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BC Cygni, HIP100404

BC Cygni is a red pulsating star that can be located in the constellation of Cygnus. The star can not be seen by the naked eye, you need a telescope to see it.

HIP100404 is the reference name for the star in the Hipparcos Star Catalogue.

BC Cygni has alternative name(s), BC Cyg.

BC Cygni is one of the biggest stars that has currently been discovered in the milky way, it is not the largest, that title goes to UY Scuti. We shouldn`t underestimate the size of the star, it is about 856 - 1553 times the size of the radius of the Sun. The radius fluctuates because it is a variable star.

Location of BC Cygni

The location of the star in the galaxy 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 BC Cygni, the location is 20h 21m 38.55 and +37d 31` 59.0 .

Proper Motion of BC Cygni

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 -5.85 ± 0.62 miliarcseconds/year towards the north and -3.64 ± 0.75 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 -3.00000 km/s with an error of about 4.50 km/s .

BC Cygni Luminosity

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 54000.0000000 that I have given is based on the Spectral Types page that I have found on the Internet. You might find a different figure, one that may have been calculated rather than generalised that I have done. The figure is always the amount times the luminosity of the Sun. It is an imprecise figure because of a number of factors including but not limited to whether the star is a variable star and distance.

Physical Properties (Colour, Temperature, Radius) of BC Cygni

BC Cygni has a spectral type of M3.5Ia. This means the star is a red star. The star has a B-V Colour Index of 3.03 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 0 Kelvin. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures.

BC Cygni Apparent and Absolute Magnitudes

BC Cygni has an apparent magnitude of 8.42 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 0.69 If you used the 2007 Parallax value, you would get an absolute magnitude of -1.18. 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.

Distance to BC Cygni

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 2.84 which gave the calculated distance to BC Cygni as 1148.46 light years away from Earth or 352.11 parsecs. It would take a spaceship travelling at the speed of light, 1148.46 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 1.20 which put BC Cygni at a distance of 2718.03 light years or 833.33 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.

Variable Type of BC Cygni

The star is a pulsating Slow 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. BC Cygni brightness ranges from a magnitude of 8.820 to a magnitude of 8.208 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 0.6 days (variability).

Source of Information

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.

BC Cygni Facts

Alternative Names

Traditional/Proper NameBC Cygni
Short NameBC Cyg
Hipparcos Library I.D.100404
Bonner DurchmusterungBD+37 3903

Visual Facts

Star Type star
Absolute Magnitude0.69 / -1.18
Visual / Apparent Magnitude8.42
Naked Eye VisibleRequires a 7x50 Binoculars - Magnitudes
Right Ascension (R.A.)20h 21m 38.55
Declination (Dec.)+37d 31` 59.0
Galactic Latitude0.41 degrees
Galactic Longitude75.85 degrees
1997 Distance from Earth2.84 Parallax (milliarcseconds)
 1148.46 Light Years
 352.11 Parsecs
2007 Revised Distance from Earth1.20 Parallax (milliarcseconds)
 2718.03 Light Years
 833.33 Parsecs
Proper Motion Dec.-5.85 ± 0.62 milliarcseconds/year
Proper Motion RA.-3.64 ± 0.75 milliarcseconds/year
B-V Index3.03
Radial Velocity-3.00 ± 4.50 km/s
Spectral TypeM3.5Ia
Colour(M) Red

Variable Star Details

Variable Star ClassPulsating
Variable Star TypeSlow Irregular
Mean Variability Period in Days0.597
Variable Magnitude Range (Brighter - Dimmer)8.208 - 8.820

Estimated Facts

Luminosity (x the Sun)54,000.0000000

Sources and Links

SIMBAD SourceLink

Related Stars

Location of BC Cygni in Cygnus

BC Cygni Location in Cygnus

The map was generated using Night Vision, an awesome free application by Brian Simpson.

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