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What are Cepheid variables?

Cepheid variable stars are the name for a special type of variable star first discovered in the constellation Cepheus. A variable star's brightness changes over time. In the case of Cepheids, imagine your lungs expanding and contracting as you breathe. Cepheid variable stars "breathe" in the sense that they, too, are expanding and contracting, and this causes their brightness to change in a very regular (astronomers say "periodic") way.

Cepheids are extremely important to astronomers because their periodic changes in brightness can be used to figure out how far away they are. Because Cepheids are intrinsically bright stars, they can be seen far away, and astronomers can use them to determine the distance to very distant galaxies.

Submitted by Henrik Berg (Norway)
(February 10, 1998)

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