Cepheids come in two flavours: type I and type II, corresponding to population I and II stars. Population II stars are the
first generation of stars, which formed before the enrichment of the ISM by detritus from earlier stars, and
Population I stars like the Sun are the later generation which contain significant amounts of elements other than
hydrogen and helium. The name “Cepheid” derives from the fact that the star
Cephei was the first to be
identified (by Goodricke in 1784). Population II Cepheids are sometimes known as W Virginis stars, after their
prototype, W Vir, and a W Vir star is typically a factor of 3 fainter than a classical Cepheid of the same
period.