The Variety of Stars

As there are different varieties of nebulae so there are different varieties of stars. Each variety has a distinct lifecycle, and that in turn is determined by its mass at birth. There are over a dozen distinct varieties of stars, though some are theoretical. By far the most popular category are the main sequence stars, which include our own sun and account for about 90% of all stars in the universe.

Omega Centauri star cluster
This colourful assortment of 100 000 stars reside in the massive globular cluster of Omega Centauri. Image credit: NASA, ESA, and the Hubble SM4 ERO Team

The infinite variety of stars
StarStar typeLuminosity classAbsolute magnitude
Rigel β OrionisB8 IaBlue-white supergiant-7.84
Sirius α Canis MajorisA1 vWhite, main sequence+1.42
Procyon α Canis MinorisF5 vYellow sub-giant+2.6
Alpha Centauri AG2 vYellow (sun-like)+4.38
Aldebaran α TauriK5 IIIOrange giant-0.63
Betelgeuse α OrionisM2 labRed supergiant-6.0
Barnard's StarM5Red dwarf+13.4

The  following is a list of all the known types of stars, a few of which are a matter of hypothesis on the part of astronomers. They are briefly described in two sections: Giants and Dwarfs.

The Giants:

  • Blue Supergiant
  • Blue Giant
  • Blue Straggler
  • White Giant
  • Red Hypergiant
  • Red Supergiant
  • Red Giant

The Dwarfs:

  • Yellow Dwarf
  • Orange Dwarf
  • Red Dwarf
  • Blue Dwarf
  • White Dwarf
  • Brown Dwarf
  • Black Dwarf

The next table reveals the typical diameters of some of the star types.

Diameter of star types
Red hypergiant1 977 million kilometres
Red giant1 376 million kilometres
Blue supergiant110 million kilometres
Sun1 392 000 kilometres
White dwarf13 830 kilometres
Neutron star2 kilometres

Spectral classification

First known as the Harvard Stellar Classification the table below was devised by astronomer Annie Jump Cannon (1863 – 1941). She was a contemporary and colleague at Harvard Observatory of Henrietta Leavitt (1868-1921).

The stars are now classified under the Morgan-Keenan (MK) system, using the letters O (the hottest) to M (the coolest). Roughly speaking, O is blue, B is blue-white, A is white, F is yellow-white, G is yellow, K is orange, and M is red. Harvard’s classification agrees until K which it labels “light orange” and M as “light orange red”.

There is a degree of correlation. However, colours can be subjective, especially when you consider they depend as much on temperature as they do on spectral lines, which in turn depend on the relative portion of elements that make up a star. In any event, the human eye is unable to resolve colours at astronomical distances which is why most stars appear white to the naked eye.

Main sequence stars vary in temperature from 2 000°C to 50 000°C. The temperatures are those for the surface of the bodies.

Spectral classification and temperature
ClassEffective temperatureVega-relative chromaticityChromaticity
O>30 000°CBlue
B10 000°C - 30 000°CBlue-whiteBlue
A7 500°C - 10 000°CWhiteDeep blue-white
F6 000°C - 7 500°CYellow whiteWhite
G5 200°C - 6 000°CYellowYellowish white
K3 700°C - 5 200°CLight orangePale yellow orange
M2 400°C - 3 700°COrange redLight orange red
Source: Harvard Spectral Classification

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By Nigel Benetton, science fiction author of Red Moon Burning and The Wild Sands of Rotar.

Last updated: Saturday, 20 March 2021