Editing Proxima Centauri (section)

== Observational history ==
[[File:ProximaCentauriLocation.png|thumb|upright=1.5|The location of Proxima Centauri (circled in red)]]In 1915, the Scottish astronomer [[Robert T. A. Innes|Robert Innes]], director of the [[Union Observatory]] in [[Johannesburg]], [[South Africa]], discovered a star that had the same [[proper motion]] as [[Alpha Centauri]].<ref name="Innes1915">{{cite journal |last1=Innes |first1=R. T. A. |date=October 1915 |title=A Faint Star of Large Proper Motion |journal=Circular of the Union Observatory Johannesburg |volume=30 |pages=235–236 |bibcode=1915CiUO...30..235I}} This is the original Proxima Centauri discovery paper.</ref><ref name="afrsky11_39">{{cite journal |last=Glass |first=I. S. |date=July 2007 |title=The discovery of the nearest star |journal=[[African Skies (journal)|African Skies]] |volume=11 |page=39 |bibcode=2007AfrSk..11...39G}}</ref><ref>{{cite web |last=Queloz |first=Didier |date=November 29, 2002 |title=How Small are Small Stars Really? |url=https://www.eso.org/public/news/eso0232/ |access-date=January 29, 2018 |publisher=European Southern Observatory |id=eso0232; PR 22/02}}</ref> He suggested that it be named ''Proxima Centauri''<ref name="aj39_913_20">{{cite journal |last=Alden |first=Harold L. |date=1928 |title=Alpha and Proxima Centauri |journal=Astronomical Journal |volume=39 |issue=913 |pages=20–23 |bibcode=1928AJ.....39...20A |doi=10.1086/104871|doi-access=free }}</ref> (actually ''Proxima Centaurus'').<ref name="Innes1917">{{cite journal |last1=Innes |first1=R. T. A. |date=September 1917 |title=Parallax of the Faint Proper Motion Star Near Alpha of Centaurus. 1900. R.A. 14{{sup|h}}22{{sup|m}}55{{sup|s}}.-0s 6t. Dec-62° 15'2 0'8 t |journal=Circular of the Union Observatory Johannesburg |volume=40 |pages=331–336 |bibcode=1917CiUO...40..331I}}</ref> In 1917, at the [[Royal Observatory, Cape of Good Hope|Royal Observatory]] at the [[Cape of Good Hope]], the Dutch astronomer [[Joan Voûte]] measured the star's trigonometric [[parallax]] at {{val|0.755|0.028|ul=″}} and determined that Proxima Centauri was approximately the same distance from the Sun as Alpha Centauri. It was the lowest-[[luminosity]] star known at the time.<ref name="Voûte1917">{{cite journal |last=Voûte |first=J. |date=1917 |title=A 13th magnitude star in Centaurus with the same parallax as α Centauri |url=https://zenodo.org/record/1431901 |journal=[[Monthly Notices of the Royal Astronomical Society]] |volume=77 |issue=9 |pages=650–651 |bibcode=1917MNRAS..77..650V |doi=10.1093/mnras/77.9.650 |doi-access=free}}</ref> An equally accurate parallax determination of Proxima Centauri was made by American astronomer [[Harold Lee Alden|Harold L. Alden]] in 1928, who confirmed Innes's view that it is closer, with a parallax of {{val|0.783|0.005|u=″}}.<ref name="afrsky11_39" /><ref name="aj39_913_20" />

A size estimate for Proxima Centauri was obtained by the Canadian astronomer [[John Stanley Plaskett]] in 1925 using [[interferometry]]. The result was 207,000 miles (333,000 km), or approximately {{Solar radius|0.24}}.<ref>{{Cite journal |last=Plaskett |first=J. S. |date=1922 |title=The Dimensions of the Stars |url=https://www.jstor.org/stable/40668597 |journal=Publications of the Astronomical Society of the Pacific |volume=34 |issue=198 |pages=79–93 |doi=10.1086/123157 |jstor=40668597 |bibcode=1922PASP...34...79P |issn=0004-6280}}</ref>

In 1951, American astronomer [[Harlow Shapley]] announced that Proxima Centauri is a [[flare star]]. Examination of past photographic records showed that the star displayed a measurable increase in magnitude on about 8% of the images, making it the most active flare star then known.<ref>{{cite journal |last=Shapley |first=Harlow |date=1951 |title=Proxima Centauri as a flare star |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=37 |issue=1 |pages=15–18 |bibcode=1951PNAS...37...15S |doi=10.1073/pnas.37.1.15 |pmc=1063292 |pmid=16588985 |doi-access=free}}</ref><ref>{{cite journal |last1=Kroupa |first1=Pavel |last2=Burman |first2=R. R. |last3=Blair |first3=D. G. |date=1989 |title=Photometric observations of flares on Proxima Centauri |journal=PASA |volume=8 |issue=2 |pages=119–122 |bibcode=1989PASA....8..119K |doi=10.1017/S1323358000023122|s2cid=117977034 }}</ref>
The proximity of the star allows for detailed observation of its flare activity. In 1980, the [[Einstein Observatory]] produced a detailed X-ray energy curve of a stellar flare on Proxima Centauri. Further observations of flare activity were made with the [[EXOSAT]] and [[ROSAT]] [[satellite]]s, and the X-ray emissions of smaller, solar-like flares were observed by the Japanese [[Advanced Satellite for Cosmology and Astrophysics|ASCA]] satellite in 1995.<ref>{{cite journal |last1=Haisch |first1=Bernhard |last2=Antunes |first2=A. |last3=Schmitt |first3=J. H. M. M. |date=1995 |title=Solar-like M-class X-ray flares on Proxima Centauri observed by the ASCA satellite |journal=Science |volume=268 |issue=5215 |pages=1327–1329 |bibcode=1995Sci...268.1327H |doi=10.1126/science.268.5215.1327 |pmid=17778978 |s2cid=46660210}}</ref> Proxima Centauri has since been the subject of study by most X-ray observatories, including [[XMM-Newton]] and [[Chandra X-ray Observatory|Chandra]].<ref name="aaa416" />

Because of Proxima Centauri's southern declination, it can only be viewed south of [[latitude]] [[27th parallel north|27°&nbsp;N]].<ref group="nb">For a star south of the zenith, the angle to the zenith is equal to the Latitude minus the Declination. The star is hidden from sight when the zenith angle is 90° or more, i.e., below the horizon. Thus, for Proxima Centauri:

:Highest latitude = 90° + (−62.68°) = 27.32°.
See: {{cite book |last=Campbell |first=William Wallace |url=https://archive.org/details/elementspractic00campgoog |title=The elements of practical astronomy |date=1899 |publisher=Macmillan |location=London |pages=[https://archive.org/details/elementspractic00campgoog/page/n129 109]–110 |access-date=August 12, 2008}}</ref> Red dwarfs such as Proxima Centauri are too faint to be seen with the naked eye. Even from Alpha Centauri A or B, Proxima would only be seen as a fifth magnitude star.<ref>{{cite web |title=Proxima Centauri UV flux distribution |url=http://sdc.cab.inta-csic.es/ines/Ines_PCentre/Demos/Fluxdist/pcentauri.html |access-date=July 11, 2007 |publisher=ESA & The Astronomical Data Centre at CAB}}</ref><ref>{{cite web |last=Kaler |first=James B. |author-link=James B. Kaler |date=November 7, 2016 |title=Rigil Kentaurus |url=http://stars.astro.illinois.edu/sow/rigil-kent.html |access-date=August 3, 2008 |work=STARS |publisher=University of Illinois}}</ref> It has [[apparent visual magnitude]]&nbsp;11, so a [[telescope]] with an [[aperture]] of at least {{convert|8|cm|abbr=on}} is needed to observe it, even under ideal viewing conditions—under clear, dark skies with Proxima Centauri well above the horizon.<ref>{{cite book |last1=Sherrod |first1=P. Clay |title=A complete manual of amateur astronomy: tools and techniques for astronomical observations |last2=Koed |first2=Thomas L. |date=2003 |publisher=Courier Dover Publications |isbn=978-0-486-42820-8}}</ref> In 2016, the [[International Astronomical Union]] organized a [[IAU Working Group on Star Names|Working Group on Star Names]] (WGSN) to catalogue and standardize proper names for stars.<ref name="WGSN">{{cite web |title=IAU Working Group on Star Names (WGSN) |url=https://www.iau.org/science/scientific_bodies/working_groups/280/ |access-date=May 22, 2016 |publisher=International Astronomical Union}}</ref> The WGSN approved the name ''Proxima Centauri'' for this star on August 21, 2016, and it is now so included in the List of IAU approved Star Names.<ref name="IAU-LSN">{{cite web |title=Naming Stars |url=https://www.iau.org/public/themes/naming_stars/ |access-date=March 3, 2018 |publisher=International Astronomical Union}}</ref>

In 2016, a [[superflare]] was observed from Proxima Centauri, the strongest flare ever seen. The optical brightness increased by a factor of 68× to approximately magnitude&nbsp;6.8. It is estimated that similar flares occur around five times every year but are of such short duration, just a few minutes, that they have never been observed before.<ref name="howard">{{cite journal |last1=Howard |first1=Ward S. |last2=Tilley |first2=Matt A. |last3=Corbett |first3=Hank |last4=Youngblood |first4=Allison |last5=Loyd |first5=R. O. Parke |last6=Ratzloff |first6=Jeffrey K. |last7=Law |first7=Nicholas M. |last8=Fors |first8=Octavi |last9=Del Ser |first9=Daniel |last10=Shkolnik |first10=Evgenya L. |last11=Ziegler |first11=Carl |year=2018 |title=The First Naked-eye Superflare Detected from Proxima Centauri |journal=The Astrophysical Journal |volume=860 |issue=2 |pages=L30 |arxiv=1804.02001 |bibcode=2018ApJ...860L..30H |doi=10.3847/2041-8213/aacaf3 |last12=Goeke |first12=Erin E. |last13=Pietraallo |first13=Aaron D. |last14=Haislip |first14=Joshua |s2cid=59127420 |doi-access=free }}</ref> On 2020 April&nbsp;22 and 23, the ''[[New Horizons]]'' spacecraft took images of two of the nearest stars, Proxima Centauri and [[Wolf 359]]. When compared with Earth-based images, a very large parallax effect was easily visible. However, this was only used for illustrative purposes and did not improve on previous distance measurements.<ref>{{cite web |date=29 January 2020 |title=Seeing Stars in 3D: The New Horizons Parallax Program |url=http://pluto.jhuapl.edu/News-Center/News-Article.php?page=20200129 |access-date=25 May 2020 |website=pluto.jhuapl.edu |publisher=Johns Hopkins University Applied Physics Laboratory}}</ref><ref>{{cite web |title=Parallax measurements for Wolf 359 and Proxima Centauri |url=https://www.dlr.de/content/en/images/2020/3/parallax-measurements-wolf-359-and-proxima-centauri.html |access-date=19 January 2021 |website=German Aerospace Center}}</ref>