Astronomy
The Cosmic Distance Ladder and the Scale of the Universe
Quick fact
The nearest major galaxy, Andromeda, lies about 2.5 million light-years away, yet astronomers gauge that vast distance using pulsating stars called Cepheid variables, which serve as cosmic beacons.
Why this is interesting
You can measure the distance to a galaxy billions of light-years away without ever leaving Earth—but only by climbing a ladder built from starlight.