Sigma Cygni is a blue eruptive supergiant star that can be located in the constellation of Cygnus. The description is based on the spectral class. The star can be seen with the naked eye, that is, you don't need a telescope/binoculars to see it.
Sigma Cygni (Sig Cyg) is the Bayer Classification for the star. The Id of the star in the Yale Bright Star Catalogue is HR8143. HIP105102 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD202850.
Sigma Cygni has alternative name(s) :- , NSV 13640.
Flamsteed designations are named after the creator, Sir John Flamsteed. Sir John numbered the stars in the constellation with a number and the latin name, this star's Flamsteed designation is 67 Cygni with it shortened to 67 Cyg.
BD number is the number that the star was filed under in the Durchmusterung or Bonner Durchmusterung, a star catalogue that was put together by the Bonn Observatory between 1859 to 1903. The star's BD Number is BD+38 4431.
More details on star alternative names can be found at Star Names .
The location of the star in the night sky is determined by the Right Ascension (R.A.) and Declination (Dec.), these are equivalent to the Longitude and Latitude on the Earth. The Right Ascension is how far expressed in time (hh:mm:ss) the star is along the celestial equator. If the R.A. is positive then its eastwards. The Declination is how far north or south the star is compared to the celestial equator and is expressed in degrees. For Sigma Cygni, the location is 21h 17m 24.95 and +39° 23` 40.9 .
All stars like planets orbit round a central spot, in the case of planets, its the central star such as the Sun. In the case of a star, its the galactic centre. The constellations that we see today will be different than they were 50,000 years ago or 50,000 years from now. Proper Motion details the movements of these stars and are measured in milliarcseconds. The star is moving -3.58 ± 0.14 miliarcseconds/year towards the north and -0.13 ± 0.19 miliarcseconds/year east if we saw them in the horizon. The Radial Velocity, that is the speed at which the star is moving away/towards us is -5.30000 km/s with an error of about 0.40 km/s .
Luminosity is the amount of energy that a star pumps out and its relative to the amount that our star, the Sun gives out. The figure of 11,342.16 that I have given is based on the value in the Simbad Hipparcos Extended Catalogue at the University of Strasbourg from 2012.
Sigma Cygni has a spectral type of B9Iab. This means the star is a blue supergiant star. The star is 7,364.00 Parsecs from the Galactic Centre or terms of Light Years is 24,018.67 s. The star has a B-V Colour Index of 0.09 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 8,573 Kelvin.
Sigma Cygni Radius has been calculated as being 84.08 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 58,504,045.55.km. If you need the diameter of the star, you just need to multiple the radius by 2. However with the 2007 release of updated Hipparcos files, the radius is now calculated at being round 53.54. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures. The star's Iron Abundance is 0.15 with an error value of 0.04 Fe/H with the Sun has a value of 1 to put it into context.
Sigma Cygni has an apparent magnitude of 4.22 which is how bright we see the star from Earth. Apparent Magnitude is also known as Visual Magnitude. If you used the 1997 Parallax value, you would get an absolute magnitude of -6.49 If you used the 2007 Parallax value, you would get an absolute magnitude of -5.51. Magnitude, whether it be apparent/visual or absolute magnitude is measured by a number, the smaller the number, the brighter the Star is. Our own Sun is the brightest star and therefore has the lowest of all magnitudes, -26.74. A faint star will have a high number.
Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 0.72 which gave the calculated distance to Sigma Cygni as 4530.05 light years away from Earth or 1388.89 parsecs. It would take a spaceship travelling at the speed of light, 4530.05 years to get there. We don't have the technology or spaceship that can carry people over that distance yet.
In 2007, Hipparcos data was revised with a new parallax of 1.13 which put Sigma Cygni at a distance of 2886.40 light years or 884.96 parsecs. It should not be taken as though the star is moving closer or further away from us. It is purely that the distance was recalculated.
The star's Galacto-Centric Distance is 7,364.00 Parsecs or 24,018.67 Light Years. The Galacto-Centric Distance is the distance from the star to the Centre of the Galaxy which is Sagittarius A*.
The star is a eruptive Irregular variable type which means that its size changes over time. The Variable Type is usually named after the first star of that type to be spotted. Sigma Cygni brightness ranges from a magnitude of 4.306 to a magnitude of 4.245 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 0.1 days (variability).
The source of the information if it has a Hip I.D. is from Simbad, the Hipparcos data library based at the University at Strasbourg, France. Hipparcos was a E.S.A. satellite operation launched in 1989 for four years. The items in red are values that I've calculated so they could well be wrong. Information regarding Metallicity and/or Mass is from the E.U. Exoplanets. The information was obtained as of 12th Feb 2017.
|Primary / Proper / Traditional Name||Sigma Cygni|
|Alternative Names||Sig Cyg, HD 202850, HIP 105102, HR 8143, 67 Cygni, 67 Cyg, BD+38 4431, NSV 13640|
|Multiple Star System||No / Unknown|
|Star Type||very luminous Supergiant Star|
|Absolute Magnitude||-6.49 / -5.51|
|Visual / Apparent Magnitude||4.22|
|Naked Eye Visible||Yes - Magnitudes|
|Right Ascension (R.A.)||21h 17m 24.95|
|Declination (Dec.)||+39° 23` 40.9|
|Galactic Latitude||-6.87 degrees|
|Galactic Longitude||84.19 degrees|
|1997 Distance from Earth||0.72 Parallax (milliarcseconds)|
|4530.05 Light Years|
|2007 Distance from Earth||1.13 Parallax (milliarcseconds)|
|2886.40 Light Years|
|Galacto-Centric Distance||24,018.67 Light Years / 7,364.00 Parsecs|
|Proper Motion Dec.||-3.58 ± 0.14 milliarcseconds/year|
|Proper Motion RA.||-0.13 ± 0.19 milliarcseconds/year|
|Radial Velocity||-5.30 ± 0.40 km/s|
|Iron Abundance||0.15 ± 0.04 Fe/H|
|Stellar Luminosity (Lsun)||11,342.16|
|Variable Star Class||Eruptive|
|Variable Star Type||Irregular|
|Mean Variability Period in Days||0.051|
|Variable Magnitude Range (Brighter - Dimmer)||4.245 - 4.306|
|Calculated Effective Temperature||8,573 Kelvin|