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Astronomy

The Use of the Tully-Fisher Relation to Measure Galaxy Distances

Quick fact

Brighter spiral galaxies rotate faster, and this simple relationship lets astronomers measure distances to galaxies billions of light-years away with an accuracy of about 10%.

Why this is interesting

You know how you can tell how far away a car is by how bright its headlights appear? Astronomers use a similar trick with entire galaxies—but first they have to figure out the bulb's true wattage.