Wilson–Bappu effect

The Wilson–Bappu effect is an astronomical phenomenon observed in the field of stellar spectroscopy, particularly concerning the stars designated as Cepheid variables. It describes a correlation between the period of pulsation of Cepheid variables and their mean luminosity (brightness). Essentially, this means that the longer the period of pulsation of a Cepheid variable star, the more luminous it is. This relationship is crucial for distance measurement in astronomy.