Variable stars

Variable stars have been observed since the dawn of human history. The first documented periodic variable was the eclipsing binary Algol. The periodic variable Omicron Ceti, later named Mira, was discovered in the 17th century, followed by Chi Cygni then R Hydrae. By 1786, ten had been documented. Variable star discovery increased rapidly with the advent of photographic plates. When Cepheid variables were shown to have a period-luminosity relationship in 1912, this allowed them to be used for distance measurement. As a result, it was demonstrated that spiral nebulae are galaxies outside the Milky Way. Variable stars now form several standard methods (or rungs) on the cosmic distance ladder that is used to determine the scale of the visible universe. The periods of eclipsing binaries allow for a more precise determination of the mass and radii of their component stars, which is especially useful for modelling stellar evolution.