Editing Double star (section)

==Designations==
Some bright visual double stars have a [[Bayer designation]]. In this case, the components may be denoted by superscripts. An example of this is [[α Crucis]] (Acrux), whose components are α<sup>1</sup> Crucis and α<sup>2</sup> Crucis. Since α<sup>1</sup> Crucis is a [[spectroscopic binary]], this is actually a multiple star. Superscripts are also used to distinguish more distant, physically unrelated, pairs of stars with the same Bayer designation, such as [[Alpha Capricorni|α<sup>1,2</sup> Capricorni]], [[Xi Centauri|ξ<sup>1,2</sup> Centauri]], and [[Xi Sagittarii|ξ<sup>1,2</sup> Sagittarii]]. These optical pairs are resolvable by the naked eye.

Apart from these pairs, the components of a double star are generally denoted by the letters A (for the brighter, ''primary'', star) and B (for the fainter, ''secondary'', star) appended to the designation, of whatever sort, of the double star. For example, the components of [[α Canis Majoris]] (Sirius) are α Canis Majoris A and α Canis Majoris B (Sirius A and Sirius B); the components of [[44 Boötis]] are 44 Boötis A and 44 Boötis B; the components of [[ADS 16402]] are ADS 16402A and ADS 16402B; and so on. The letters AB may be used together to designate the pair. In the case of multiple stars, the letters C, D, and so on may be used to denote additional components, often in order of increasing separation from the brightest star, A.<ref name=Heintz19>{{cite book | last=Heintz | first=W. D. | year=1978 | page=[https://archive.org/details/DoubleStars/page/19 19] | title=Double Stars | publisher=D. Reidel Publishing Company | location=Dordrecht | isbn=90-277-0885-1 | url=https://archive.org/details/DoubleStars/page/19 }}</ref>

{| class="wikitable" : style="float:right; margin:1em 1em"
|+ Double star discoverer designations<ref name=argyle307308 />
|-
! Discoverer
! Traditional code
! WDS code
|-
| [[Parramatta Observatory|Brisbane Observatory]]
| Brs0
| BSO
|-
| [[S. W. Burnham]]
| β
| BU
|-
| [[James Dunlop]]
| Δ
| DUN
|-
| [[William Herschel]]
| H I, II, etc.
| H 1, 2, etc.
|-
| [[N. Lacaille]]
| Lac
| LCL
|-
| [[F. G. W. Struve]]
| Σ
| STF
|-
| Struve Appendix Catalogue I
| Σ I
| STFA
|-
| Struve Appendix Catalogue II
| Σ II
| STFB
|-
| [[Otto Struve]]
| OΣ
| STT
|-
| Pulkova Appendix Catalogue
| OΣΣ
| STTA
|}
Visual doubles are also designated by an abbreviation for the name of their discoverer followed by a catalogue number unique to that observer. For example, the pair α Centauri AB was discovered by Father Richaud in 1689, and so is designated ''RHD 1''.<ref name=aitken1 /><ref>Entry 14396-6050, discoverer code RHD 1AB,[http://ad.usno.navy.mil/wds/Webtextfiles/wdsnewframe3.html The Washington Double Star Catalog] {{Webarchive|url=https://archive.today/20120708194616/http://ad.usno.navy.mil/wds/Webtextfiles/wdsnewframe3.html |date=2012-07-08 }}, [[United States Naval Observatory]]. Accessed on line August 20, 2008.</ref> Other examples include Δ65, the 65th double discovered by [[James Dunlop]], and Σ2451, discovered by [[F. G. W. Struve]].

The [[Washington Double Star Catalog]], a large database of double and multiple stars, contains over 100,000 entries,<ref name=wdsintro /> each of which gives measures for the separation of two components. Each double star forms one entry in the catalog; multiple stars with ''n'' components will be represented by entries in the catalog for ''n''−1 pairs, each giving the separation of one component of the multiple star from another. Codes such as AC are used to denote which components are being measured—in this case, component C relative to component A. This may be altered to a form such as AB-D to indicate the separation of a component from a close pair of components (in this case, component D relative to the pair AB.) Codes such as ''Aa'' may also be used to denote a component which is being measured relative to another component, A in this case.<ref>[http://ad.usno.navy.mil/wds/wdsweb_format.txt Format of the current WDS] {{webarchive |url=https://web.archive.org/web/20080412092018/http://ad.usno.navy.mil/wds/wdsweb_format.txt |date=April 12, 2008 }}, Washington Double Star Catalog, [[United States Naval Observatory]]. Accessed on line August 26, 2008.</ref> Discoverer designations are also listed; however, traditional discoverer abbreviations such as Δ and Σ have been encoded into a string of uppercase Roman letters, so that, for example, Δ65 has become DUN&nbsp;&nbsp;65 and Σ2451 has become STF 2451. Further examples of this are shown in the adjacent table.<ref name=argyle307308>p. 307–308, ''Observing and Measuring Double Stars'', Bob Argyle, ed., London: Springer-Verlag, 2004, {{ISBN|1-85233-558-0}}.</ref><ref>[http://ad.usno.navy.mil/wds/wdsnewref.txt References and discoverer codes, The Washington Double Star Catalog] {{Webarchive|url=https://web.archive.org/web/20080413021722/http://ad.usno.navy.mil/wds/wdsnewref.txt |date=2008-04-13 }}, [[United States Naval Observatory]]. Accessed on line August 20, 2008.</ref>