“Standard Candles”

A type of object for which we think all objects of that type have the same luminosity
Cepheid Variables (works out to 30 Mpc)
Luminosity of brightest globular cluster around a galaxy.
Luminosity of brightest planetary nebula
Luminosity of Type I supernovae. (Brighter than some galaxies)
All of these methods are based upon the Cepheid calibration!

A type of object for which we think all objects of that type have the same luminosity