How do astronomers measure the distances to faraway galaxies?

Astronomers estimate cosmic distances with several methods that work at different ranges. For nearby stars, they use trigonometric parallax, the tiny apparent shift seen as Earth orbits the Sun, a technique refined by missions such as Hipparcos and Gaia. For galaxies beyond the reach of parallax, they rely on standard candles, especially Cepheid variable stars and Type Ia supernovae, whose true brightness is known or can be calibrated. Edwin Hubble used Cepheids in the 1920s to show that the Andromeda “nebula” was a separate galaxy. Today, these methods are cross-checked with redshift and other techniques to build the cosmic distance scale.