| absmag_v = 0.74[11]
}}{{Starbox detail
| source = [7]
| mass = 1.59[13]
| radius = 11
| luminosity = 52.5
| temperature = {{Val|4783|20|fmt=commas}}[13]
| gravity = 2.7
| metal_fe = −0.09
| rotational_velocity = 2.2
| age_gyr = 3.29[13]
}}{{Starbox catalog
| names = η Cyg, 21 Cygni, BD+34° 3798, FK5 1521, HD 188947, HIP 98110, HR 7615, SAO 69116.[16]
}}{{Starbox reference
| Simbad = eta+Cygni
}}{{Starbox end}}Eta Cygni (η Cygni) is a star in the northern constellation of Cygnus. It is visible to the naked eye with an apparent visual magnitude of 3.889.[3] The star lies along the main body of the constellation, about midway between Gamma Cygni and Albireo.[18] Based upon an annual parallax shift of 24.17 mas,[ it is located 135 light years from the Sun.]
At an age of about 3.3[13] billion years, this is an evolved red clump[21] giant star with a stellar classification of K0 III.[4] It is presently on the horizontal branch and is generating energy through the nuclear fusion of helium at its core. The star has about 1.59[13] times the mass of the Sun and has expanded to 11[7] It radiates 52.5 times the solar luminosity from its outer atmosphere at an effective temperature of 4,783 K.[13]
Eta Cygni has five visual companions,[26] of which only component B appears to be physically associated. This magnitude 12.0 star lies at an angular separation of 7.80 arc seconds along a position angle of 206°, as of 2007.[27]
References
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9. ^1 2 3 4 {{citation | last1=Oja | first1=T. | title=UBV photometry of stars whose positions are accurately known. III | journal=Astronomy and Astrophysics Supplement Series | volume=65 | issue=2 | pages=405–409 | date=August 1986 | bibcode=1986A&AS...65..405O | postscript=. }}
10. ^1 {{cite simbad | title=eta Cyg | accessdate=2017-02-19 | postscript=. }}