What is Capella?
[[File:Capella-Sun comparison.png|thumb|right|250px|Capella{{ndash}}Sun comparison]] [[File:Auriga constellation map.png|thumb|right|250px|Capella is the brightest star in Auriga]] '''Capella''' (α Aurigae, α Aur, [[alpha (letter)|Alpha]] Aurigae) is the brightest star in the [[constellation]] [[Auriga (constellation)|Auriga]], the eleventh brightest star in the night sky and the third brightest star in the northern [[Celestial sphere|celestial hemisphere]], after [[Arcturus]] and [[Vega]]. Although it appears to be a single star to the naked eye, it is actually a [[star system]] of four stars in two [[binary star|binary pair]]s. The first pair consists of two bright, large [[Stellar classification|type-G]] [[giant star]]s, both with a radius about 10 times the Sun's, in close orbit around each other. These two stars are thought to be cooling and expanding on their way to becoming [[red giant]]s. The second pair, around 10,000 [[astronomical unit]]s from the first, consists of two faint, small and relatively cool [[red dwarf]]s.<ref>Kaler, James B. 2002. Capella, in ''The hundred greatest stars'', Springer. {{ISBN|0-387-95436-8}} (see §18); {{doi|10.1007/0-387-21625-1_19}}.</ref><ref name=chl>Ayres T.R. 1984. Capella HL. In ''Cool stars, stellar systems, and the Sun'', edited by Sallie L. Baliunas and Lee Hartmann, Berlin/Heidelberg, Springer-Verlag, 1984, Lecture Notes in Physics, '''193''', pp. 202–204.</ref> The Capella system is relatively close, at only {{convert|42.2|ly|pc|lk=on}} from Earth. The system is a member of the Hyades moving group, a group of stars moving in the same direction as the [[Hyades cluster]].<ref>Famaey B. ''et al''. 2007. The Hyades stream: an evaporated cluster or an intrusion from the inner disk? ''Astronomy and Astrophysics'' '''461''', #3, 957–962. [http://www.aanda.org/index.php?option=com_article&access=doi&doi=10.1051/0004-6361:20065706&Itemid=129]</ref> == References == {{Reflist}} [[Category:Binary stars]]