Universe Guide


Tau8 Eridani, 33 Eridani, HD24587, HIP18216

Tau8 Eridani is a blue pulsating main sequence dwarf star that can be located in the constellation of Eridanus. Tau8 Eridani is the brightest star in Eridanus based on the Hipparcos 2007 apparent magnitude. The star can be seen with the naked eye, that is, you don't need a telescope/binoculars to see it.

Tau8 Eridani is the Bayer Classification for the star. HIP18216 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD24587. The Id of the star in the Gould Star Catalogue is 149. 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.

Tau8 Eridani has alternative name(s), tau08 Eri.

Location of Tau8 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 Tau8 Eridani, the location is 03h 53m 42.68 and -24d36`44.0 .

Proper Motion of Tau8 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 -7.49 ± 0.20 miliarcseconds/year towards the north and 31.28 ± 0.30 miliarcseconds/year east if we saw them in the horizon.

Tau8 Eridani 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 380.0000000 that I have given is based on the Spectral Types page that I have found on the Internet. You might find a different figure, one that may have been calculated rather than generalised that I have done. The figure is always the amount times the luminosity of the Sun. It is an imprecise figure because of a number of factors including but not limited to whether the star is a variable star and distance.

Physical Properties (Colour, Temperature, Radius) of Tau8 Eridani

Tau8 Eridani has a spectral type of B5V. This means the star is a blue main sequence dwarf star. The star is 7458.00000000 Parsecs from the Galactic Centre or terms of Light Years is 24325.2621955200000000s. The star has a B-V Colour Index of -0.13 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 12,762 Kelvin.

Tau8 Eridani Radius has been calculated as being 2.66 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 1,851,643.68.km. However with the 2007 release of updated Hipparcos files, the radius is now calculated at being round 2.60. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures.

Tau8 Eridani Apparent and Absolute Magnitudes

Tau8 Eridani has an apparent magnitude of 4.64 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 -0.72 If you used the 2007 Parallax value, you would get an absolute magnitude of -0.67. 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 Tau8 Eridani

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 8.46 which gave the calculated distance to Tau8 Eridani as 385.54 light years away from Earth or 118.20 parsecs. It would take a spaceship travelling at the speed of light, 385.54 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 8.65 which put Tau8 Eridani at a distance of 377.07 light years or 115.61 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 7,458.00 Parsecs or 24,325.26 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 Tau8 Eridani

The star is a pulsating Slow Pulsating B- star 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. Tau8 Eridani brightness ranges from a magnitude of 4.603 to a magnitude of 4.585 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 0.9 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.

Tau8 Eridani Facts

Alternative Names

Flamsteed Name33 Eridani
Flamsteed Short Name33 Eri
Short Nametau08 Eri
Bayer DesignationTau8 Eridani
Hipparcos Library I.D.18216
Gould I.D.149
Henry Draper Designation24587

Visual Facts

Star Typemain sequence dwarf star
Absolute Magnitude-0.72 / -0.67
Visual / Apparent Magnitude4.64
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)03h 53m 42.68
Declination (Dec.)-24d36`44.0
Galactic Latitude-49.14 degrees
Galactic Longitude220.00 degrees
1997 Distance from Earth8.46 Parallax (milliarcseconds)
 385.54 Light Years
 118.20 Parsecs
2007 Revised Distance from Earth8.65 Parallax (milliarcseconds)
 377.07 Light Years
 115.61 Parsecs
Galacto-Centric Distance24,325.26 Light Years / 7,458.00 Parsecs
Proper Motion Dec.-7.49 ± 0.20 milliarcseconds/year
Proper Motion RA.31.28 ± 0.30 milliarcseconds/year
B-V Index-0.13
Radial Velocity20.50 ± 0.20 km/s
Spectral TypeB5V
Colour(B) blue

Variable Star Details

Variable Star ClassPulsating
Variable Star TypeSlow Pulsating B- star
Mean Variability Period in Days0.864
Variable Magnitude Range (Brighter - Dimmer)4.585 - 4.603

Estimated Facts

Luminosity (x the Sun)380.0000000
Calculated Effective Temperature12,762 Kelvin

Sources and Links

SIMBAD SourceLink

Related Stars

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