Editing Double star (section)

==History==
[[Mizar (star)|Mizar]], in [[Ursa Major]], was observed to be double by [[Benedetto Castelli]] and [[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 identification of other doubles soon followed: [[Robert Hooke]] discovered one of the first double-star systems, [[Gamma Arietis]], in 1664,<ref>{{cite book | author = Aitken, Robert G. | title = The Binary Stars | year = 1935 | place = New York | publisher = McGraw-Hill | pages = 1 }}</ref> while the bright southern star [[Alpha Crucis|Acrux]], in the [[Crux|Southern Cross]], was discovered to be double by Fontenay in 1685.<ref name="aitken1"/> Since that time, the search has been carried out thoroughly and the entire sky has been examined for double stars down to a limiting [[apparent magnitude]] of about 9.0.<ref>See ''The Binary Stars'', [[Robert Grant Aitken]], New York: Dover, 1964, pp. 24–25, 38, and p. 61, The present status of double star astronomy, K. Aa. Strand, ''Astronomical Journal'' '''59''' (March 1954), pp. 61–66, {{bibcode|1954AJ.....59...61S}}.</ref> At least 1 in 18 stars brighter than 9.0 [[magnitude (astronomy)|magnitude]] in the northern half of the sky are known to be double stars visible with a {{convert|36|in|mm|adj=on}} [[telescope]].<ref name=aitken260>''The Binary Stars'', [[Robert Grant Aitken]], New York: Dover, 1964, p. 260.</ref>

The unrelated categories of optical doubles and true binaries are lumped together for historical and practical reasons. When Mizar was found to be a binary, it was quite difficult to determine whether a double star was a binary system or only an optical double. Improved telescopes, spectroscopy,<ref>[[Joseph von Fraunhofer|Fraunhofer]], 1814</ref> and photography are the basic tools used to make the distinction. After it was determined to be a visual binary, Mizar's components were found to be spectroscopic binaries themselves.<ref>[[Edward Charles Pickering|Pickering]], 1889</ref>