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.
|The infinite variety of stars|
|Star||Star type||Luminosity class||Absolute magnitude|
|Rigel β Orionis||B8 Ia||Blue-white supergiant||-7.84|
|Sirius α Canis Majoris||A1 v||White, main sequence||+1.42|
|Procyon α Canis Minoris||F5 v||Yellow sub-giant||+2.6|
|Alpha Centauri A||G2 v||Yellow (sun-like)||+4.38|
|Aldebaran α Tauri||K5 III||Orange giant||-0.63|
|Betelgeuse α Orionis||M2 lab||Red supergiant||-6.0|
|Barnard's Star||M5||Red 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.
- Blue Supergiant
- Blue Giant
- Blue Straggler
- White Giant
- Red Hypergiant
- Red Supergiant
- Red Giant
- 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 hypergiant||1 977 million kilometres|
|Red giant||1 376 million kilometres|
|Blue supergiant||110 million kilometres|
|Sun||1 392 000 kilometres|
|White dwarf||13 830 kilometres|
|Neutron star||2 kilometres|
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|
|Class||Effective temperature||Vega-relative chromaticity||Chromaticity|
|B||10 000°C - 30 000°C||Blue-white||Blue|
|A||7 500°C - 10 000°C||White||Deep blue-white|
|F||6 000°C - 7 500°C||Yellow white||White|
|G||5 200°C - 6 000°C||Yellow||Yellowish white|
|K||3 700°C - 5 200°C||Light orange||Pale yellow orange|
|M||2 400°C - 3 700°C||Orange red||Light orange red|
|Source: Harvard Spectral Classification|
By Nigel Benetton, science fiction author of Red Moon Burning and The Wild Sands of Rotar.
Last updated: Saturday, 20 March 2021