Topic summary
Spectral classification
Extracted from the Wikipedia article Stellar classification.
Harvard spectral classification
The Harvard system is a one-dimensional classification scheme by the astronomer Annie Jump Cannon, who re-ordered and simplified Draper's alphabetical system (see History). Stars are grouped according to their spectral characteristics by single letters of the alphabet, optionally with numeric subdivisions. Main-sequence stars vary in surface temperature from approximately 2,000 to 50,000 K, whereas more-evolved stars – in particular, newly-formed white dwarfs – can have surface temperatures above 100,000 K. Physically, the classes indicate the temperature of the star's atmosphere and are normally listed from hottest to coldest.