Surface brightness fluctuation

The method measures the variance in a galaxy's light distribution arising from fluctuations in the numbers of and luminosities of individual stars per resolution element.

While the various stars present in a galaxy will cover an enormous range of luminosity, the SBF can be characterized as having an average brightness.

Older elliptical galaxies have fairly consistent stellar populations, thus it closely approximates a standard candle.

Calibration of the method is made empirically from Cepheids or theoretically from stellar population models.

The SBF pattern is evident as the transform of the point spread function in the Fourier domain.