Location of Cepheid variable stars on the HR diagram. Notice Cepheids are luminous stars (up to 104 Lsuns), making them useful for extragalactic distance estamates.
A Cepheid in M100, measured as part of the HST key project.
Period Luminosity relation for Cepheids in various bands. Clearly, the near-IR has less scatter.
Reddening free V I period luminosity relation used for the HST Key Project.