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Tau Cygni, Latinised from Ï„ Cygni, is a 
Tau Cygni is classified as a
binary star
A binary star or binary star system is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved as separate stars us ...
system in the constellation Cygnus, approximately 69 light year
A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distance, astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by t ...
s away from Earth
Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...
. This visual binary system has a period of 49.6 years.
The main star, 4th magnitude GJ 822.1 A, is a yellowish white subgiant
A subgiant is a star that is brighter than a normal main-sequence star of the same spectral class, but not as bright as giant stars. The term subgiant is applied both to a particular spectral luminosity class and to a stage in the evolution ...
star of the spectral type
In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...
F2IV. It therefore has a surface temperature of 6,000 to 7,500 kelvin
The kelvin (symbol: K) is the base unit for temperature in the International System of Units (SI). The Kelvin scale is an absolute temperature scale that starts at the lowest possible temperature (absolute zero), taken to be 0 K. By de ...
s and is larger, hotter, and several times as bright as the Sun
The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...
. Its companion, 6th magnitude GJ 822.1 B, is a yellow main sequence
In astronomy, the main sequence is a classification of stars which appear on plots of stellar color index, color versus absolute magnitude, brightness as a continuous and distinctive band. Stars on this band are known as main-sequence stars or d ...
star of the spectral type G0V. It is similar to the Sun in size, surface temperature, and luminosity.
Tau Cygni is classified as a δ Scuti variable
A Delta Scuti variable (sometimes termed dwarf cepheid when the V-band amplitude is larger than 0.3 mag.) is a class of pulsating star, comprising several sub-classes of object with A- or F-type spectra.
The variables follow a period-luminosity ...
. The magnitude range is given as 3.65 to 3.75, which is the combined magnitude for both components, although the variable component is A.
References
{{Stars of Cygnus Cygnus (constellation) Binary stars Cygni, Tau Delta Scuti variables F-type subgiants G-type main-sequence stars Cygni, 65 104887 202444 BD+37 4240 8130