Final answer:
Astronomers determine the distances to galaxies using a variety of methods, including the period-luminosity relationship for cepheid variables, standard bulbs such as type la supernovae, and the Tully-Fisher relation which connects the line broadening of 21-cm radiation to the luminosity of spiral galaxies.
Step-by-step explanation:
Astronomers determine the distances to galaxies using a variety of methods, including the period-luminosity relationship for cepheid variables, standard bulbs such as type la supernovae, and the Tully-Fisher relation which connects the line broadening of 21-cm radiation to the luminosity of spiral galaxies.
For example, the period-luminosity relationship for cepheid variables allows astronomers to estimate distances to galaxies by measuring the pulsation period of these stars and relating it to their intrinsic brightness. By comparing the observed brightness to the intrinsic brightness, astronomers can determine the distance to the galaxy.
In addition, the Tully-Fisher relation connects the line broadening of 21-cm radiation emitted by hydrogen gas in spiral galaxies to their luminosity. This relationship can be used to estimate distances to galaxies by measuring the line broadening and relating it to the luminosity. The more luminous the galaxy, the greater the line broadening, which can indicate a larger distance.