Editing 61 Cygni (section)

=== Parallax measurement ===
A number of astronomers soon took up the task, including attempts by [[François Arago]] and [[Claude-Louis Mathieu]] in 1812, who recorded the parallax at 500&nbsp;[[minute of arc|milliarcseconds]] (mas), and [[Christian Heinrich Friedrich Peters]] used Arago's data to calculate a value of 550&nbsp;mas. Peters calculated a better value based on observations made by [[Bernhard von Lindenau]] at Seeburg between 1812 and 1814; he calculated it to be 470 ±510&nbsp;mas. Von Lindenau had already noted that he had seen no parallax, and as [[Friedrich Georg Wilhelm von Struve]] pointed out after his own test series between 1818 and 1821, all of these numbers are more accurate than the accuracy of the instrument used.<ref name="hopkins-1916" />

[[Friedrich Wilhelm Bessel]] made a notable contribution in 1812 when he used a different method to measure distance. Assuming the [[orbital period]] of the two stars in the binary to be 400 years, he estimated the distance between the two this would require, and then measured the [[angular distance]] between the stars. This led to a value of 460&nbsp;mas.{{citation needed|date=April 2019}} He then followed this up with direct parallax measurements in a series of observations between 1815 and 1816, comparing it with six other stars. The two sets of measurements produced values of 760 and 1320&nbsp;mas. All of these estimates, like earlier attempts by others, retained inaccuracies greater than the measurements.<ref name="hopkins-1916" />

When [[Joseph von Fraunhofer]] invented a new type of [[heliometer]], Bessel carried out another set of measurements using this device in 1837 and 1838 at [[Königsberg]]. He published his findings in 1838<ref>{{Cite journal| doi = 10.1093/mnras/4.17.152| last = Bessel | first = F. W. | author-link = Friedrich Bessel| title = On the parallax of 61 Cygni| journal = Monthly Notices of the Royal Astronomical Society| volume = 4| issue = 17| pages = 152–161| year = 1838| bibcode = 1838MNRAS...4..152B| doi-access = free}}</ref><ref>{{Cite journal | last = Bessel | first = F. W. | author-link = Friedrich Bessel | doi = 10.1002/asna.18390160502 | title = Bestimmung der Entfernung des 61sten Sterns des Schwans | language = de | trans-title = Determination of the distance to 61 Cygni | journal = Astronomische Nachrichten | volume = 16 | issue = 365–366 | pages = 65–96 | year = 1838 | bibcode = 1838AN.....16...65B | url = https://zenodo.org/record/1424605 | access-date = 2 July 2019 | archive-date = 22 January 2021 | archive-url = https://web.archive.org/web/20210122170129/https://zenodo.org/record/1424605 | url-status = live }}</ref> with a value of 369.0 ±19.1&nbsp;mas to ''A'' and 260.5 ±18.8 to ''B'', and estimated the center point to be at 313.6 ±13.6. This corresponds to a distance of about 600,000 [[astronomical unit]]s, or about 10.4 light-years. This was the first direct and reliable measurement of the distance to a star other than the Sun.<ref name="hopkins-1916" /><ref>{{cite web
 |author      = Frommert, Hartmut
 |author2     = Kronberg, Christine
 |title       = Friedrich Wilhelm Bessel
 |publisher   = Students for the Exploration and Development of Space
 |url         = http://messier.seds.org/xtra/Bios/bessel.html
 |access-date  = 3 April 2009
 |archive-url  = https://web.archive.org/web/20120204150631/http://messier.seds.org/xtra/Bios/bessel.html
 |archive-date = 4 February 2012
}}</ref> His measurement was published only shortly before similar parallax measurements of [[Vega]] by [[Friedrich Georg Wilhelm von Struve]] and [[Alpha Centauri]] by [[Thomas Henderson (astronomer)|Thomas Henderson]] that same year.<ref>{{cite book |first=Stefan |last=Hughes |title=Catchers of the Light |url=https://books.google.com/books?id=iZk5OOf7fVYC&pg=PA702 |page=702 |publisher=ArtDeCiel Publishing |date=2012 |isbn=978-1-62050-961-6}}</ref> Bessel continued to make additional measurements at Königsberg, publishing a total of four complete observational runs, the last in 1868. The best of these placed the center point at 360.2 ±12.1&nbsp;mas, made during observations in 1849.<ref name="hopkins-1916" /> This is close to the currently accepted value of 287.18&nbsp;mas (yielding 11.36&nbsp;light-years).<ref>{{cite journal
 | last=Bessel
 | first=F. W.
 | title=Bestimmung der Entfernung des 61sten Sterns des Schwans. Von Herrn Geheimen – Rath und Ritter Bessel
 | trans-title=Determining the distance of the 61st star of Cygnus. From Mr Geheimen, Rath and Ritter Bessel
 | journal=Astronomische Nachrichten
 | date=1839
 | volume=16
 | issue=5–6
 | pages=65–96
 | language=de
 | bibcode=1838AN.....16...65B
 | quote=(page 92) Ich bin daher der Meinung, daß nur die jährliche Parallaxe = 0"3136 als das Resultat der bisherigen Beobachtungen zu betrachten ist
 | doi=10.1002/asna.18390160502
 | url=https://zenodo.org/record/1424605
 | access-date=2 July 2019
 | archive-date=22 January 2021
 | archive-url=https://web.archive.org/web/20210122170129/https://zenodo.org/record/1424605
 | url-status=live
 }}</ref>

Only a few years after Bessel's measurement, in 1842 [[Friedrich Wilhelm Argelander]] noted that [[Groombridge 1830]] had an even larger proper motion, and 61 Cygni became the second highest known. It was later moved further down the list by [[Kapteyn's Star]] and [[Barnard's Star]]. 61 Cygni has the sixth highest proper motion of all stellar systems listed in the modern [[Hipparcos Catalogue]], but retains the title of highest proper motion among stars visible to the naked eye.<ref name=":1" />