How do scientists categorize galaxies?

Scientists categorize galaxies based on their shape and structure into three main types: elliptical, spiral, and irregular galaxies. Elliptical galaxies are smooth and featureless, spiral galaxies have distinct arms winding out from a central bulge, and irregular galaxies lack a defined shape. Additionally, galaxies can be classified by their size, brightness, and the presence of active galactic nuclei. This classification helps astronomers understand the formation and evolution of galaxies in the universe.