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A binary system is a system of two astronomical bodies of the same kind that are comparable in size. Definitions vary, but typically require the center of mass to be located outside of either object. (See animated examples.)

The most common kinds of binary system are binary stars and binary asteroids, but brown dwarfs, planets, neutron stars, black holes and galaxies can also form binaries.

A multiple system is similar but consists of three or more objects, for example trinary stars and trinary asteroids.

Classification

In a binary system, the brighter or more massive object is referred to as primary, and the other the secondary.

Binary stars are also classified based on orbit. Wide binaries are objects with orbits that keep them apart from one another. They evolve separately and have very little effect on each other. Close binaries are close to each other and are able to transfer mass from one another. They can also be classified based on how we observe them. Visual binaries are two stars separated enough that they can be distinguished through binoculars or a small telescope.

Eclipsing binaries are where the objects' orbits are at an angle that when one passes in front of the other it causes an eclipse, as seen from Earth.

Astrometric binaries are objects that seem to move around nothing as their companion object cannot be identified, it can only be inferred. The companion object may not be bright enough or may be hidden in the glare from the primary object.

A related classification though not a binary system is optical binary, which refers to objects that are so close together in the sky that they appear to be a binary system, but are not. Such objects merely appear to be close together, but lie at different distances from the Solar System.^[1]^[2]

Binary companion (minor planets)

When binary minor planets are similar in size, they may be called "binary companions" instead of referring to the smaller body as a satellite.^[3] Good examples of true binary companions are the 90 Antiope and the 79360 Sila–Nunam systems. Pluto and its largest moon Charon are sometimes described as a binary system because the barycenter (center of mass) of the two objects is not inside either of them, but Charon is small enough compared to Pluto that it is usually classified as a moon.^[4] Orcus and its moon Vanth also orbit around a barycenter not inside either of them. The Sun and Jupiter orbit a point outside of either, but are not considered a binary because they are different kinds of objects.

References

^ "Binary Star Systems: Classification and Evolution". Space.com. 17 January 2018.
^ Lehmann, Holger. Analysis of Spectroscopic Binaries. Thüringer Landessternwarte Tautenburg.
^ "Satellites and Companions of Minor Planets". IAU / Minor Planet Center. 2009-09-17. Archived from the original on 2011-01-21. Retrieved 2011-01-08.
^ Ian O'Neill (8 August 2014). "Can We Call Pluto and Charon a 'Binary Planet' Yet?". Discovery News. Retrieved 15 July 2015.

External links

Bibliography

Astronomy: A Visual Guide by Mark A. Garlick

[1] "Binary Star Systems: Classification and Evolution". Space.com. 17 January 2018.

[2] Lehmann, Holger. Analysis of Spectroscopic Binaries. Thüringer Landessternwarte Tautenburg.

[IAU-list-3] "Satellites and Companions of Minor Planets". IAU / Minor Planet Center. 2009-09-17. Archived from the original on 2011-01-21. Retrieved 2011-01-08.

[4] Ian O'Neill (8 August 2014). "Can We Call Pluto and Charon a 'Binary Planet' Yet?". Discovery News. Retrieved 15 July 2015.

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+{{short description|Two astronomical bodies which orbit each other}}
+{{hatnote group|
+{{For|binary numbers|Binary number}}
 {{other uses}}
+}}
 {{Refimprove|date=February 2015}}
-A '''binary system''' is a system of two [[astronomical bodies]] which are close enough that their [[gravitational]] attraction causes them to [[orbit]] each other around a [[barycenter]] ''(also see [[Barycenter#Gallery|animated examples]])''. More restrictive definitions require that this common center of mass is not located within the interior of either object, in order to exclude the typical planet–[[Natural satellite|satellite]] systems and planetary systems.
+A '''binary system''' is a system of two [[astronomical bodies]] of the same kind that are comparable in size. Definitions vary, but typically require the [[barycenter|center of mass]] to be located outside of either object. (See [[Barycenter#Gallery|animated examples]].)
-The most common binary systems are [[binary star]]s and [[binary asteroid]], but [[brown dwarf]]s, [[planet]]s, [[neutron star]]s, [[black hole]]s and [[galaxies]] can also form binaries.
+The most common kinds of binary system are [[binary star]]s and [[binary asteroid]]s, but [[brown dwarf]]s, [[planet]]s, [[neutron star]]s, [[black hole]]s and [[galaxies]] can also form binaries.
-A ''multiple system'' is like a binary system but consists of three or more objects such as for [[trinary star]]s and [[trinary asteroid]]s.
+A ''multiple system'' is similar but consists of three or more objects, for example [[trinary star]]s and [[trinary asteroid]]s.
 == Classification ==
+In a binary system, the brighter or more massive object is referred to as '''[[primary (astronomy)|primary]]''', and the other the '''secondary'''.
+Binary stars are also classified based on orbit. '''Wide binaries''' are objects with orbits that keep them apart from one another. They evolve separately and have very little effect on each other. '''Close binaries''' are close to each other and are able to transfer mass from one another. They can also be classified based on how we observe them. '''Visual binaries''' are two stars separated enough that they can be distinguished through binoculars or a small telescope.
-In a binary system the brighter object is referred to as '''primary''', and the other the '''secondary'''.
-They are also classified based on orbit. '''Wide binaries''' are objects with orbits that keep them apart from one another. They evolve separately and have very little effect on each other. '''Close binaries''' are close to each other and are able to transfer mass from one another.
-They can also be classified based on how we observe them. '''Visual binaries''' are two stars separated enough that they can be viewed through a telescope or binoculars.
 '''Eclipsing binaries''' are where the objects' orbits are at an angle that when one passes in front of the other it causes an [[eclipse]], as seen from Earth.
@@ Line 20: / Line 21: @@
 '''Astrometric binaries''' are objects that seem to move around nothing as their companion object cannot be identified, it can only be inferred. The companion object may not be bright enough or may be hidden in the glare from the primary object.
-A related classification though not a binary system is '''Optical binary''' which refers to objects that are so close together in the sky that they appear to be a binary system but are not. Such objects merely appear to be close together, but lie at different distances from the solar system.<ref>{{Cite web |url=http://www.space.com/22509-binary-stars.html |title=Binary Star Systems: Classification and Evolution |publisher=[[Space.com]]}}</ref><ref>{{Cite web |publisher= [[Thüringer Landessternwarte Tautenburg]] |title=Analysis of Spectroscopic Binaries |author=Holger Lehmann}}</ref>
+A related classification though not a binary system is '''optical binary''', which refers to objects that are so close together in the sky that they appear to be a binary system, but are not. Such objects merely appear to be close together, but lie at different distances from the Solar System.<ref>{{cite web |url=http://www.space.com/22509-binary-stars.html |title=Binary Star Systems: Classification and Evolution |date=17 January 2018 |publisher=[[Space.com]]}}</ref><ref>{{cite book |publisher= [[Thüringer Landessternwarte Tautenburg]] |title=Analysis of Spectroscopic Binaries |first=Holger |last=Lehmann}}</ref>
 == Binary companion (minor planets) ==
-[[File:Pluto-Charon System.gif|thumb|right|Pluto and its moon Charon are often described as a binary system.]]
+[[File:Pluto-Charon_system-new.gif|thumb|right|The dwarf planet [[Pluto]] and its moon [[Charon (moon)|Charon]] are often described as a binary system in the [[Solar System]], which orbit the [[Sun]].]]
 {{main|Binary asteroid}}
-When binary minor planets are similar in size, they may be called "[[Binary asteroid|binary companions]]" instead of referring to the smaller body as a satellite.<ref name="IAU-list">{{cite web |date=2009-09-17 |title=Satellites and Companions of Minor Planets |publisher=IAU / [[Minor Planet Center]] |url=http://www.cbat.eps.harvard.edu/minorsats.html |accessdate=2011-01-08 |deadurl=yes |archiveurl=https://web.archive.org/web/20110121153650/http://www.cbat.eps.harvard.edu/minorsats.html |archivedate=2011-01-21 |df= }}</ref> Good examples of true binary companions are the [[90 Antiope]] and the [[79360 Sila–Nunam]] systems. [[Pluto]] and its largest moon [[Charon (moon)|Charon]] are sometimes described as a binary system because the [[barycenter]] (center of mass) of the two objects is not inside either of them.<ref>{{cite web |url=http://news.discovery.com/space/can-we-call-pluto-and-charon-a-binary-planet-yet-140808.htm |title=Can We Call Pluto and Charon a 'Binary Planet' Yet? |author=Ian O'Neill |website=Discovery News |date=8 August 2014 |accessdate=15 July 2015}}</ref>
+When binary minor planets are similar in size, they may be called "[[Binary asteroid|binary companions]]" instead of referring to the smaller body as a satellite.<ref name="IAU-list">{{cite web |date=2009-09-17 |title=Satellites and Companions of Minor Planets |publisher=IAU / [[Minor Planet Center]] |url=http://www.cbat.eps.harvard.edu/minorsats.html |access-date=2011-01-08 |url-status=dead |archive-url=https://web.archive.org/web/20110121153650/http://www.cbat.eps.harvard.edu/minorsats.html |archive-date=2011-01-21 }}</ref> Good examples of true binary companions are the [[90 Antiope]] and the [[79360 Sila–Nunam]] systems. [[Pluto]] and its largest moon [[Charon (moon)|Charon]] are sometimes described as a binary system because the [[barycenter]] (center of mass) of the two objects is not inside either of them, but Charon is small enough compared to Pluto that it is usually classified as a moon.<ref>{{cite web |url=http://news.discovery.com/space/can-we-call-pluto-and-charon-a-binary-planet-yet-140808.htm |title=Can We Call Pluto and Charon a 'Binary Planet' Yet? |author=Ian O'Neill |website=Discovery News |date=8 August 2014 |access-date=15 July 2015}}</ref> [[90482 Orcus|Orcus]] and its moon [[Vanth_(moon)|Vanth]] also orbit around a barycenter not inside either of them.
+The Sun and Jupiter orbit a point outside of either, but are not considered a binary because they are different kinds of objects.
-==In popular culture==
-{{main|Binary stars in fiction}}
-*In the Discovery program ''[[Alien Planet]]'', the planet [[Darwin IV]] orbits a binary system.
-*In ''[[The Hitchhiker's Guide to the Galaxy (novel)|The Hitchhiker's Guide to the Galaxy]]'', the planet [[Places in The Hitchhiker's Guide to the Galaxy#Magrathea|Magrathea]] orbits a binary system
-*In the ''[[Invader Zim]]'' episode "Planet Jackers", one of the aforementioned Jackers mentions a binary system.
-*Binary sun systems are featured in the ''[[Mass Effect 2]]'' game, these systems are in the [[Milky Way]] as explorable areas.
 ==See also==
@@ Line 49: / Line 44: @@
 ==External links==
 *[https://www.nasa.gov/home/hqnews/2012/dec/HQ_12-425_Wide_Binary_Stars.html NASA Astrobiology Institute Shows How Wide Binary Stars Form - NASA]
+*[https://ogle.astrouw.edu.pl/atlas/eclipsing_binaries.html OGLE Atlas of Variable Star Light Curves - Eclipsing binaries]
 ==Bibliography==
@@ Line 54: / Line 50: @@
 [[Category:Celestial mechanics]]
-[[Category:Binary stars| Binary system]]
+[[Category:Binary systems| Binary system]]
 [[Category:Astronomical dynamical systems]]