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P Cygni, 34 Cygni, HD193237, HIP100044, HR7763

P Cygni is a blue eruptive variable 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.

P Cygni's Alternative Names

The Id of the star in the Yale Bright Star Catalogue is HR7763. HIP100044 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD193237.

P Cygni has alternative name(s) :- , P Cyg.

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 34 Cygni with it shortened to 34 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+37 3871.

More details on star alternative names can be found at Star Names .

Location of P Cygni

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 P Cygni, the location is 20h 17m 47.20 and +38° 01` 58.6 .

Proper Motion of P 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 -6.45 ± 0.13 miliarcseconds/year towards the north and -3.18 ± 0.16 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 -8.90000 km/s with an error of about 0.80 km/s .

Physical Properties (Colour, Temperature) of P Cygni

P Cygni has a spectral type of B2pe. This means the star is a blue variable star. The star has a B-V Colour Index of 0.37 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 6,501 Kelvin.

P Cygni Radius has been calculated as being 157.40 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 109,519,835.98.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 255.28. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures.

P Cygni Apparent and Absolute Magnitudes

P Cygni has an apparent magnitude of 4.77 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 -6.65 If you used the 2007 Parallax value, you would get an absolute magnitude of -7.70. 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 P Cygni

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 0.52 which gave the calculated distance to P Cygni as 6272.37 light years away from Earth or 1923.08 parsecs. It would take a spaceship travelling at the speed of light, 6272.37 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 0.32 which put P Cygni at a distance of 10192.60 light years or 3125 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 P Cygni

The star is a eruptive S Doradus. S Doradus is a star in the Large Magellanic Cloud, not the Milky Way 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. P Cygni brightness ranges from a magnitude of 4.963 to a magnitude of 4.780 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 0.2 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.

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P Cygni Facts

Visual Facts


 P Cygni
Alternative NamesP Cyg, HD 193237, HIP 100044, HR 7763, 34 Cygni, 34 Cyg, BD+37 3871, P Cyg
Spectral TypeB2pe
Multiple Star SystemNo / Unknown
Star TypeVariable Star
Colour blue
GalaxyMilky Way
ConstellationCygnus
Absolute Magnitude-6.65 / -7.70
Visual / Apparent Magnitude4.77
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)20h 17m 47.20
Declination (Dec.)+38° 01` 58.6
Galactic Latitude1.32 degrees
Galactic Longitude75.83 degrees
1997 Distance from Earth0.52 Parallax (milliarcseconds)
 6272.37 Light Years
 1923.08 Parsecs
2007 Distance from Earth0.32 Parallax (milliarcseconds)
 10192.60 Light Years
 3125 Parsecs
Proper Motion Dec.-6.45 ± 0.13 milliarcseconds/year
Proper Motion RA.-3.18 ± 0.16 milliarcseconds/year
B-V Index0.37
Radial Velocity-8.90 ± 0.80 km/s

Companions (Multi-Star and Exoplanets) Facts


Exoplanet CountNone/Unaware

Variable Star Details


Variable Star ClassEruptive
Variable Star TypeS Doradus. S Doradus is a star in the Large Magellanic Cloud, not the Milky Way
Mean Variability Period in Days0.156
Variable Magnitude Range (Brighter - Dimmer)4.780 - 4.963

Estimated Facts


Calculated Effective Temperature6,501 Kelvin

Sources and Links


SIMBAD SourceLink

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