Astronomy
Mapping the Milky Way's Spiral Structure Using Radio Observations
Quick fact
The 21-centimeter radio wave emitted by neutral hydrogen—the most abundant element in space—passes through dust and reveals the galaxy's spiral arms, something visible light can't do.
Why this is interesting
If you looked at the night sky, you'd never guess the Milky Way is a giant spiral galaxy. So how do we know its shape, when we're stuck inside it?