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[[Image:000Bootes constellation map.jpg|thumb|right|250px|Location of Arcturus (Alpha Boötis) in the constellation of [[Boötes]]. Copyright © 2003 Torsten Bronger[http://en.wikipedia.org/wiki/User:Bronger].  Used with permission.]]

'''Arcturus''', also known as '''Alpha Boötis''', is a star located some 36.7 light years from our [[Sun]].  It is the brightest star in the constellation [[Boötes]].  Arcturus is the fourth brightest star overall in the night sky after [[Sirius]],  [[Canopus]], and [[Alpha Centauri|Alpha Centauri AB]] (the two stars are too close to resolve separately with the unaided eye), and the brightest one located in the northern celestial hemisphere, with an apparent magnitude of -0.05.<ref>http://www.atlasoftheuniverse.com/stars.html</ref>  Arcturus is a single star, although in the 1990's it was thought to possibly have a stellar companion.<ref>http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999PASP..111..556T&db_key=AST&high=3bd70156a918794</ref>

'''Arcturus''', also known as '''Alpha Boötis''', is a star located some 36.7 light years from our [[Sun]].  It is the brightest star in the constellation [[Boötes]].  Arcturus is the fourth brightest star overall in the night sky after [[Sirius]],  [[Canopus]], and [[Alpha Centauri|Alpha Centauri AB]] (the two stars are too close to resolve separately with the unaided eye), and the brightest one located in the northern celestial hemisphere, with an apparent magnitude of -0.05.<ref>http://www.atlasoftheuniverse.com/stars.html</ref>  Arcturus is a single star, although in the 1990's it was thought to possibly have a stellar companion.<ref>http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999PASP..111..556T&db_key=AST&high=3bd70156a918794</ref>

==The Star==

==The Star==

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[[Image:000Arcturus-star.jpg|thumb|right|200px|Comparison in size between Arcturus and the [[Sun]]. Copyright © Windows to the Universe [http://www.windows.ucar.edu/].  Used with permission.]]

Arcturus is an orange-red giant with of the spectral type K1.5 IIIpe.  The star has some 24.5 times the diameter of our [[Sun]].  Like all giants, it has a low mass mass compared to its size, having only 1.5 times the mass of our Sun.<ref name="illinois">http://www.astro.illinois.edu/~jkaler/sow/arcturus.html</ref>  Arcturus is 115 times as bright as our sun visually, although its absolute magnitude is 215 times as great counting the [[infrared]].<ref>http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002hgs..book.....K&db_key=AST&data_type=HTML&format=&high=45e3861c6616357</ref>  The star has rather low [[metallicity]], with only 17 to 32 percent as abundant as our Sun with elements heavier then [[hydrogen]], based on its abundance of [[iron]].<ref>http://adsbit.harvard.edu/cgi-bin/nph-iarticle_query?bibcode=1998Obs...118..299G&data_type=PDF_HIGH&type=PRINTER</ref>

Arcturus is an orange-red giant with of the spectral type K1.5 IIIpe.  The star has some 24.5 times the diameter of our [[Sun]].  Like all giants, it has a low mass mass compared to its size, having only 1.5 times the mass of our Sun.<ref name="illinois">http://www.astro.illinois.edu/~jkaler/sow/arcturus.html</ref>  Arcturus is 115 times as bright as our sun visually, although its absolute magnitude is 215 times as great counting the [[infrared]].<ref>http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002hgs..book.....K&db_key=AST&data_type=HTML&format=&high=45e3861c6616357</ref>  The star has rather low [[metallicity]], with only 17 to 32 percent as abundant as our Sun with elements heavier then [[hydrogen]], based on its abundance of [[iron]].<ref>http://adsbit.harvard.edu/cgi-bin/nph-iarticle_query?bibcode=1998Obs...118..299G&data_type=PDF_HIGH&type=PRINTER</ref>