Final answer:
Astronomers use various techniques like parallaxes, main sequence fitting, cepheids, the Tully-Fisher relation, and supernovae to estimate the distances of galaxies. while type Ia supernovae can be used as standard candles with known peak brightness.
Step-by-step explanation:
The distance ladder is a series of techniques used by astronomers to determine the distances of galaxies. These techniques include parallaxes, main sequence fitting, cepheids, the Tully-Fisher relation, and supernovae. Parallax is the most fundamental method and relies on measuring the apparent shift of a star's position due to Earth's orbit around the Sun.
Main sequence fitting uses the properties of stars on the main sequence to estimate distances. Cepheids are pulsating stars that have a well-known relationship between their pulsation period and their luminosity. The Tully-Fisher relation connects the line broadening of 21-cm radiation to the luminosity of spiral galaxies, while type Ia supernovae can be used as standard candles with known peak brightness.