61 Cygni

61 Cygni A61 Cyg61 Cyg B61 Cyg A
61 Cygni is a binary star system in the constellation Cygnus, consisting of a pair of K-type dwarf stars that orbit each other in a period of about 659 years.wikipedia
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Stellar parallax

parallax shiftparallaxparallax method
In 1838, Friedrich Bessel measured its distance from Earth at about 10.4 light-years, very close to the actual value of about 11.4 light-years; this was the first distance estimate for any star other than the Sun, and first star to have its stellar parallax measured.
It was first observed in 1806 by Giuseppe Calandrelli who reported parallax in α-Lyrae in his work "Osservazione e riflessione sulla parallasse annua dall’alfa della Lira". Then in 1838 Friedrich Bessel made the first successful parallax measurement ever, for the star 61 Cygni, using a Fraunhofer heliometer at Königsberg Observatory.

Parallax

solar parallaxmotion parallaxtrigonometric parallax
His observations led to the conclusion that binary stars were separated enough that they would show different movements in parallax over the year, and hoped to use this as a way to measure the distance to the stars.
The first successful measurements of stellar parallax were made by Friedrich Bessel in 1838 for the star 61 Cygni using a heliometer.

Light-year

light yearlight yearsly
In 1838, Friedrich Bessel measured its distance from Earth at about 10.4 light-years, very close to the actual value of about 11.4 light-years; this was the first distance estimate for any star other than the Sun, and first star to have its stellar parallax measured.
The star was 61 Cygni, and he used a 6.2 in heliometer designed by Joseph von Fraunhofer.

Cygnus (constellation)

Cygnusconstellation of CygnusCygnus constellation
61 Cygni is a binary star system in the constellation Cygnus, consisting of a pair of K-type dwarf stars that orbit each other in a period of about 659 years.
61 Cygni is a binary star divisible in large binoculars or a small amateur telescope.

Vega

2828constellation of VegaWhānui
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.
Friedrich Bessel was skeptical about Struve's data, and, when Bessel published a parallax of 0.314″ for the star system 61 Cygni, Struve revised his value for Vega's parallax to nearly double the original estimate.

Giuseppe Piazzi

PiazziG. PiazziPiazzi, G.
61 Cygni first attracted the attention of astronomers when its large proper motion was first demonstrated by Giuseppe Piazzi in 1804.
One of them, 61 Cygni, was specially appointed as a good candidate for measuring a parallax, which was later performed by Friedrich Wilhelm Bessel.

Flamsteed designation

designationFlamsteedFlamsteed numbers
The name "61 Cygni" is part of the Flamsteed designation assigned to stars.
(Flamsteed numbers are generally preferred to Bayer designations with Roman letters.) Examples of well-known stars that are usually referred to by their Flamsteed numbers include 51 Pegasi, and 61 Cygni.

Friedrich Bessel

BesselFriedrich Wilhelm BesselBesselgymnasium
In 1838, Friedrich Bessel measured its distance from Earth at about 10.4 light-years, very close to the actual value of about 11.4 light-years; this was the first distance estimate for any star other than the Sun, and first star to have its stellar parallax measured.
In 1838 Bessel won the race, announcing that 61 Cygni had a parallax of 0.314 arcseconds; which, given the diameter of the Earth's orbit, indicated that the star is 10.3 ly away.

Friedrich Georg Wilhelm von Struve

StruveFriedrich G. W. von StruveFriedrich Struve
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. 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.
He was also the first to measure the parallax of a star Vega, although Friedrich Bessel had been the first to measure the parallax of a star (61 Cygni).

Alpha Centauri

α CentauriAlphaα Centauri A
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.
He withheld his results, however, because he suspected they were too large to be true, but eventually published them in 1839 after Friedrich Wilhelm Bessel released his own accurately determined parallax for 61 Cygni in 1838.

Stellar classification

spectral typeK-typespectral class
61 Cygni is a binary star system in the constellation Cygnus, consisting of a pair of K-type dwarf stars that orbit each other in a period of about 659 years. Although it appears to be a single star to the naked eye, 61 Cygni is in fact a widely separated binary star system, composed of two K class (orange) main sequence stars, the brighter 61 Cygni A and fainter 61 Cygni B, which have apparent magnitudes of 5.2 and 6.1, respectively.
K5V – 61 Cygni A

Binary star

spectroscopic binaryeclipsing binarybinary
61 Cygni is a binary star system in the constellation Cygnus, consisting of a pair of K-type dwarf stars that orbit each other in a period of about 659 years.
Other interesting binaries include 61 Cygni (a binary in the constellation Cygnus, composed of two K class (orange) main-sequence stars, 61 Cygni A and 61 Cygni B, which is known for its large proper motion), Procyon (the brightest star in the constellation Canis Minor and the eighth-brightest star in the night time sky, which is a binary consisting of the main star with a faint white dwarf companion), SS Lacertae (an eclipsing binary which stopped eclipsing), V907 Sco (an eclipsing binary which stopped, restarted, then stopped again) and BG Geminorum (an eclipsing binary which is thought to contain a black hole with a K0 star in orbit around it), 2MASS J18082002-5104378 (a binary in the "thin disk" of the Milky Way, and containing one of the oldest known stars).

BY Draconis variable

BY Dra variableBY DraconisBY Draconis type
61 Cygni A is a typical BY Draconis variable star designated as V1803 Cyg while 61 Cygni B is a flare type variable star named HD 201092 with their magnitudes varying 5.21 V and 6.03, respectively.
Nearby K and M stars that are BY Draconis variables include Barnard's Star, Kapteyn's Star, 61 Cygni, Ross 248, Lacaille 8760, Lalande 21185, and Luyten 726-8.

Thomas Henderson (astronomer)

Thomas HendersonHenderson, ThomasProfessor Thomas Henderson
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.
Henderson did not immediately publish his results, however (there had been previous, discredited attempts to claim a measurement of stellar parallax), and eventually he was beaten to the punch by Friedrich Wilhelm Bessel, who published a parallax of 10.3 light years (9.6% too small) for 61 Cygni in 1838.

Proper motion

proper motionsproper-motionhigh proper motion star
61 Cygni first attracted the attention of astronomers when its large proper motion was first demonstrated by Giuseppe Piazzi in 1804.

K-type main-sequence star

orange dwarfKK-type star
61 Cygni A's long-term stability led to it being selected as an "anchor star" in the Morgan–Keenan (MK) classification system in 1943, serving as the K5 V "anchor point" since that time.
The "anchor points" of the MK classification system among the K-type main-sequence dwarf stars, i.e. those standard stars that have remain unchanged over the years, are Epsilon Eridani (K2 V), and 61 Cygni A (K5 V). Other primary MK standard stars include 70 Ophiuchi A (K0 V), 107 Piscium (K1 V), HD 219134 (K3 V), TW Piscis Austrini (K4 V), HD 120467 (K6 V), 61 Cygni B (K7 V)

Heliometer

heliometers
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.
The first successful measurements of stellar parallax (to determine the distance to a star) were made by Friedrich Bessel in 1838 for the star 61 Cygni using a Fraunhofer heliometer.

Main sequence

main-sequencemain sequence dwarfmain-sequence star
Although it appears to be a single star to the naked eye, 61 Cygni is in fact a widely separated binary star system, composed of two K class (orange) main sequence stars, the brighter 61 Cygni A and fainter 61 Cygni B, which have apparent magnitudes of 5.2 and 6.1, respectively.
style="text-align: left;"|61 Cygni A

Groombridge 1830

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.
When discovered, it had the highest proper motion of any star known, replacing 61 Cygni in that department.

Kaj Aage Gunnar Strand

Kaj Strand
Kaj Strand of the Sproul Observatory, under the direction of Peter van de Kamp, made the first such claim in 1942 using observations to detect tiny but systematic variations in the orbital motions of 61 Cygni A and B. These perturbations suggested that a third body of about 16 Jupiter masses must be orbiting 61 Cygni A. Reports of this third body served as inspiration for Hal Clement's 1953 science fiction novel Mission of Gravity.
Strand is also known for his 1942 and 1957 claims of a planetary system around the nearby star 61 Cygni while working under the direction of Peter van de Kamp at the Sproul Observatory.

Peter van de Kamp

Piet van de Kampvan de Kamp, Petervan de Kamp
Kaj Strand of the Sproul Observatory, under the direction of Peter van de Kamp, made the first such claim in 1942 using observations to detect tiny but systematic variations in the orbital motions of 61 Cygni A and B. These perturbations suggested that a third body of about 16 Jupiter masses must be orbiting 61 Cygni A. Reports of this third body served as inspiration for Hal Clement's 1953 science fiction novel Mission of Gravity.
From the 1940s on Van de Kamp and his staff made similar claims of planetary systems around the nearby stars Lalande 21185, 61 Cygni, and many others, based on the same flawed photographic plates.

1838 in science

1838
Friedrich Wilhelm Bessel makes the first accurate measurement of distance to a star, 61 Cygni, using parallax. Thomas Henderson (Alpha Centauri) and Friedrich Georg Wilhelm Struve (Vega) announce their measurements using parallax shortly afterwards.

List of Foundation universe planets

AnacreonMelpomeniaHaven
The star system 61 Cygni, in the Sirius Sector, is advanced by Lord Dorwin as the potential site for a planet of origin for the human species.