
Method 1: Main Sequence Fitting (finding
distances by comparing main sequence stars of
different clusters).
1. Identify a nearby
cluster with known distance (from parallax), and
thus get the luminosities of its main sequence
stars - standard candle.
2. Take a faraway
cluster's main sequence stars and compare their
brightness to the std. candle.
Since stars of
the same color have the same luminosity, the
difference in their apparent brightness would be
proportional to the distance between
them.
Method 2: Cepheid
Variables
Cepheid stars are very
luminous and
vary in brightness with periods ranging from days
to months. Cepheid variable stars with longer
periods have greater luminosities
(Period-Luminosity Relation).
Because the period
of a Cepheid variable star tells us its luminosity,
we can use these stars as standard candles. Gives
distances up to 100 million
ly.
Method 3: White Dwarf
Supernovae As Standard
Candle
White-dwarf supernovae can also
be used as standard candles, because they happen in
similar stars and hence should have similar
luminosities.
Apparent brightness of white-dwarf
supernova tells us the distance to its galaxy (up
to 10 billion light-years)
Method 4:
Tully-Fisher Relation:
Entire galaxies
can also be used as standard candles galaxy
luminosity is related to rotation speed: as both
are related to mass in the galaxy (higher the mass,
the more luminosity, as well as rotational speed).