# Binary system > Mediated Wiki article. Canonical URL: https://mediated.wiki/source/Binary_system > Markdown URL: https://mediated.wiki/source/Binary_system.md > Source: https://en.wikipedia.org/wiki/Binary_system > Source revision: 1339224734 > License: Creative Commons Attribution-ShareAlike 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) Two astronomical bodies which orbit each other For binary numbers, see [Binary number](/source/Binary_number). For other uses, see [Binary system (disambiguation)](/source/Binary_system_(disambiguation)). A **binary system** is a system of two [astronomical bodies](/source/Astronomical_bodies) of the same kind that are comparable in size. Definitions vary, but typically require the [center of mass](/source/Barycenter) to be located outside of either object. (See [animated examples](/source/Barycenter#Gallery).) The most common kinds of binary system are [binary stars](/source/Binary_star) and [binary asteroids](/source/Binary_asteroid), but [brown dwarfs](/source/Brown_dwarf), [planets](/source/Planet), [neutron stars](/source/Neutron_star), [black holes](/source/Black_hole) and [galaxies](/source/Galaxies) can also form binaries. A *multiple system* is similar but consists of three or more objects, for example [triple stars](/source/Triple_star) and [triple asteroids](/source/Triple_asteroid) (a more common term than 'trinary'). ## Classification In a binary system, the brighter or more massive object is referred to as *[primary](/source/Primary_(astronomy))*, 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.[1] 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.[2] **Eclipsing binaries** are where the objects' orbits are at an angle that when one passes in front of the other it causes an [eclipse](/source/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.[3][4] ## Binary companion (minor planets) The dwarf planet [Pluto](/source/Pluto) and its moon [Charon](/source/Charon_(moon)) are often described as a binary system in the [Solar System](/source/Solar_System), which orbit the [Sun](/source/Sun). Main article: [Binary asteroid](/source/Binary_asteroid) When binary minor planets are similar in size, they may be called "[binary companions](/source/Binary_asteroid)" instead of referring to the smaller body as a satellite.[5] Good examples of true binary companions are the [90 Antiope](/source/90_Antiope) and the [79360 Sila–Nunam](/source/79360_Sila%E2%80%93Nunam) systems. [Pluto](/source/Pluto) and its largest moon [Charon](/source/Charon_(moon)) are sometimes described as a binary system because the [barycenter](/source/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.[6] [Orcus](/source/90482_Orcus) and its moon [Vanth](/source/Vanth_(moon)) 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. ## See also - [Astronomy portal](https://en.wikipedia.org/wiki/Portal:Astronomy) - [Binary asteroid](/source/Binary_asteroid) - [Binary star](/source/Binary_star) - [Contact binary](/source/Contact_binary) - [Contact binary (small Solar System body)](/source/Contact_binary_(small_Solar_System_body)) - [Double planet](/source/Double_planet) - [Rotational Brownian motion](/source/Rotational_Brownian_motion_(astronomy)) ## References 1. **[^](#cite_ref-1)** updated, Robert Lea last (2018-01-17). ["Binary Star Systems: Classification and Evolution"](https://www.space.com/22509-binary-stars.html). *Space.com*. Retrieved 2025-02-24. {{[cite web](https://en.wikipedia.org/wiki/Template:Cite_web)}}: |last= has generic name ([help](https://en.wikipedia.org/wiki/Help:CS1_errors#generic_name)) 1. **[^](#cite_ref-2)** ["Binary star | Definition, Types, & Facts | Britannica"](https://www.britannica.com/science/binary-star). *www.britannica.com*. Retrieved 2025-02-24. 1. **[^](#cite_ref-3)** ["Binary Star Systems: Classification and Evolution"](http://www.space.com/22509-binary-stars.html). [Space.com](/source/Space.com). 17 January 2018. 1. **[^](#cite_ref-4)** Lehmann, Holger. *Analysis of Spectroscopic Binaries*. [Thüringer Landessternwarte Tautenburg](/source/Th%C3%BCringer_Landessternwarte_Tautenburg). 1. **[^](#cite_ref-IAU-list_5-0)** ["Satellites and Companions of Minor Planets"](https://web.archive.org/web/20110121153650/http://www.cbat.eps.harvard.edu/minorsats.html). IAU / [Minor Planet Center](/source/Minor_Planet_Center). 2009-09-17. Archived from [the original](http://www.cbat.eps.harvard.edu/minorsats.html) on 2011-01-21. Retrieved 2011-01-08. 1. **[^](#cite_ref-6)** Ian O'Neill (8 August 2014). ["Can We Call Pluto and Charon a 'Binary Planet' Yet?"](http://news.discovery.com/space/can-we-call-pluto-and-charon-a-binary-planet-yet-140808.htm). *Discovery News*. Retrieved 15 July 2015. ## External links - [NASA Astrobiology Institute Shows How Wide Binary Stars Form - NASA](https://www.nasa.gov/home/hqnews/2012/dec/HQ_12-425_Wide_Binary_Stars.html) [Archived](https://web.archive.org/web/20161220134705/https://www.nasa.gov/home/hqnews/2012/dec/HQ_12-425_Wide_Binary_Stars.html) 2016-12-20 at the [Wayback Machine](/source/Wayback_Machine) - [OGLE Atlas of Variable Star Light Curves - Eclipsing binaries](https://ogle.astrouw.edu.pl/atlas/eclipsing_binaries.html) ## Bibliography - *Astronomy: A Visual Guide* by Mark A. Garlick --- Adapted from the Wikipedia article [Binary system](https://en.wikipedia.org/wiki/Binary_system) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Binary_system?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.