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Tau9 Eridani - HD25267 - HIP18673

Tau9 Eridani is a blue rotating star that can be located in the constellation of Eridanus. Tau9 Eridani is the Bayer Classification for the star. HIP18673 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD25267. The Id of the star in the Gould Star Catalogue is 161. Stars in the southern hemisphere are more likely to have a Gould Id than the northern hemisphere. For example, there are no Gould classified stars in Ursa Major. Tau9 Eridani has alternative name(s), 36 Eridani , tau09_Eri, 36 Eri.

Location of Tau9 Eridani

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 Tau9 Eridani, the location is 03h 59m 55.48 and -24d00`58.5 .

Proper Motion of Tau9 Eridani

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 016.48 ± 000.14 towards the north and 012.12 ± 000.22 east if we saw them in the horizon.

Physical Properties (Colour, Temperature, Radius) of Tau9 Eridani

Tau9 Eridani has a spectral type of Ap Si. This means the star is a blue star. The star has a B-V Colour Index of -0.12 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 14,942 Kelvin.

Tau9 Eridani has been calculated as 1.68 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 1,171,047.18.km.

Tau9 Eridani Apparent and Absolute Magnitudes

Tau9 Eridani has an apparent magnitude of 4.62 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 -0.41 If you used the 2007 Parallax value, you would get an absolute magnitude of -0.39. 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 Tau9 Eridani

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 9.85 which gave the calculated distance to Tau9 Eridani as 331.13 light years away from Earth or 101.52 parsecs. It would take a spaceship travelling at the speed of light, 331.13 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 9.96 which put Tau9 Eridani at a distance of 327.47 light years or 100.40 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.

Variable Type of Tau9 Eridani

The star is a rotating Alpha2 Canum Venaticorum 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. Tau9 Eridani brightness ranges from a magnitude of 5.000 to a magnitude of 5.000 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 1.0 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 Stellar Age, Metallicity or Mass is from the E.U. Exoplanets. The information was obtained as of 12th Feb 2017.

Tau9 Eridani Facts

Alternative Names

Short Nametau09 Eri, 36 Eri
Bayer DesignationTau9 Eridani
Alternative Name(s)36 Eridani
Hipparcos Library I.D.18673
Gould I.D.161
Henry Draper Designation25267

Visual Facts

Star Type star
Absolute Magnitude-0.41 / -0.39
Apparent Magnitude4.62
Right Ascension (R.A.)03h 59m 55.48
Declination (Dec.)-24d00`58.5
1997 Distance from Earth9.85 Parallax (milliarcseconds)
 331.13 Light Years
 101.52 Parsecs
2007 Revised Distance from Earth9.96 Parallax (milliarcseconds)
 327.47 Light Years
 100.40 Parsecs
Proper Motion Dec.16.48 ± 0.14 milliarcseconds/year
Proper Motion RA.12.12 ± 0.22 milliarcseconds/year
B-V Index-0.12
Spectral TypeAp Si
Colour(A) blue

Variable Star Details

Variable Star ClassRotating
Variable Star TypeAlpha2 Canum Venaticorum
Mean Variability Period in Days1.000

Estimated Facts

Radius (x the Sun)1.68
Calculated Effective Temperature14,942 Kelvin

Sources and Links

SIMBAD SourceLink

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