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Tianguan, Zeta Tauri, 123 Tauri, HD37202, HIP26451, HR1910

Tianguan (Zeta Tauri) Location in Taurus

Tianguan (Zeta Tauri) is a blue eclipsing binary system giant star that can be located in the constellation of Taurus. The description is based on the spectral class. The star can be seen with the naked eye, that is, you don't need a telescope/binoculars to see it.

Tianguan's Alternative Names

Zeta Tauri (Zet Tau) is the Bayer Classification for the star. The Id of the star in the Yale Bright Star Catalogue is HR1910. HIP26451 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD37202.

Tianguan has alternative name(s) :- Zeta Tau, Tien Kwan, zet 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 123 Tauri with it shortened to 123 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+21 908.

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

Location of Tianguan

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 Tianguan, the location is 05h 37m 38.68 and +21° 08` 33.3 .

Proper Motion of Tianguan

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 -20.07 ± 0.50 miliarcseconds/year towards the north and 1.78 ± 0.82 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 us is 20.00000 km/s with an error of about 2.50 km/s .

Tianguan 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 2,547.09 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 Tianguan

Tianguan has a spectral type of B4IIIp. This means the star is a blue giant star. The star is 7,533.00 Parsecs from the Galactic Centre or terms of Light Years is 24,569.88 s. The star has a B-V Colour Index of -0.14 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 13,196 Kelvin.

Tianguan Radius has been calculated as being 5.81 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 4,041,367.54.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 6.20. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures.

Tianguan Apparent and Absolute Magnitudes

Tianguan has an apparent magnitude of 2.97 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 -2.56 If you used the 2007 Parallax value, you would get an absolute magnitude of -2.70. 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 Tianguan

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 7.82 which gave the calculated distance to Tianguan as 417.09 light years away from Earth or 127.88 parsecs. It would take a spaceship travelling at the speed of light, 417.09 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 7.33 which put Tianguan at a distance of 444.97 light years or 136.43 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 7,533.00 Parsecs or 24,569.88 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 Tianguan

The star is a eclipsing binary system Eclipsing 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. This is a some uncertainty as to the type but the type mentioned is the current variable star classification for this star. Tianguan brightness ranges from a magnitude of 2.983 to a magnitude of 2.853 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 0.1 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.

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Tianguan Facts

Visual Facts


Primary / Proper / Traditional NameTianguan
Alternative NamesZeta Tauri, Zet Tau, Zeta Tau, Tien Kwan, HD 37202, HIP 26451, HR 1910, 123 Tauri, 123 Tau, BD+21 908, zet Tau
Spectral TypeB4IIIp
Multiple Star SystemNo / Unknown
Star TypeGiant Star
Colour blue
GalaxyMilky Way
ConstellationTaurus
Absolute Magnitude-2.56 / -2.70
Visual / Apparent Magnitude2.97
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)05h 37m 38.68
Declination (Dec.)+21° 08` 33.3
Galactic Latitude-5.64 degrees
Galactic Longitude185.69 degrees
1997 Distance from Earth7.82 Parallax (milliarcseconds)
 417.09 Light Years
 127.88 Parsecs
2007 Distance from Earth7.33 Parallax (milliarcseconds)
 444.97 Light Years
 136.43 Parsecs
Galacto-Centric Distance24,569.88 Light Years / 7,533.00 Parsecs
Proper Motion Dec.-20.07 ± 0.50 milliarcseconds/year
Proper Motion RA.1.78 ± 0.82 milliarcseconds/year
B-V Index-0.14
Radial Velocity20.00 ± 2.50 km/s
Eccentricity0.04
Semi-Major Axis7768.00
Stellar Luminosity (Lsun)2,547.09

Companions (Multi-Star and Exoplanets) Facts


Exoplanet CountNone/Unaware

Variable Star Details


Variable Star ClassEclipsing binary system
Variable Star TypeEclipsing probably
Mean Variability Period in Days0.126
Variable Magnitude Range (Brighter - Dimmer)2.853 - 2.983

Estimated Facts


Calculated Effective Temperature13,196 Kelvin

Sources and Links


SIMBAD SourceLink

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