Each spectral class is further divided into 10 subclasses, ranging from 0 (hottest) to 9 (coolest). Stars are also placed into one of six categories based upon luminosity: 1a (luminous supergiants), 1b (less luminous supergiants), II (luminous giants), III (normal giants), IV (subgiants), and V (main sequence and dwarf stars).

For example, Sol is classified as type G2V. This indicates that is a Spectral Class G star of considerable temperature, and that it is a part of the main sequence.

Spectral Class A

Color: Light Blue
Surface Temp: 7,500 - 10,000 K
Composition: Strong hydrogen and ionized metals
Mass: 3.2 Sols
Radius: 2.5 Sols
Luminosity:80.0
Magnitude: +1
Abundance: 0.63% of stars
Lifetime: 1 billion years
Example: Vega, Sirius

Spectral Class B

Color: Blue
Surface Temp: 10,000 - 28,000 K
Composition: Neutral helium, some hydrogen
Mass: 18 Sols
Radius: 7 Sols
Luminosity: 20,000
Magnitude: -6
Abundance: 0.13 of stars
Lifetime: 100 million years
Example: Rigel, Alpha Eridani

Spectral Class F

Color: White
Surface Temp: 6,000 - 7,500 K
Composition: Hydrogen and ionized metals, calcium and iron
Mass: 1.7 Sols
Radius: 1.3 Sols
Luminosity: 6.0
Magnitude: +3
Abundance: 3.1% of stars
Lifetime: 3 billion year
Example: Canopus, Procyon

Spectral Class G

Color: Yellow
Surface Temp: 5,000 - 6,000 K
Composition: Ionized calcium, neutral and ionized metals
Mass: 1.1 Sols
Radius: 1.1 Sols
Luminosity: 1.2
Magnitude: +5
Abundance: 8% of stars
Lifetime: 10 billion years
Example: Sol, Ka'Tula, Capella

Spectral Class K

Color: Orange
Surface Temp: 3,500 - 5,000 K
Composition: Neutral metals
Mass: 0.8 Sols
Radius: 0.7 Sols
Luminosity: 0.4
Magnitude: +10
Abundance: 13% of stars
Lifetime: 50 billion years
Example: Arcturus, Aldebaran, Alpha Centauri

Spectral Class M

Color: Red
Surface Temp: 2,500 - 3,500 K
Composition: Ionized Atoms, helium
Mass: 0.2 Sols
Radius: 0.3 Sols
Luminosity: 0.04
Magnitude: +15
Abundance: 78% of stars
Lifetime: 200 billion years
Example: Betelgeuse, Proxima Centauri, Wolf 359

Spectral Class O

Color: Dark blue/violet
Surface Temp: 28,000 - 50,000 K
Composition: Ionized atoms, helium
Mass: 60 Sols
Radius: 15 Sols
Luminosity: 1,400,000
Magnitude: -3
Abundance: 0.0000003125% of all stars
Lifetime: 10 million years
Example: Mintaka, Kalidar, Zeta Puppis