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Tau1 Hydri - HD10859 - HIP7879

Tau1 Hydri is a white to yellow giant star that can be located in the constellation of Hydrus. The star can be seen with the naked eye, that is, you don't need a telescope/binoculars to see it.

Tau1 Hydri is the Bayer Classification for the star. HIP7879 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD10859. Tau1 Hydri is a multiple star system with 2 stars orbiting in its solar system.

Location of Tau1 Hydri

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 Tau1 Hydri, the location is 01h 41m 21.29 and -79d08`53.7 .

Proper Motion of Tau1 Hydri

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 21.63 ± 0.43 miliarcseconds/year towards the north and 59.29 ± 0.47 miliarcseconds/year east if we saw them in the horizon.

Physical Properties (Colour, Temperature, Radius) of Tau1 Hydri

Tau1 Hydri has a spectral type of G6/G8III. This means the star is a white to yellow giant star. The star is 7353.00000000 Parsecs from the Galactic Centre or terms of Light Years is 23982.7906843200000000s. The star has a B-V Colour Index of 0.94 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 4,968 Kelvin.

Tau1 Hydri Radius has been calculated as being 8.29 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 5,767,873.43.km. However with the 2007 release of updated Hipparcos files, the radius is now calculated at being round 8.25. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures.

Tau1 Hydri Apparent and Absolute Magnitudes

Tau1 Hydri has an apparent magnitude of 6.33 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 0.91 If you used the 2007 Parallax value, you would get an absolute magnitude of 0.92. 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 Tau1 Hydri

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 8.26 which gave the calculated distance to Tau1 Hydri as 394.87 light years away from Earth or 121.07 parsecs. It would take a spaceship travelling at the speed of light, 394.87 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 8.28 which put Tau1 Hydri at a distance of 393.92 light years or 120.77 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 7,353.00 Parsecs or 23,982.79 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.

Tau1 Hydri Facts

Alternative Names

Bayer DesignationTau1 Hydri
Hipparcos Library I.D.7879
Henry Draper Designation10859

Visual Facts

Star Typegiant star
Absolute Magnitude0.91 / 0.92
Visual / Apparent Magnitude6.33
Naked Eye VisibleYes - Ref: Wiki
Right Ascension (R.A.)01h 41m 21.29
Declination (Dec.)-79d08`53.7
Galactic Latitude-37.69 degrees
Galactic Longitude299.98 degrees
1997 Distance from Earth8.26 Parallax (milliarcseconds)
 394.87 Light Years
 121.07 Parsecs
2007 Revised Distance from Earth8.28 Parallax (milliarcseconds)
 393.92 Light Years
 120.77 Parsecs
Galacto-Centric Distance23,982.79 Light Years / 7,353.00 Parsecs
Proper Motion Dec.21.63 ± 0.43 milliarcseconds/year
Proper Motion RA.59.29 ± 0.47 milliarcseconds/year
B-V Index0.94
Radial Velocity2.20 ± 0.40 km/s
Spectral TypeG6/G8III
Colour(G) White to Yellow
Stars in Solar System2

Estimated Facts

Calculated Effective Temperature4,968 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
10859-79 44.4A6.2000054.0000035.00000K0Orange
B12.200001918

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