A standard candle is an astronomical object that has a known
luminosity Standard candles are the basis for several important
methods of deriving distances in extragalactic astronomy in the
cosmic distance ladder Comparing its known luminosity (or its
derived logarithmic quantity, the absolute magnitude ) and its
observed brightness (apparent magnitude ) the distance to the
object can be calculated as: where D is the distance, kpc is
kiloparsec (103 parsec), m the apparent magnitude and M the
absolute magnitude (both in the same band at rest). (Note that
this is closely related to the distance modulus of an object.)
Standard candles include: - RR Lyrae variables — red giants
typically used for measuring distances within the galaxy and in
nearby globular clusters. - Eclipsing binaries — In the last
decade, measurement of eclipsing binaries' fundamental
parameters has become possible with 8 meter class telescopes.
This makes it feasible to use them as indicators of distance.
Recently, they have been used to give