Editing Binary star (section)

==Discovery==
[[Double star]]s, a pair of stars that appear close to each other, have been observed since the invention of the [[telescope]]. Early examples include [[Mizar]] and [[Acrux]]. Mizar, in the [[Big Dipper]] ([[Ursa Major]]), was observed to be double by [[Giovanni Battista Riccioli]] in 1650<ref name=aitken1>''The Binary Stars'', [[Robert Grant Aitken]], New York: Dover, 1964, p. 1.</ref><ref>[http://leo.astronomy.cz/mizar/riccioli.htm Vol. 1, part 1, p. 422, ''Almagestum Novum'']{{Webarchive| url=https://web.archive.org/web/20110810035504/http://leo.astronomy.cz/mizar/riccioli.htm |date=2011-08-10 }}, Giovanni Battista Riccioli, Bononiae: Ex typographia haeredis Victorij Benatij, 1651.</ref> (and probably earlier by [[Benedetto Castelli]] and [[Galileo Galilei|Galileo]]).<ref name="newviewofmizar">[http://leo.astronomy.cz/mizar/article.htm A New View of Mizar] {{Webarchive|url=https://web.archive.org/web/20080307111656/http://leo.astronomy.cz/mizar/article.htm |date=2008-03-07 }}, Leos Ondra, accessed on line May 26, 2007.</ref> The bright southern star [[Acrux]], in the [[Crux|Southern Cross]], was discovered to be double by Father Fontenay in 1685.<ref name=aitken1 />

Evidence that stars in pairs were more than just optical alignments came in 1767 when English natural philosopher and clergyman [[John Michell]] became the first person to apply the mathematics of statistics to the study of the stars, demonstrating in a paper that many more stars occur in pairs or groups than a perfectly random distribution and chance alignment could account for. He focused his investigation on the [[Pleiades]] cluster, and calculated that the likelihood of finding such a close grouping of stars was about one in half a million. He concluded that the stars in these double or multiple star systems might be drawn to one another by gravitational pull, thus providing the first evidence for the existence of binary stars and star clusters.<ref>This Month in Physics History, November 27, 1783: John Michell anticipates black holes, APS News, November 2009 (Volume 18, Number 10), www.aps.org</ref>

[[William Herschel]] began observing double stars in 1779, hoping to find a near star paired with a distant star so he could measure the near star's changing position as the Earth orbited the Sun (measure its [[parallax]]), allowing him to calculate the distance to the near star. He would soon publish catalogs of about 700 double stars.<ref name="Aitken">{{cite book|last=Aitken|first=Robert Grant|title=The Binary Stars|date=1935|publisher=McGraw-Hill Book Company, Inc.|location=New York and London|isbn=978-1117504094 |pages=4–9|url=https://archive.org/stream/binarystars00aitk#page/4/mode/2up}}</ref><ref name=Heintz4>{{cite book | last=Heintz | first=W. D. | date=1978 | page=[https://archive.org/details/DoubleStars/page/4 4] | title=Double Stars | publisher=D. Reidel Publishing Company | location=Dordrecht | isbn=978-90-277-0885-4 | url=https://archive.org/details/DoubleStars/page/4 }}</ref> By 1803, he had observed changes in the relative positions in a number of double stars over the course of 25 years, and concluded that, instead of showing parallax changes, they seemed to be [[orbit]]ing each other in binary systems.<ref>{{Cite journal |jstor = 107080|title = Account of the Changes That Have Happened, during the Last Twenty-Five Years, in the Relative Situation of Double-Stars; with an Investigation of the Cause to Which They Are Owing|journal = Philosophical Transactions of the Royal Society of London|volume = 93|pages = 339–382|last1 = Herschel|first1 = William|year = 1803|doi = 10.1098/rstl.1803.0015|s2cid = 109971828}}</ref> The first orbit of a binary star was computed in 1827, when [[Félix Savary]] computed the orbit of [[Xi Ursae Majoris]].<ref>p. 291, French astronomers, visual double stars and the double stars working group of the Société Astronomique de France, E. Soulié, ''The Third Pacific Rim Conference on Recent Development of Binary Star Research'', proceedings of a conference sponsored by Chiang Mai University, Thai Astronomical Society and the University of Nebraska-Lincoln held in Chiang Mai, Thailand, 26 October-1 November 1995, ''ASP Conference Series'' '''130''' (1997), ed. Kam-Ching Leung, pp. 291–294, {{bibcode|1997ASPC..130..291S}}.</ref>

Over the years, many more double stars have been catalogued and measured. As of June 2017, the [[Washington Double Star Catalog]], a database of visual double stars compiled by the [[United States Naval Observatory]], contains over 100,000 pairs of double stars,<ref>"Introduction and Growth of the WDS", [http://ad.usno.navy.mil/wds/wdstext.html#intro The Washington Double Star Catalog] {{Webarchive|url=https://web.archive.org/web/20080917194922/http://ad.usno.navy.mil/wds/wdstext.html#intro |date=2008-09-17 }}, Brian D. Mason, Gary L. Wycoff, and William I. Hartkopf, Astrometry Department, [[United States Naval Observatory]], accessed on line August 20, 2008.</ref> including optical doubles as well as binary stars. Orbits are known for only a few thousand of these double stars.<ref>[http://ad.usno.navy.mil/wds/orb6.html Sixth Catalog of Orbits of Visual Binary Stars] {{Webarchive|url=https://web.archive.org/web/20090412084731/http://ad.usno.navy.mil/wds/orb6.html |date=2009-04-12 }}, William I. Hartkopf and Brian D. Mason, [[United States Naval Observatory]], accessed on line August 20, 2008.</ref>