Star Classification Table

A Stellar Classification carries three alpha-numeric characteristics that give details on the luminosity, surface temperature, and size of the star. The three characters are a letter, a number, and a roman numeral. The letter represents the spectral class of the star and goes from bluest to reddest: O,B,A,F,G,K,M. These spectral classes are subdivided by temperature by the number from 0 (hottest) to 9 (coolest). Lastly a roman numeral indicates the luminosity class, also known as the evolution stage. 0 or 1a represent Hyper-giants, I represents Super-giants,II represent Bright Giants, III represents standard giants, IV represent Sub-giants, V represent Main Sequence Stars, and VI represent white dwarf stars.

=Luminosity Class=

VI: White Dwarves
These are extremely small, extremely dense stars. These are the remains of a star up to approximately three solar masses in size after they have exhausted all of their nuclear fuel. These stars are supported by electron degeneracy pressure, have the mass of the sun, and the size of the Earth.

V: Main Sequence
These Stars are the standard stars in terms of stability and system forming. Stars are classified as Main Sequence during the totality of their Hydrogen burning period. Sol is a G2V type main sequence star, as are most stars with life.

IV: Sub Giants
Sub-Giant Stars are the late evolution phase of low mass stars after they begin burning out their hydrogen fuel. As they do this they begin shell-burning Hydrogen causing them to puff up to much larger size but a much cooler surface temperature causing them to drop in their Spectral Class. Sub-Giants that begin Helium Fusion can increase their spectral types back up to around their Main Sequence levels.

Sub-Giants will eventually result in Planetary Nebulae and a White Dwarf Star.

III: Giants
Mid-range mass stars will become Giants after their Hydrogen fuel runs out. These stars are usually able to burn Helium sooner after running out of Hydrogen due to the increased mass and thus don't often drift as low in their spectral types, but some can. Giants can also be formed from some lower mass stars entering what is known as an Asymptotic Giant Branch of extreme pulsation where they will loose their outer shells resulting in Planetary Nebulae.

Most Giants will eventually result in Planetary Nebulae and a White Dwarf Star.

II: Bright Giants
Bright Giants are slightly bigger and much brighter than Giants because they come from higher mass stars that have begun multiple levels of shell burning. These extremely bright giants will often go through several different phases of core burning before eventually going supernova and resulting in a neutron star.

I: Super Giants
Super Giants are formed by the Higher mass stars as they move off of the main sequence. There is a broad range of Luminosities, and temperatures in the Super-giant branch due to the multiple levels of burning that can take place in these larger stars. These stars are all massive enough that they will eventually supernova and leave behind a neutron star or a black hole.

0/Ia: Hyper Giants
Hyper Giant Stars are formed by the highest mass stars and can be extremely variable in their temperature and luminosity. These stars will supernova and create a black hole, though some of the more massive of these stars have been known to explode with energies dwarfing those of traditional supernovae and are known as hypernove.

=Spectral Types=

CLASS O
Class O stars are extremely hot and luminous. The majority of the light emitted by these stars is in the mid to upper UV range. Only 1 in 3,000,000 stars is a type O star. Because Type O stars are so massive they tend to be the first type of star to form when a nebula begins to fragment and collapse, and because they're so hot and luminous they burn through their fuel extremely quickly and have the shortest life-span in all stages of the evolution cycle. Most Type O stars, go through protostar, main sequence, giant, and supernova before a typical type G star even begins burning it's Hydrogen fuel.

TEMPERATURE - 28,000 - 50,000°K SPECTRUM - Ionized atoms, especially helium EXAMPLE - Mintaka (01-3III)

CLASS B
Class B stars are the second most luminous types of stars. Their spectra tend to peak in the Violet and Upper Blue areas. Around 1 in 800 stars is a type B star. Type B stars are also very short lived (only slightly longer than a type O) and tend to be found in what are known as OB associations, regions of active star formation where lower mass stars are still in the process of forming while the O and B Types are well into their main sequence.

TEMPERATURE - 10,000 - 28,000°K SPECTRUM - Neutral helium, some hydrogen EXAMPLE - Alpha Eridani A (B3V-IV)

CLASS A
Class A stars are the third most luminous and are one of the more common naked-eye viewing stars. Around 1 in 160 stars is a type A, and these stars tend to peak in the blue looking blue-white. These stars are much longer lived than B Type, usually beginning their Main Sequence life around the end of the type O stars and existing well past the B-Types.

TEMPERATURE - 7,500 - 10,000°K SPECTRUM - Strong hydrogen, some ionized metals EXAMPLE - Sirius A (A0-1V)

CLASS F
Class F stars are less massive than A type stars and make up roughly 1 of every 33 stars. They are one of the most common naked-eye viewing stars, and their spectrum peak in the middle of the visible spectrum giving them a white appearance.

TEMPERATURE - 6,000 - 7,500°K SPECTRUM - Hydrogen and ionized metals, calcium and iron EXAMPLE - Procyon A (F5V-IV)

CLASS G
Class G Stars are one of the most common stellar types to support life-bearing planets. This is due to their moderate radiation, providing ample energy, but no lethal levels, as well as their long life spans allowing for the development of complex life. 1 out of every 14 stars is a type G. These stars usually peak in the Yellow-to-Green spectrum.

TEMPERATURE - 5,000 - 6,000°K SPECTRUM - Ionized Calcium, both neutral and ionized metals EXAMPLE - Sol (G2V)

CLASS K
Class K stars are much lower mass than the others with an overall orangeish color. 1 in 8 stars is a class K and like class G there is a very high probability of these stars developing life on the plants that form around them.

TEMPERATURE - 3,000 - 5,000°K SPECTRUM - Neutral Metals EXAMPLE - Alpha Centauri (K0-3V)

CLASS M
These are the coolest and dimmest stars with a spectrum peaking in the Red to UV. These are also the most common stars with 3 out of every 4 stars being Class M.

TEMPERATURE - 2,500 - 3,500°K SPECTRUM - Ionized atoms, especially helium EXAMPLE - Wolf 359 (M5-8V)