Morgan-Keenan system

The Morgan-Keenan (MK) system is a standardized way astronomers classify stars based on their spectral characteristics and brightness. It uses spectral types (O, B, A, F, G, K, M) to categorize stars by temperature, from hottest (O) to coolest (M). Each type is subdivided with numbers (0-9), and luminosity classes (Roman numerals I to V) indicate size and brightness, from supergiants (I) to main-sequence stars (V). This system helps astronomers understand star properties, analyze stellar evolution, and compare different stars consistently.