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Alcyone (Eta Tauri) - HD23630 - HIP17702 - HR1165

Alcyone (Eta Tauri) is a blue giant star that can be located in the constellation of Taurus. The star can be seen with the naked eye, that is, you don't need a telescope/binoculars to see it.

Eta Tauri is the Bayer Classification for the star. The Id of the star in the Yale Bright Star Catalogue is HR1165. HIP17702 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD23630.

Alcyone has alternative name(s), Eta Tau,25 Tauri , 25 Tau.

Location of Alcyone

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 Alcyone, the location is 03h 47m 29.06 and +24d06`18.9 .

Proper Motion of Alcyone

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 -43.67 ± 0.25 miliarcseconds/year towards the north and 19.34 ± 0.42 miliarcseconds/year east if we saw them in the horizon.

Physical Properties (Colour, Temperature, Radius) of Alcyone

Alcyone has a spectral type of B7III. This means the star is a blue giant star. The star is 7511.00000000 Parsecs from the Galactic Centre or terms of Light Years is 24498.1287678400000000s. The star has a B-V Colour Index of -0.08 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 11,099 Kelvin.

Alcyone Radius has been calculated as being 7.66 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 5,331,430.94.km. However with the 2007 release of updated Hipparcos files, the radius is now calculated at being round 8.40. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures.

Alcyone Apparent and Absolute Magnitudes

Alcyone has an apparent magnitude of 2.85 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 -2.41 If you used the 2007 Parallax value, you would get an absolute magnitude of -2.61. 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 Alcyone

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 8.87 which gave the calculated distance to Alcyone as 367.72 light years away from Earth or 112.74 parsecs. It would take a spaceship travelling at the speed of light, 367.72 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 8.09 which put Alcyone at a distance of 403.17 light years or 123.61 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 7,511.00 Parsecs or 24,498.13 Light Years. The Galacto-Centric Distance is the distance from the star to the Centre of the Galaxy which is Sagittarius A*.

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.

Alcyone Facts

Alternative Names

Traditional/Proper NameAlcyone
Short Name25 Tau
Bayer DesignationEta Tauri
Alternative Name(s)Eta Tau,25 Tauri
Hipparcos Library I.D.17702
Yale Bright Star Catalogue (HR) Id1165
Bonner DurchmusterungBDD+23 541
Henry Draper Designation23630

Visual Facts

Star Typegiant star
Absolute Magnitude-2.41 / -2.61
Visual / Apparent Magnitude2.85
Naked Eye VisibleYes - Ref: Wiki
Right Ascension (R.A.)03h 47m 29.06
Declination (Dec.)+24d06`18.9
Galactic Latitude-23.46 degrees
Galactic Longitude166.67 degrees
1997 Distance from Earth8.87 Parallax (milliarcseconds)
 367.72 Light Years
 112.74 Parsecs
2007 Revised Distance from Earth8.09 Parallax (milliarcseconds)
 403.17 Light Years
 123.61 Parsecs
Galacto-Centric Distance24,498.13 Light Years / 7,511.00 Parsecs
Proper Motion Dec.-43.67 ± 0.25 milliarcseconds/year
Proper Motion RA.19.34 ± 0.42 milliarcseconds/year
B-V Index-0.08
Radial Velocity5.40 ± 1.20 km/s
Spectral TypeB7III
Colour(B) blue

Estimated Facts

Calculated Effective Temperature11,099 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
23630+23 541.0A3.0000020.00000-44.00000B5Blue/White
23629+23 536.0B8.1000032.00000-44.00000A0White1836
23607+23 534.0C8.1000017.00000-41.00000A0White1868
23608+23 531.0D8.7000020.00000-39.00000G0Yellow1868

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