Luminosity classes

Luminosity classes are categories used by astronomers to indicate how bright or luminous a star is relative to its size and stage in life. They help differentiate stars of the same temperature but different sizes, such as small, dense main-sequence stars (like our Sun) from larger, more luminous giants or supergiants. The classes range from I (supergiants) through V (main-sequence stars or dwarfs). Essentially, luminosity classes provide context about a star’s size and evolutionary stage, helping astronomers understand its physical properties and life cycle.