Editing Star system (section)

==Optical doubles and multiples==

Binary and multiple star systems are also known as a ''physical'' multiple stars, to distinguish them from ''optical'' multiple stars, which merely look close together when viewed from Earth. ''Multiple stars'' may refer to either optical or physical,<ref>{{cite book |author=John R. Percy |year=2007 |title=Understanding Variable Stars |page=16 |publisher=Cambridge University Press |isbn=978-1-139-46328-7 |url=https://books.google.com/books?id=GQzCDQI3YP4C}}</ref><ref name=toko /><ref>{{cite web |website=Hipparcos |title=Double and multiple stars |publisher=[[European Space Agency]] |url=http://www.rssd.esa.int/index.php?project=HIPPARCOS&page=Double_stars |access-date=31 October 2007}}</ref><ref>{{cite web |title=Binary and multiple stars |website=messier.seds.org |url=http://messier.seds.org/bina.html |access-date=26 May 2007}}</ref> but optical multiples do not form a star ''system''.

Triple stars that are ''not'' all gravitationally bound (and thus do not form a triple star system) might comprise a physical binary and an ''optical'' companion (such as [[Beta Cephei]]) or, in rare cases, a purely ''optical'' triple star (such as [[Gamma Serpentis]]).