Planetary and Stellar classes

The following information is gathered from various sources, including NASA documents, The original FASA Star Trek RPG, Memory Alpha (where it does not flagrantly disagree with otherwise established classes), and various other sources.

List of known classes

Class	Surface	Atmosphere	Description	Example
A	tenuous, may not be present	reducing; methane, etc.	radiates heat, "failed" star	Jupiter, Saturn
B	tenuous, may not be present	reducing	non-radiant	Neptune
C	iron/silicate	reducing/dense	high surface temperature	Venus
D	nickel-iron/silicate	(A-G)none, (H-N)tenuous	asteroids	Ceres
E	silicate, some metals	reducing/oxidizing	large molten core	Janus IV
F	silicate, some metals	oxidizing	very young	Delta Vega
G	silicate	oxidizing, thin	desert planet	Rigel XII
H	silicate	variable	geologically active	Gothos
I	metallic/silicate	fluid, very dense	small/young	Excalibis
J	silicate	very tenuous, noble gasses	moons	Luna
K	silicate	tenuous, some water	adaptable with pressure domes	Mars
L	silicate/water	oxidizing	geologically inactive	Psi 2000
M	silicate/water	oxidizing	geologically active	Terra
N	water entirely	oxidizing	pelagic planet	Argo
P	water/silicate	oxidizing	glacial planet	Breen
R	water/silicate	negligible	Rogue	Dakala
S	small dense metallic	reducing	small ultra gas giant	Braxis
T	small dense nickel-iron	reducing	large ultra gas giant	Luava
Y	metallic/silicate	reducing	demon class	Silver Blood planet

Stellar Classes

In astronomy, stellar classification is a classification of stars based on their spectral characteristics. The spectral class of a star is a designated class of a star describing the ionization of its chromosphere, what atomic excitations are most prominent in the light, giving an objective measure of the temperature in this chromosphere. Unlike what is the case for planets, stellar bodies are often classed on two scales - size and temperature/color.

Stars based on color and temperature

The following table does include a rough gauge of mass, but this has little to do with the size. Also appended to this is an arabic numeral (0-9), where 0 is among the hottest stars in a class, and 9 is among the coolest.

Class	Surface Temperature	Color	Mass (Solar Masses)	Fraction of All Main Sequence Stars
O	≥ 33,000 K	Blue	≥ 16 M	~0.00003%
B	10,000–33,000 K	Blue/Blue-White	2.1 - 16 M	0.13%
A	7,500–10,000 K	White	1.4 - 2.1 M	0.6%
F	6,000–7,500 K	Yellowish White	1.04 - 1.4 M	3%
G	5,200–6,000 K	Yellow	0.8 - 1.04 M	7.6%
K	3,700–5,200 K	Orange	0.45–0.8 M	12.1%
M	≤ 3,700 K	Red	≤ 0.5 M	76.45%

The following are called "extended classes", which I think will help us when writing as well.

Class	Surface Temperature	Color	Mass (Solar Masses)
L	≤ 2,000	Red/Brown	≤ 0.08 M
T	≤ 1,200	Brown Dwarf	≤ 0.08 M
Y	< 600 K	Brown Dwarf	≤ 0.01 M

Other types of stars do exist, and they may be added here at a later date.

Stars based on size

This scale is based on the radius and luminosity effects of a star. They are generally referred to as "luminosity classes"

Class	Description
0	Hypergiants
I	Supergiants
II	Bright Giants
III	Normal Giants
IV	Subgiants
V	Main Sequence Stars
VI	Subdwarfs
VII	White Dwarfs (Very Rare)

To put things in perspective: Sol is defined as a G2V star. This means it falls into Spectral type G (yellow), is within the hottest 30% of G-type stars (2), and is within the main sequence. To compare, 40 Eridani A (Vulcan's primary sun) is a K1V.