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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.