Editing Stellar classification (section)

==Stellar classification, habitability, and the search for life==
{{See also|Planetary habitability}}

While humans may eventually be able to [[space colonization|colonize]] any kind of stellar habitat, this section will address the probability of life arising around other stars.

Stability, luminosity, and lifespan are all factors in stellar habitability. Humans know of only one star that hosts life, the G-class Sun, a star with an abundance of heavy elements and low variability in brightness. The [[Solar System]] is also unlike many [[planetary system|stellar systems]] in that it only contains one star (see [[Habitability of binary star systems]]).

Working from these constraints and the problems of having an empirical sample set of only one, the range of stars that are predicted to be able to support life is limited by a few factors. Of the main-sequence star types, stars more massive than 1.5 times that of the Sun (spectral types O, B, and A) age too quickly for advanced life to develop (using Earth as a guideline). On the other extreme, dwarfs of less than half the mass of the Sun (spectral type M) are likely to tidally lock planets within their habitable zone, along with other problems (see [[Habitability of red dwarf systems]]).<ref name="auto">{{Cite web|url=http://www.solstation.com/habitable.htm|title=Stars and Habitable Planets|website=www.solstation.com}}</ref> While there are many problems facing life on red dwarfs, many astronomers continue to model these systems due to their sheer numbers and longevity.

For these reasons NASA's [[Kepler Mission]] is searching for habitable planets at nearby main-sequence stars that are less massive than spectral type A but more massive than type M—making the most probable stars to host life dwarf stars of types F, G, and K.<ref name="auto"/>