What are Star Classifications
Have you ever wondered about star classifications ? Stars are classified based on their temperature, but started out being based on only their spectra. This classification process started in the 1890s by Edward Pickering at Harvard and was finished in 1901 by Annie Cannon, who worked for Pickering. Cannon reorganized what Pickering started in the classification that we know today. The classification is as follows “O B A F G K M” that goes from the hottest stars to the coolest stars. These classifications are further subdivided in categories “0-9” where 0 refers to early in that star and 9 refers to a late type of star.
This classification is now called the Harvard Spectral Classification. Type O stars and Type B stars are both blue-white hot stars, but Type O stars are the hottest stars. Type A stars are white stars that give off Balmer absorption lines in early A stars. Type F stars are yellow-white stars. Type G stars are yellow stars like our Sun. Type K stars are cool orange stars, whose spectra is dominated by metal absorption lines. Type M stars are cool red stars, whose spectra is full of molecular absorption lines. The Sun is classified as a Type G2 star with a surface temperature of 5777 Kelvin. These spectral classes also relate to the surface temperatures of the stars.
The Hertzsprung-Russell Diagram
Class of Star Type of Star Ia Luminous supergiants Ib Less luminous supergiants II Bright giants III Giants IV Subgiants V Main-sequence VI Subdwarfs D White dwarfs
Life Cycles of Stars