Star Classification Table
Each Spectral class is divided into 10 subclasses, ranging from 0 (hottest) to 9 (coolest). Stars are also divided into six categories according to luminosity: 1a (most luminous supergiants), 1b (less luminous supergiants), II (luminous giants), III (normal giants, IV (subgiants), and V (main sequence and dwarfs). For instance, Sol is classified as a G2V, which means that it is a relatively hot G-classed main sequence star.
CLASS O
DARK BLUE
TEMPERATURE - 28,000 - 50,000°K
COMPOSITION - Ionized atoms, especially helium
EXAMPLE - Mintaka (01-3III)
CLASS B
BLUE
TEMPERATURE - 10,000 - 28,000°K
COMPOSITION - Neutral helium, some hydrogen
EXAMPLE - Alpha Eridani A (B3V-IV)
CLASS A
LIGHT BLUE
TEMPERATURE - 7,500 - 10,000°K
COMPOSITION - Strong hydrogen, some ionized metals
EXAMPLE - Sirius A (A0-1V)
CLASS F
WHITE
TEMPERATURE - 6,000 - 7,500°K
COMPOSITION - Hydrogen and ionized metals, calcium and iron
EXAMPLE - Procyon A (F5V-IV)
CLASS G
YELLOW
TEMPERATURE - 5,000 - 6,000°K
COMPOSITION - Ionized Calcium, both neutral and ionized metals
EXAMPLE - Sol (G2V)
CLASS K
ORANGE
TEMPERATURE - 3,000 - 5,000°K
COMPOSITION - Neutral Metals
EXAMPLE - Alpha Centauri (K0-3V)
CLASS M
RED
TEMPERATURE - 2,500 - 3,500°K
COMPOSITION - Ionized atoms, especially helium
EXAMPLE - Wolf 359 (M5-8V)