How do we measure the distance to stars and galaxies?

Measuring the distance to stars and galaxies is one of the basic tasks of astronomy. Astronomers use several methods for determining these distances. One common method is parallax, which involves measuring the angle that a star appears to shift against the more distant background stars as the Earth orbits the Sun.

Another method involves using the properties of certain types of stars, such as Cepheids, to estimate their distances. Cepheids are stars that pulse in brightness with a period that is directly related to their luminosity. By measuring the period of the pulsations and comparing it to the observed brightness, astronomers can use the period-luminosity relationship to estimate the star's distance.

For galaxies, astronomers use several methods, including measuring the brightness of certain types of stars and the speeds of the galaxy's stars or gas. One method, called the Tully-Fisher relation, uses the rotational speed of a galaxy's stars to estimate its distance. Other methods involve the brightness of supernovae and the use of standard candles, which are objects with a known brightness and can be used as a reference point for measuring other objects' distances.