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Alfirk (Beta Cephei) - HD205021 - HIP106032 - HR8238

Alfirk (Beta Cephei) is a blue pulsating giant star that can be located in the constellation of Cepheus. The star can be seen with the naked eye, that is, you don't need a telescope/binoculars to see it.

Beta Cephei is the Bayer Classification for the star. The Id of the star in the Yale Bright Star Catalogue is HR8238. HIP106032 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD205021.

Alfirk has alternative name(s), 8 Cephei , bet_Cep, 8 Cep. Alfirk has at least 1 Extrasolar Planets believed to be in orbit around the star.

Location of Alfirk

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 Alfirk, the location is 21h 28m 39.58 and +70d33`38.5 .

Proper Motion of Alfirk

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 8.39 ± 0.26 miliarcseconds/year towards the north and 12.54 ± 0.30 miliarcseconds/year east if we saw them in the horizon.

Physical Properties (Colour, Temperature, Radius) of Alfirk

Alfirk has a spectral type of B2IIIv SB. This means the star is a blue giant star. The star is 7464.00000000 Parsecs from the Galactic Centre or terms of Light Years is 24344.8319961600000000s. The star has a B-V Colour Index of -0.2 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 16,954 Kelvin.

Alfirk Radius has been calculated as being 4.47 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 3,110,811.61.km. However with the 2007 release of updated Hipparcos files, the radius is now calculated at being round 5.13. 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 -0.01 with an error value of 9.99 Fe/H with the Sun has a value of 1 to put it into context.

Alfirk Apparent and Absolute Magnitudes

Alfirk has an apparent magnitude of 3.23 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 -3.08 If you used the 2007 Parallax value, you would get an absolute magnitude of -3.38. 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 Alfirk

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 5.48 which gave the calculated distance to Alfirk as 595.19 light years away from Earth or 182.48 parsecs. It would take a spaceship travelling at the speed of light, 595.19 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 4.76 which put Alfirk at a distance of 685.22 light years or 210.08 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 7,464.00 Parsecs or 24,344.83 Light Years. The Galacto-Centric Distance is the distance from the star to the Centre of the Galaxy which is Sagittarius A*.

Variable Type of Alfirk

The star is a pulsating Beta Cephei 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. Alfirk brightness ranges from a magnitude of 3.000 to a magnitude of 3.000 over its variable period. The smaller the magnitude, the brighter the star.

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.

Alfirk Facts

Alternative Names

Traditional/Proper NameAlfirk
Short Namebet Cep, 8 Cep
Bayer DesignationBeta Cephei
Alternative Name(s)8 Cephei
Hipparcos Library I.D.106032
Yale Bright Star Catalogue (HR) Id8238
Bonner DurchmusterungBDD+69 1173
Henry Draper Designation205021

Visual Facts

Star Typegiant star
Absolute Magnitude-3.08 / -3.38
Visual / Apparent Magnitude3.23
Naked Eye VisibleYes - Ref: Wiki
Right Ascension (R.A.)21h 28m 39.58
Declination (Dec.)+70d33`38.5
Galactic Latitude14.03 degrees
Galactic Longitude107.54 degrees
1997 Distance from Earth5.48 Parallax (milliarcseconds)
 595.19 Light Years
 182.48 Parsecs
2007 Revised Distance from Earth4.76 Parallax (milliarcseconds)
 685.22 Light Years
 210.08 Parsecs
Galacto-Centric Distance24,344.83 Light Years / 7,464.00 Parsecs
Proper Motion Dec.8.39 ± 0.26 milliarcseconds/year
Proper Motion RA.12.54 ± 0.30 milliarcseconds/year
B-V Index-0.20
Radial Velocity-3.10 ± 10.00 km/s
Iron Abundance-0.01 ± 9.99 Fe/H
Spectral TypeB2IIIv SB
Colour(B) blue

Companions (Multi-Star and Exoplanets) Facts

Exoplanet Count1

Variable Star Details

Variable Star ClassPulsating
Variable Star TypeBeta Cephei

Estimated Facts

Calculated Effective Temperature16,954 Kelvin

Sources and Links

SIMBAD SourceLink

Related Stars

Multi-Star System

The star has been identified as being a multi-star system, one in which there is at least one star in close orbit to another star or two or more stars orbiting a central point. The stars may be of equal mass, unequal mass where one star is stronger than the other or be in groups orbiting a central point which doesn't necessarily have to be a star. More information can be found on my dedicated multiple star systems page. The source of the info is Simbad. The file is dated 2000 so any differences between this and any other source will be down to the actual source from where the information came from.


Proper Motion mas/yr
H.D. IdB.D. IdStar CodeMagnitudeR.A.Dec.SpectrumColourYear
205021+69 1173.0A3.3000010.0000013.00000B1Blue/White
B8.000001832
P1971

Location of Alfirk in Cepheus


Alfirk (Beta Cephei) Location in Cepheus

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


List of Extrasolar Planets orbiting Alfirk


NameStatusMass (Jupiters)Orbital Period (Days)EccentricityDiscoveredSemi-Major AxisPeriastronInclination
Gamma Cephei BConfirmed11.1903.3000.04920032.0595.00010.000

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