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A '''red dwarf''' is a relatively cool and dim main sequence [[star]] of either spectral class M or late K.  Red dwarfs characteristically are the lowest mass stars in the main sequence, having less then one half of the mass of the [[Sun]], and may have as little as 0.075 times as much (any less and they would not be able to fuse hydrogen and instead becoming [[brown dwarf|brown dwarfs]]).<ref>http://spiff.rit.edu/classes/phys230/lectures/planneb/planneb.html</ref> Their surface temperatures averaging only around 2500 to 3500K. Red dwarfs are actually the most numerous class of stars in the [[galaxy]], making up more than half of all the stars including 21 of the 30 closest stars to our own [[Solar System]].<ref>http://www.daviddarling.info/encyclopedia/S/starsnearest.html</ref>

A '''red dwarf''' is a relatively cool and dim main sequence [[star]] of either spectral class M or late K.  Red dwarfs characteristically are the lowest mass stars in the main sequence, having less then one half of the mass of the [[Sun]], and may have as little as 0.075 times as much (any less and they would not be able to fuse hydrogen and instead becoming [[brown dwarf|brown dwarfs]]).<ref>http://spiff.rit.edu/classes/phys230/lectures/planneb/planneb.html</ref> Their surface temperatures averaging only around 2500 to 3500K. Red dwarfs are actually the most numerous class of stars in the [[galaxy]], making up more than half of all the stars including 21 of the 30 closest stars to our own [[Solar System]].<ref>http://www.daviddarling.info/encyclopedia/S/starsnearest.html</ref>

Despite being the most numerous type of stars in the galaxy, no red dwarf is visible in the night sky by the unaided eye even under the best conditions, including the closet star to us, [[Proxima Centauri]]. Even the largest red dwarf has a visual luminosity 10% of the Sun's, most have much less, with some as little as 1/10,000th the brightness.

Despite being the most numerous type of stars in the galaxy, no red dwarf is visible in the night sky by the unaided eye even under the best conditions, including the closet star to us, [[Proxima Centauri]]. Even the largest red dwarf has a visual luminosity 10% of the Sun's, most have much less, with some as little as 1/10,000th the brightness.

 

===Planets around red Dwarfs===

===Planets around red Dwarfs===

As the most common type of star in the galaxy, astronomers long wondered if planets orbited any red dwarfs.  Since then several worlds have been found orbiting these stars including the small exoplanet orbiting the red dwarf star '''OGLE-2005-BLG-390L''' with a mass of only 5.5 times that of the Earth.<ref>http://www.nature.com/nature/journal/v439/n7075/full/nature04441.html</ref>  This was the smallest known exoplanet until the discovery of a planet in orbit of [[Gliese 581]] in 2009 called [[Gliese_581#Gliese_581_e|Gliese 581 e]], which has a mass only 1.9 times the Earth.<ref>http://exoplanets.org/planets.shtml</ref>  The red dwarf Gliese 581 also has a world, [[Gliese_581#Gliese_581_d|Gliese 581 d]], which is presently considered a decent candidate for habitability as it sits within the [[habitable zone]] of its parent star.<ref>http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?2007A%26A...476.1365V&db_key=AST&nosetcookie=1</ref>

As the most common type of star in the galaxy, astronomers long wondered if planets orbited any red dwarfs.  Since then several worlds have been found orbiting these stars including the small exoplanet orbiting the red dwarf star '''OGLE-2005-BLG-390L''' with a mass of only 5.5 times that of the Earth.<ref>http://www.nature.com/nature/journal/v439/n7075/full/nature04441.html</ref>  This was the smallest known exoplanet until the discovery of a planet in orbit of [[Gliese 581]] in 2009 called [[Gliese_581#Gliese_581_e|Gliese 581 e]], which has a mass only 1.9 times the Earth.<ref>http://exoplanets.org/planets.shtml</ref>  The red dwarf Gliese 581 also has a world, [[Gliese_581#Gliese_581_d|Gliese 581 d]], which is presently considered a decent candidate for habitability as it sits within the [[habitable zone]] of its parent star.<ref>http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?2007A%26A...476.1365V&db_key=AST&nosetcookie=1</ref>