# What does it mean the number after the stellar class? Magnitude?

What does it mean the number after the stellar class? Magnitude?

Borek
Mentor
Like in G2 for Sun? Subclass. The lower the digit, the colder the star.

Janus
Staff Emeritus
Gold Member
If instead, you mean the roman numeral sometimes placed after the spectral class, this is the luminosity class as follows:

0 Hyper giant
I Super giant
II Bright giant
III Normal giant
IV Sub giant
V Main sequence (dwarf)
VI Sub dwarf
VII White dwarf

Thus the Sun is a G2 V star.

Sub classes of the luminosity class are labled a,ab & b

Great.