Follow your curiosity

What discovery has been shared with you?

FACTREE gives you something interesting to discover every day — and something worth talking about together.

Start with one fact. Explore it, go deeper, then follow whichever branch catches your imagination.

Choose subjects for a surprise

Exploring any topic

Begin your discovery

Your next discovery is one click away.

Choose one or more subjects above, or leave Any Topic selected and let curiosity decide.

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?