Alrediph (Delta Cephei) is a white to yellow pulsating very luminous supergiant star that can be located in the constellation of Cepheus. Delta Cephei is the Bayer Classification for the star. 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), 27 Cephei , del_Cep, 27 Cep.
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 +58d24`54.7 .
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 003.52 ± 000.12 towards the north and 015.35 ± 000.16 east if we saw them in the horizon.
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.
Alrediph has a spectral type of G2Ibvar. This means the star is a white to yellow supergiant star. 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 has been calculated as 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.
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.
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 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 5.000 to a magnitude of 4.000 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 5.0 days (variability).
|Short Name||del Cep, 27 Cep|
|Bayer Designation||Delta Cephei|
|Alternative Name(s)||27 Cephei|
|Hipparcos Library I.D.||110991|
|Bonner Durchmusterung||BD+57 2548|
|Henry Draper Designation||213306|
|Star Type||supergiant star|
|Absolute Magnitude||-3.32 / -3.05|
|Right Ascension (R.A.)||22h 29m 10.25|
|1997 Distance from Earth||3.32 Parallax (milliarcseconds)|
|982.42 Light Years|
|2007 Revised Distance from Earth||3.77 Parallax (milliarcseconds)|
|865.15 Light Years|
|Proper Motion Dec.||3.52 ± 0.12 milliarcseconds/year|
|Proper Motion RA.||15.35 ± 0.16 milliarcseconds/year|
|Colour||(G) White to Yellow|
|Variable Star Class||Pulsating|
|Variable Star Type||Delta Cepheid|
|Mean Variability Period in Days||5.000|
|Variable Magnitude Range (Brighter - Dimmer)||4.000 - 5.000|
|Radius (x the Sun)||47.62|
|Luminosity (x the Sun)||9,500.0000000|
|Calculated Effective Temperature||5,490 Kelvin|
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. Id||B.D. Id||Star Code||Magnitude||R.A.||Dec.||Spectrum||Colour||Year|