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Alrediph, Delta Cephei, 27 Cephei, HD213306, HIP110991, HR8571

Alrediph (Delta Cephei) is a white to yellow pulsating very luminous supergiant star that can be located in the constellation of Cepheus. Alrediph is the brightest star in Cepheus based on the Hipparcos 2007 apparent magnitude. The star can be seen with the naked eye, that is, you don't need a telescope/binoculars to see it.

Delta Cephei is the Bayer Classification for the star. The Id of the star in the Yale Bright Star Catalogue is HR8571. HIP110991 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD213306.

Alrediph has alternative name(s), del Cep.

Location of Alrediph

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 Alrediph, the location is 22h 29m 10.25 and +58d 24` 54.7 .

Proper Motion of Alrediph

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 3.52 ± 0.12 miliarcseconds/year towards the north and 15.35 ± 0.16 miliarcseconds/year east if we saw them in the horizon.

Alrediph 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 9500.0000000 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 Alrediph

Alrediph has a spectral type of G2Ibvar. This means the star is a white to yellow supergiant star. The star is 7474.00000000 Parsecs from the Galactic Centre or terms of Light Years is 24377.4483305600000000s. The star has a B-V Colour Index of 0.77 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 5,490 Kelvin.

Alrediph Radius has been calculated as being 47.62 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 33,134,142.49.km. However with the 2007 release of updated Hipparcos files, the radius is now calculated at being round 42.05. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures.

Alrediph Apparent and Absolute Magnitudes

Alrediph has an apparent magnitude of 4.07 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 -3.32 If you used the 2007 Parallax value, you would get an absolute magnitude of -3.05. 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 Alrediph

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 3.32 which gave the calculated distance to Alrediph as 982.42 light years away from Earth or 301.20 parsecs. It would take a spaceship travelling at the speed of light, 982.42 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 3.77 which put Alrediph at a distance of 865.15 light years or 265.25 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 7,474.00 Parsecs or 24,377.45 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 Alrediph

The star is a pulsating Delta Cepheid 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. Alrediph brightness ranges from a magnitude of 4.515 to a magnitude of 3.560 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 5.4 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.

Alrediph Facts

Alternative Names

Traditional/Proper NameAlrediph
Flamsteed Name27 Cephei
Flamsteed Short Name27 Cep
Short Namedel Cep
Bayer DesignationDelta Cephei
Hipparcos Library I.D.110991
Yale Bright Star Catalogue (HR) Id8571
Bonner DurchmusterungBD+57 2548
Henry Draper Designation213306

Visual Facts

Star Typesupergiant star
Absolute Magnitude-3.32 / -3.05
Visual / Apparent Magnitude4.07
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)22h 29m 10.25
Declination (Dec.)+58d 24` 54.7
Galactic Latitude0.53 degrees
Galactic Longitude105.19 degrees
1997 Distance from Earth3.32 Parallax (milliarcseconds)
 982.42 Light Years
 301.20 Parsecs
2007 Revised Distance from Earth3.77 Parallax (milliarcseconds)
 865.15 Light Years
 265.25 Parsecs
Galacto-Centric Distance24,377.45 Light Years / 7,474.00 Parsecs
Proper Motion Dec.3.52 ± 0.12 milliarcseconds/year
Proper Motion RA.15.35 ± 0.16 milliarcseconds/year
B-V Index0.77
Radial Velocity-24.00 ± 0.20 km/s
Spectral TypeG2Ibvar
Colour(G) White to Yellow

Variable Star Details

Variable Star ClassPulsating
Variable Star TypeDelta Cepheid
Mean Variability Period in Days5.366
Variable Magnitude Range (Brighter - Dimmer)3.560 - 4.515

Estimated Facts

Luminosity (x the Sun)9,500.0000000
Calculated Effective Temperature5,490 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
213306+57 2548.0A12.000005.00000G0Yellow

Location of Alrediph in Cepheus

Alrediph (Delta Cephei) Location in Cepheus

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

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