61 Cygni

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61 Cygni
61 cygni map.png
Observational Data
Designation 61 Cygni 2
Struve 2758
Right ascension 21h 06m 53.9434s
Declination +38o 44′ 57.898″
Constellation Cygnus
Type of object Binary star
Magnitude Apparent Mag: 6.04 Absolute Mag: 7.48/8.33
Distance from Earth 11.36 ly
Radial velocity -64.3/-63.5 km/s
Proper motion RA: 4156.93/4109.17 mas/yr
Dec.: 3259.39/3144.17mas/yr
Parallax 287.18 ±1.51 mas

61 Cygni, also called 61 Cygni 2, Bessel's Star, or Piazzi's Flying Star, is a binary star system located some 11.4 light years from our solar system in the constellation of Cygnus near the star Deneb. The binary pair has an apparent magnitude of 6.04, making them invisible to the unaided eye except for the darkest and clearest of conditions. Appearing as a single star to the unaided eye, a standard pair of binoculars is enough to resolve the two binary stars individually.


The first important revelation about the star was in 1792 by Giuseppe Piazzi,[1] who demonstrated the star's unusually large proper motion and referred to the system as the Flying Star. Friedrich Georg Wilhelm von Struve was able to measure the star as a binary in 1830. However the star did not become significant in history until 1838, when German mathematician and astronomer Friedrich Wilhelm Bessel calculated its distance using trigonometric parallax, the first celestial object outside our own system to be measured in such a way.[2] The distance he calculated was so enormous, that the distance could best be adequately explained in the amount of years it took light to reach us from the binary pair.

The Stars

Although barely visual to the naked eye and appearing as a single star, 61 Cygni is actually a binary star, each which orbit around a common barycenter only every 659 years. The average distance of the pair from each other is 86 AUs, but the large orbital eccentricity of 0.48 means the stars approach as close as 44 AUs at periastron and are as far apart as 124 AUs at apastron during their mutual orbit.[3]

The system also has a large proper motion due to its velocity of 108 km/s relative to our Solar System. As such, the system is approaching us relatively quickly and will become as close as 9 light years by around 20,000 A.D. before receding.[4]

61 Cygni A

61 Cygni A is an orange-red main sequence dwarf of spectral type K3.5-5.0 Ve, and is the larger and more luminous of the binary pair. The star has 70 percent of our Sun's mass and 72 percent of its diameter.[5][6] As a dimmer K class star though, it has only 8.5 percent the Sun's visual luminosity. 61 Cyngi A also has a lower metallicity, being only 79 percent as enriched as our Sun, based on the abundance of iron detected. The star has also been found to be a variable star, and has the variable designation V1083 Cygni.

61 Cygni B

61 Cygni B, the smaller and dimmer star of the pair, is an orange-red main sequence dwarf of spectral type K4.7-7.0 Ve. The star has 63 percent of our Sun's mass and 67 percent the diameter.[5][6] Slightly more visually red, the dim star has only 3.5 percent of our Sun's visual luminosity. Observations have found dust in orbit around the star. Like its companion, 61 Cygni B is a variable star, with the variable designation NSV 13546.

Planetary Companions

Despite numerous claims, no sub-stellar objects have been independently confirmed as orbiting either star. For an Earth-like world where water could exist in a liquid state, it would need to be centered around 0.39 AU around 61 Cygni A, nearly the same distance as Mercury. For 61 Cygni B, such a world would need to be centered around 0.34 AU.[3]