In the early twentieth century astronomers thought the Sun was the center of the galaxy. It was not until the astronomer Harlow Shapley that this view changed. Working at Mount Wilson, outside Los Angeles, Shapley studied stars known as RR Lyrae variables. RR Lyraes were interesting because, unlike most stars, their brightness kept changing. Other types of stars also showed this strange variable behavior. Earlier work by Henrietta Levitt on Cepheid variables had shown that there was a direct relationship between the period of the brightness’ variation and the intrinsic brightness of the star. This discovery provided a simple method for calculating the distance to various celestial objects. First, an astronomer would watch a Cepheid