Star spectral classes

O	White-blue stars, composed by hydrogen, helium, oxygen and other ionized elements. They are very thick and bright and their superficial temperature is about 35.000°K. Example: Alnitak.
B	White-blue stars, composed by hydrogen, helium. They are very thick and bright and their superficial temperature is about 20.000°K. Example: Rigel, Spica.
A	White stars, composed by hydrogen. They are very bright and their superficial temperature goes from 8.000 to 12.000°K. Example: Sirius, Vega, Altair.
F	Yellow-white stars, composed by hydrogen, ionized calcium and potassium. Their superficial temperature is between 6.000 and 8.000°K. Example: Polar Star, Procyon.
G	Yellow stars, composed by hydrogen, helium and several metals. Their superficial temperature is 4.000-6.000°K. Example: Sun, Capella.
K	Orange stars, with presence of calcium and several metals (their spectrum is similar to that of sunspots). Their superficial temperature goes from 3.000 to 5.000°K. Example: Arcturus, Aldebaran.
M	Red stars, characterized by the oxide of titanium. Their superficial temperature is about 2.500°K. Example: Betelgeuse, Antares.
S	Red stars, characterized by the oxide of zirconium. Their superficial temperature is about 2.500°K.
R	Red-orange stars, with presence of carbon compounds. Their superficial temperature is about 2.000°K.
N	Dark red stars, with presence of carbon compounds. Their superficial temperature is about 1.500°K.

Note: each class contains ten subdivisions numbered from 0 to 9.

O