Star classification is a system used by astronomers to categorize stars based on their temperature, color, and spectral characteristics. The most common classification system is the Harvard classification, which uses letters O, B, A, F, G, K, and M to represent different temperature ranges, from the hottest (O) to the coolest (M). Each class can be further divided into subclasses using numbers. In addition to temperature, stars are also classified by their luminosity, which indicates how bright they are. This classification helps scientists understand the life cycle of stars, their chemical composition, and their potential for hosting exoplanets.