Star classification

Class Temperature Apparent color Mass
(solar masses)
(solar radii)
Luminosity (solar luminosity) Approximate main-sequence life span (years) Hydrogen lines  % of all Main Sequence Stars
O 30,00060,000 K blue 64 16 1,400,000 ~10 million Weak ~0.00003%
B 10,00030,000 K blue white 18 7 20,000 ~100 million Medium 0.13%
A 7,50010,000 K white 3.1 2 40 ~1 billion Strong 0.6%
F 6,0007,500 K white 1.7 1.4 6 ~5 billion Medium 3%
G 5,0006,000 K yellowish white 1.1 1.1 1.2 ~10 billion Weak 7.6%
K 3,5005,000 K yellow orange 0.8 0.9 0.4 ~50 billion Very weak 12.1%
M 2,0003,500 K orange red 0.4 0.5 0.04 ~100 billion Very weak 76.45%

Luminosity classes

Symbol Class of Star Example
I Supergiants Betelgeuse, Antares
II Bright giants Canopus
III Giants Aldebaran
IV Subgiants Procyon
V Main sequence Sun, Sirius A
wd or D White dwarfs Sirius B


Hertzsprung-Russel (HR) diagram

Star size


Stellar Lifetimes


Summary of stellar properties

Property How it is determined
Brightness directly measured
Color -Compare brightness in two different E&M spectrum bands.
-Examine spectra of star
Temperature Use color or spectra
Distance -Directly measured via parallax
-Indirectly measured via method of standard candles
Luminosity -use brightness and distance
-Eclipsing Binary: Use Temperature and Size
Radial Velocity Doppler shift of spectral lines
Transverse Velocity proper motion and distance
Rate of Spin Doppler broadening of Spectral Lines
Size -Luminosity and Temperature
-directly measure in an Eclipsing Binary
Mass -Use Kepler's 3rd Law in Binary System.
-Infer from Luminosity and Temperature.
-Infer from spectral lines.
Chemical Composition Spectral Lines
Strength of Magnetic Field Spectral Lines
Age Main-Sequence Turn-off Point in a cluster



Return to class notes TOC.

Page last modified: