Editing Alpha Centauri (section)

=== Orbital properties ===
[[File:Orbit Alpha Centauri AB arcsec.png|thumb|upright=1.4|left|Apparent and true orbits of Alpha Centauri. The A component is held stationary, and the relative orbital motion of the B component is shown. The apparent orbit (thin ellipse) is the shape of the orbit as seen by an observer on Earth. The true orbit is the shape of the orbit viewed perpendicular to the plane of the orbital motion. According to the radial velocity versus time,<ref name="Pourbaix">{{cite journal |last=Pourbaix |first= D.|year=2002|title=Constraining the difference in convective blueshift between the components of alpha Centauri with precise radial velocities|journal=Astronomy and Astrophysics|volume=386|issue=1|pages=280–285|bibcode=2002A&A...386..280P|doi=10.1051/0004-6361:20020287|arxiv=astro-ph/0202400|s2cid=14308791|display-authors=et al.}}</ref> the radial separation of A and B along the line of sight had reached a maximum in 2007, with B being further from Earth than A. The orbit is divided here into 80 points: each step refers to a timestep of approx. 0.99888 years or 364.84 days.|alt=Graphic image of a near-circle and a narrow ellipse labelled respectively as "B's real trajectory" and "B's apparent trajectory", with years marked along portions of the ellipses.]]
[[File:Orbital plot of Proxima Centauri.jpg|thumb|upright=1.4|Orbital plot of Proxima Centauri around the bright apparent star Alpha Centauri AB, with position change marked (in thousands of years).]]

The A and B components of Alpha Centauri have an orbital period of 79.762&nbsp;years. Their orbit is moderately [[orbital eccentricity|eccentric]], as it has an eccentricity of almost 0.52;<ref name=Akeson2021/> their closest approach or [[apsis|periastron]] is {{cvt|11.2|AU|e9km}}, or about the distance between the Sun and Saturn; and their furthest separation or [[apsis|apastron]] is {{cvt|35.6|AU|e9km}}, about the distance between the Sun and Pluto.<ref name=SixthCatOrbVisBin/> The most recent [[apsis|periastron]] was in August 1955 and the next will occur in May&nbsp;2035; the most recent [[apsis|apastron]] was in May 1995 and will next occur in 2075.

Viewed from Earth, the apparent orbit of A and B means that their separation and [[position angle]] (PA) are in continuous change throughout their projected orbit. Observed stellar positions in 2019 are separated by 4.92 [[Minute and second of arc|arcsec]] through the PA of 337.1°, increasing to 5.49 arcsec through 345.3° in 2020.<ref name="SixthCatOrbVisBin"/> The closest recent approach was in February 2016, at 4.0 arcsec through the PA of 300°.<ref name="SixthCatOrbVisBin">{{citation-attribution|1={{cite news |last1=Hartkopf|first1=W. |last2=Mason |first2= D. M.|year=2008 |url=http://ad.usno.navy.mil/wds/orb6.html |title=Sixth Catalog of Orbits of Visual Binaries |publisher=U.S. Naval Observatory |access-date=26 May 2008|archive-url=https://web.archive.org/web/20090412084731/http://ad.usno.navy.mil/wds/orb6.html|archive-date=12 April 2009|url-status=dead}} }}</ref><ref>{{cite web |first = Andrew |last = James |url=http://www.southastrodel.com/PageAlphaCen006.htm |title=ALPHA CENTAURI: 6 |website=southastrodel.com |date=11 March 2008 |access-date=12 August 2010}}</ref> The observed maximum separation of these stars is about 22 arcsec, while the minimum distance is 1.7&nbsp;arcsec.<ref name=Aitken>{{cite book |title=The Binary Stars |publisher=Dover |author-link=Robert Grant Aitken |first=R.G. |last=Aitken |pages=235–237 |year=1961}}</ref> The widest separation occurred during February 1976, and the next will be in January 2056.<ref name=SixthCatOrbVisBin/>

Alpha Centauri C is about {{cvt|13000|AU|ly e12km}} from Alpha Centauri AB, equivalent to about 5% of the distance between Alpha Centauri AB and the Sun.<ref name=Kervella2017/><ref name=Matt93/><ref name="adsabs.harvard.edu"/> Until 2017, measurements of its small speed and its trajectory were of too little accuracy and duration in years to determine whether it is bound to Alpha Centauri AB or unrelated.

Radial velocity measurements made in 2017 were precise enough to show that Proxima Centauri and Alpha Centauri AB are gravitationally bound.<ref name=Kervella2017/> The orbital period of Proxima Centauri is approximately {{val|511000|41000|30000}} years, with an eccentricity of 0.5, much more eccentric than [[Mercury (planet)|Mercury]]'s. Proxima Centauri comes within {{val|4100|700|600|ul=AU}} of AB at periastron, and its apastron occurs at {{val|12300|200|100|ul=AU}}.<ref name="Akeson2021"/>