to be at 313.6±13.6. This corresponds to a distance of about 600,000 astronomical units, or about 10.4 light-years. This was the first direct and reliable measurement of the distance to a star other than the Sun. His measurement was published only shortly before similar parallax measurements of Vega by Friedrich Georg Wilhelm von Struve and Alpha Centauri by Thomas Henderson that same year. 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 mas, made during observations in 1849. This is close to the currently accepted value of 287.18 mas (yielding 11.36 light-years). 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 seventh 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. Binary observations Due to the wide angular separation between 61 Cygni A and B, and the correspondingly slow orbital motion, it was initially unclear whether the two stars in the 61 Cygni system were a gravitationally bound system or simply a juxtaposition of stars. von Struve first argued for its status as a binary in 1830, but the matter remained open. However, by 1917 refined measured parallax differences demonstrated that the separation was significantly less. The binary nature of this system was clear by 1934, and orbital elements were published. In 1911, Benjamin Boss published data indicating that the 61 Cygni system was a member of a comoving group of stars. This group containing 61 Cygni was later expanded to include 26 potential members. Possible members include Beta Columbae, Pi Mensae, 14 Tauri and 68 Virginis. The space velocities of this group of stars range from 105 to 114 km/s relative to the Sun. Observations taken by planet search programs show that both components have strong linear trends in the radial velocity measurements. Amateur observation An observer using 7×50 binoculars can find 61 Cygni two binocular fields southeast of the bright star Deneb. The angular separation of the two stars is slightly greater than the angular size of Saturn