 Distance measures (cosmology)

Distance measures are used in physical cosmology to give a natural notion of the distance between two objects or events in the universe.They are often used to tie some "observable" quantity (such as the luminosity of a distant quasar, the redshift of a distant galaxy, or the angular size of the acoustic peaks in the CMB power spectrum) to another quantity that is not "directly" observable, but is more convenient for calculations (such as the comoving coordinates of the quasar, galaxy, etc.