Flickering Candles: Cepheid Variable Stars

Cepheid variable stars change their intrinsic luminosity in a Cepheid variablespecific manner with periods ranging from days to months. In the early twentieth century, it was found that the intrinsic luminosity of these stars is related to their periodicity thus enabling us to measure distances to stellar clusters and galaxies with confidence. ShapleyShapley, Harlow used this method to construct the first accurate model of our galaxy and the position of the Sun. It was also understood that the change in luminosity is related to a change in the radius of the star. EddingtonEddington, Arthur used the measure of the radius of a Cepheid variable to demolish the hypothesis that the source of the stellar energy is its gravitational contraction. He also proposed a mechanism for the variability, refined by later researchers. Interestingly, the measurement of Hubble’s constantHubble’s constant using Cepheid variables and the Cosmic Microwave BackgroundCosmic Microwave Background do not agree with experimental errors, a fact that has spurred intense activity.