Standard Candle Approach to Distance Measurement

If you know the source strength, or absolute luminosity, of an astronomical object then you can calculate the distance from the observed luminosity using the inverse square law. Many methods are obtained to model the absolute luminosity of particular spectral types of stars and the nature of other objects in the universe. Particularly helpful have been the Cepheid variable stars, whose absolute luminosity is proportional to their period of variability. The Type-1a supernovae have been particularly useful since there is good reason to believe that they all have essentially the same absolute luminosity.