The Hubble classification system is a method used by astronomers to categorize galaxies based on their shapes and structures. Developed by Edwin Hubble in the 1920s, it divides galaxies into three main types: elliptical, spiral, and irregular. Each type has subcategories that further describe their characteristics, such as the tightness of spiral arms or the roundness of elliptical shapes. Elliptical galaxies are smooth and featureless, while spiral galaxies have distinct arms winding around a central bulge. Irregular galaxies lack a defined shape and often appear chaotic. This classification helps scientists understand galaxy formation and evolution in the universe.