Often simply called Cepheids , these variables are massive, high-luminosity stars with short periods of one to 70 days and light variations of 0.1 to 2 magnitudes. Astronomers use Cepheids as a “standard” for distances because of the direct relationship between a Cepheid’s luminosity and variable pulsation period. Once you determine a specific Cepheid’s luminosity and variable pulsation period, you can determine how distant it is because of the inverse square law. This makes Cepheids a major galactic distance indicator.

A graph showing the observations made the variable star AE Ursae Majoris. The X-axis represents time; the Y-Axis apparent magnitude. Note how the star brightens and dims over time, thus the appropriate term variable star. AE Ursae Majoris varies about 0.65 magnitude over a period of 2.2 hours. The brightest phase is called the star’s maximum or maxima; the dimmest is called it minimum, or minima.
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