Astronomers Measure Size of a Giant's Sighs

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Science  29 Sep 2000:
Vol. 289, Issue 5488, pp. 2255-2256
DOI: 10.1126/science.289.5488.2255a

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Cepheid variables are giant yellow stars that grow dimmer and brighter over periods of days or weeks. Astronomers have long presumed that the surface layer of a Cepheid variable, called the photosphere, physically expands and contracts to cause this odd behavior. Now, they have caught Zeta Geminorum in the act of swelling and shrinking, making it the first Cepheid that astronomers have actually seen change its size.