that trick measure?