Variable stars, such as Cepheid variables and RR Lyrae stars, are used in what important measurement in astronomy?

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Variable stars such as Cepheid variables and RR Lyrae stars are used for distance measurement in astronomy. They have a predictable relationship between their luminosity and their period of variability, which allows astronomers to determine their distance from Earth. This is used in many applications, including the measurement of distances to other galaxies and the determination of the expansion rate of the universe.

Variable Stars, Such as Cepheid Variables and RR Lyrae Stars