Luminous galaxies are bright galaxies that emit a significant amount of light, primarily due to the presence of numerous stars and active star formation. These galaxies can be observed across vast distances in the universe, making them important for studying cosmic evolution. Examples of luminous galaxies include spiral galaxies like the Milky Way and elliptical galaxies that contain older stars. The brightness of luminous galaxies is often measured in terms of their luminosity, which is the total amount of energy they radiate per second. This characteristic helps astronomers classify galaxies and understand their structure and composition. Luminous galaxies can also host active galactic nuclei (AGN), which are regions at their centers that emit enormous amounts of energy.