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'''Kapteyn's Star''' is one of the closest stars to our solar system, the star is noted for it's unusual features compared to other local stars such as it's retrograde galactic orbital path, extreme age, and origins outside the galactic plane.  The star was first discovered by  Jacobus Cornelius Kapteyn (1851-1922) and Robert Thorburn Ayton Innes in 1897<ref name="sol">http://www.solstation.com/stars/kapteyns.htm</ref> and was found to have the greatest proper motion until the discovery of [[Barnard's Star]].

'''Kapteyn's Star''' is one of the closest stars to our solar system.  The star is noted for it's unusual features compared to other local stars, such as it's retrograde galactic orbital path, extreme age, and origins outside the galactic plane.  The star was first discovered by  Jacobus Cornelius Kapteyn (1851-1922) and Robert Thorburn Ayton Innes in 1897<ref name="sol">http://www.solstation.com/stars/kapteyns.htm</ref> and was found to have the greatest proper motion of any star until the discovery of [[Barnard's Star]].

Kapteyn's Star itself is classified as a sdM1V halo star<ref>http://adsbit.harvard.edu/cgi-bin/nph-iarticle_query?1997AJ....113..806G</ref>, meaning it's origins are from the [[Milky Way|Milky Way's]] [[galactic halo]], a spherical region around the [[galaxy]] containing very old, [[Metallicity|metal-poor]] stars.  Because the star is a dim M class dwarf with only 4/1000th of the sun, it has an apparent magnitude of 8.85, rendering it invisible to the unaided eye, this despite being located only 12.77 years away, making it the 25th closest star. Kapteyn's Star has only 10.5 percent of the Metallicity of Sol, 29 to 39.3 percent of Sol's mass<ref>http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004MNRAS.350..575W&db_key=AST&high=41dd40b72e13373</ref>, and less than third (29 to 32 percent) of its diameter<ref name="sol">http://www.solstation.com/stars/kapteyns.htm</ref>.

Kapteyn's Star itself is classified as a sdM1V halo star<ref>http://adsbit.harvard.edu/cgi-bin/nph-iarticle_query?1997AJ....113..806G</ref>, meaning it's origins are from the [[Milky Way|Milky Way's]] [[galactic halo]], a spherical region around the [[galaxy]] containing very old, [[Metallicity|metal-poor]] stars.  Because the star is a dim M class dwarf with only 4/1000th of the sun's brightness, it has an apparent magnitude of 8.85, rendering it invisible to the unaided eye despite being located only 12.77 years away, making it the 25th closest star. Kapteyn's Star has only 10.5 percent of the Metallicity of Sol, 29 to 39.3 percent of Sol's mass<ref>http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004MNRAS.350..575W&db_key=AST&high=41dd40b72e13373</ref>, and less than third (29 to 32 percent) of its diameter<ref name="sol">http://www.solstation.com/stars/kapteyns.htm</ref>.

Because Kapteyn's Star is so metal-poor (lacking in elements heavier then [[hydrogen]] and [[helium]]), it appears more bluish and dimmer then the typical younger, main sequence M-class dwarf<ref>http://adsbit.harvard.edu/cgi-bin/nph-iarticle_query?1976ApJ...205..186W</ref>.  Due of the lack of metals, it is generally accepted the star was born in an earlier age and/or region such as the galatic halo where few [[supernova]] have released their metals into the surrounding region (supernova being the general source of all elements above helium on the [[periodic table]]).

Because Kapteyn's Star is so metal-poor (lacking in elements heavier then [[hydrogen]] and [[helium]]), it appears more bluish and dimmer then the typical younger, main sequence M-class dwarf<ref>http://adsbit.harvard.edu/cgi-bin/nph-iarticle_query?1976ApJ...205..186W</ref>.  Due of the lack of metals, it is generally accepted the star was born in an earlier age and/or region such as the galatic halo where few [[supernova]] have released their metals into the surrounding region (supernova being the general source of all elements above helium on the [[periodic table]]).

Very few such halo stars are located near our solar system with such stars accounting for only 0.1 to 0.2 percent of all stars that are near the sun, Kapteyn's Star is believed to be the closest of these.  The star is a member of a local cluster of halo stars that is very thinly spread out over a distance of some 6,500 to 9,800 light-years stretching towards the galactic halo<ref>http://adsbit.harvard.edu/cgi-bin/nph-iarticle_query?1996AJ....112.2661E</ref>.  Kapteyn's Star is usual because most such stars lie far above or below the galactic plane.  Like other halo stars, Kapteyn's Star does have an extremely elliptical galactic orbit and is believed to be among the oldest star's in the galaxy and the region around it, estimated to be some 10 billion years old or older.

Very few such halo stars are located near our solar system, with such stars accounting for only 0.1 to 0.2 percent of all stars that are near the sun. Kapteyn's Star is believed to be the closest of these.  The star is a member of a local cluster of halo stars that is very thinly spread out over a distance of some 6,500 to 9,800 light-years stretching towards the galactic halo<ref>http://adsbit.harvard.edu/cgi-bin/nph-iarticle_query?1996AJ....112.2661E</ref>.  Kapteyn's Star is unusual because most such stars lie far above or below the galactic plane.  Like other halo stars, Kapteyn's Star does have an extremely elliptical galactic orbit and is believed to be among the oldest star's in the galaxy and the region around it, estimated to be some 10 billion years old or older.

There are no known sub-stellar companions around Kapteyn's Star at this time, the star however is classified as a "Tier 1" target star for [[NASA|NASA's]] optical [[Space Interferometry Mission]] that will search for rocky worlds due to it's proximity to our system.  For an [[Earth]] like world to have liquid water on it's surface, the world would have to be around 0.26 AUs from the star, or about half of [[Mercury|Mercury's]] distance from the sun, such a world would be tidally locked to the star<ref name="sol">http://www.solstation.com/stars/kapteyns.htm</ref>.

There are no known sub-stellar companions around Kapteyn's Star at this time. However the star is classified as a "Tier 1" target star for [[NASA|NASA's]] optical [[Space Interferometry Mission]] that will search for rocky worlds, due to it's proximity to our system.  For an [[Earth]]-like world to have liquid water on it's surface, the world would have to be around 0.26 AUs from the star, or about half of [[Mercury|Mercury's]] distance from the sun. Such a world would be tidally locked to the star<ref name="sol">http://www.solstation.com/stars/kapteyns.htm</ref>.

[[Category:Astronomy]]

[[Category:Astronomy]]