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Prima Hyadum, Gamma Tauri, 54 Tauri, HD27371, HIP20205, HR1346

Prima Hyadum (Gamma Tauri) Location in Taurus

Prima Hyadum (Gamma Tauri) is a white to yellow giant star that can be located in the constellation of Taurus. The description is based on the spectral class. Prima Hyadum is a main star of the constellation.

The star can be seen with the naked eye, that is, you don't need a telescope/binoculars to see it.

Prima Hyadum's Alternative Names

Gamma Tauri (Gam Tau) is the Bayer Classification for the star. The Id of the star in the Yale Bright Star Catalogue is HR1346. HIP20205 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD27371.

Prima Hyadum has alternative name(s) :- Hyadum I, Gamma Tau.

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 54 Tauri with it shortened to 54 Tau.

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+15 612.

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

Location of Prima Hyadum

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 Prima Hyadum, the location is 04h 19m 47.53 and +15° 37` 39.7 .

Radial Velocity and Proper Motion of Prima Hyadum

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 -23.42 ± 0.20 miliarcseconds/year towards the north and 115.46 ± 0.32 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 the Sun is 38.56 km/s with an error of about 0.09 km/s . When the value is negative then the star and the Sun are getting closer to one another, likewise, a positive number means that two stars are moving away. Its nothing to fear as the stars are so far apart, they won't collide in our life-time, if ever.

Prima Hyadum 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 101.36 that I have given is based on the value in the Simbad Hipparcos Extended Catalogue at the University of Strasbourg from 2012.

Physical Properties (Colour, Temperature) of Prima Hyadum

Prima Hyadum has a spectral type of G8III. This means the star is a white to yellow giant star. The star is 7,445.00 Parsecs from the Galactic Centre or terms of Light Years is 24,282.86 s. The star has a B-V Colour Index of 0.98 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 4,888 Kelvin.

Prima Hyadum Radius has been calculated as being 11.45 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 7,963,842.95.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 11.99. 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 0.12 with an error value of 9.99 Fe/H with the Sun has a value of 1 to put it into context.

Prima Hyadum Apparent and Absolute Magnitudes

Prima Hyadum has an apparent magnitude of 3.65 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 0.28 If you used the 2007 Parallax value, you would get an absolute magnitude of 0.18. 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 Prima Hyadum

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 21.17 which gave the calculated distance to Prima Hyadum as 154.07 light years away from Earth or 47.24 parsecs. It would take a spaceship travelling at the speed of light, 154.07 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 20.19 which put Prima Hyadum at a distance of 161.55 light years or 49.53 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.

Using the 2007 distance, the star is roughly 10,216,224.67 Astronomical Units from the Earth/Sun give or take a few. An Astronomical Unit is the distance between Earth and the Sun. The number of A.U. is the number of times that the star is from the Earth compared to the Sun.

The star's Galacto-Centric Distance is 7,445.00 Parsecs or 24,282.86 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.

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Prima Hyadum Facts

Visual Facts


Primary / Proper / Traditional NamePrima Hyadum
Alternative NamesGamma Tauri, Gam Tau, Hyadum I, Gamma Tau, HD 27371, HIP 20205, HR 1346, 54 Tauri, 54 Tau, BD+15 612
Spectral TypeG8III
Constellation's Main StarYes
Multiple Star SystemYes
Star TypeGiant Star
Colour white to yellow
GalaxyMilky Way
ConstellationTaurus
Absolute Magnitude 0.28 / 0.18
Visual / Apparent Magnitude3.65
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)04h 19m 47.53
Declination (Dec.)+15° 37` 39.7
Galactic Latitude-23.82 degrees
Galactic Longitude179.08 degrees
1997 Distance from Earth21.17 Parallax (milliarcseconds)
 154.07 Light Years
 47.24 Parsecs
2007 Distance from Earth20.19 Parallax (milliarcseconds)
 161.55 Light Years
 49.53 Parsecs
 10,216,224.67 Astronomical Units
Galacto-Centric Distance24,282.86 Light Years / 7,445.00 Parsecs
Proper Motion Dec.-23.42 ± 0.20 milliarcseconds/year
Proper Motion RA.115.46 ± 0.32 milliarcseconds/year
B-V Index0.98
Radial Velocity38.56 ± 0.09 km/s
Iron Abundance 0.12 ± 9.99 Fe/H
Eccentricity0.14
Semi-Major Axis7132.00
Stellar Luminosity (Lsun)101.36

Companions (Multi-Star and Exoplanets) Facts


Exoplanet CountNone/Unaware

Estimated Facts


Calculated Effective Temperature4,888 Kelvin

Sources and Links


SIMBAD SourceLink

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
27371+15 612.0A3.60000115.00000-25.00000
B1978

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