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Tau3 Eridani (11 Eridani) Star Facts

Tau3 Eridani Facts

  • Tau3 Eridani is a main sequence star that can be located in the constellation of Eridanus. The description is based on the spectral class.
  • Tau3 Eridani is a main star of the constellation outline.
  • Based on the spectral type (A4V) of the star, the star's colour is blue - white .
  • The star can be seen with the naked eye, that is, you don't need a telescope/binoculars to see it.
  • Using the most recent figures given by the 2007 Hipparcos data, the star is 88.63 light years away from us. Distance

Tau3 Eridani's Alternative Names

Tau3 Eridani (Tau03 Eri) is the Bayer Classification for the star. The Bayer Classification was created by Johann Bayer in 1603. The brightest star in the constellation is normally given the Alpha designation, there are exceptions such as Pollux which is Beta Geminorum.

The Id of the star in the Yale Bright Star Catalogue is HR919. HIP14146 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD18978. The Gliese ID of the star is GL 121. The star was part of the original catalogue devised by German Astronomer Wilheim Gliese of stars located within 20 parsecs of Earth. Star Names

Flamsteed designations are named after the creator, Sir John Flamsteed. Sir John named the stars in the constellation with a number and its latin name, this star's Flamsteed designation is 11 Eridani. The Flamsteed name can be shortened to 11 Eri.

The Gould star designation is one that was designed by American astronomer, Benjamin Apthorp Gould. Gould stars are predominantly in the Southern and Equatorial constellations but do appear in northern constellations such as Bootes and Orion. The star has the designation 56 G. Eridani. There are no stars with a Gould designation in Ursa Major for example.

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 CD-24 1387.

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

Location of Tau3 Eridani

The location of the main sequence 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 object is compared to the celestial equator and is expressed in degrees. For Tau3 Eridani, the location is 03h 02m 23.59 and -23° 37` 27.6 .

Radial Velocity and Proper Motion of Tau3 Eridani

Proper Motion

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 -55.28 ± 0.13 milliarcseconds/year towards the north and -147.25 ± 0.18 milliarcseconds/year east if we saw them in the horizon.

Radial Velocity

The Radial Velocity, that is the speed at which the star is moving away/towards the Sun is -9.80000 km/s with an error of about 2.70 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.

Physical Properties of Tau3 Eridani

Tau3 Eridani Colour and Temperature

Based on the star's spectral type of A4V , Tau3 Eridani's colour and type is blue - white main sequence star. The star's effective temperature is 8,045 Kelvin which is hotter than our own Sun's effective Temperature which is 5,777 Kelvin.

Tau3 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 14.38 that I have given is based on the value in the Simbad Hipparcos Extended Catalogue at the University of Strasbourg from 2012.

Tau3 Eridani Radius

Tau3 Eridani estimated radius has been calculated as being 1.95 times bigger than the Sun. The Sun's radius is 695,800km, therefore the star's radius is an estimated 1,359,392.04.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 2.0084493646071158373233346488. The figure is derived at by using the formula from SDSS rather than peer reviewed papers. It has been known to produce widely incorrect figures.

Tau3 Eridani Apparent and Absolute Magnitudes

Tau3 Eridani has an apparent magnitude of 4.08 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 1.97 If you used the 2007 Parallax value, you would get an absolute magnitude of 1.91. 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 Tau3 Eridani

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 37.85000 which gave the calculated distance to Tau3 Eridani as 86.17 light years away from Earth or 26.42 parsecs. If you want that in miles, it is about 506,561,148,407,231.67, based on 1 Ly = 5,878,625,373,183.61 miles.

In 2007, Hipparcos data was revised with a new parallax of 36.80000 which put Tau3 Eridani at a distance of 88.63 light years or 27.17 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 5,604,175.74 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 7,411.00 Parsecs or 24,171.97 Light Years. The Galacto-Centric Distance is the distance from the star to the Centre of the Galaxy which is Sagittarius A*.

Travel Time to Tau3 Eridani

The time it will take to travel to this star is dependent on how fast you are going. U.G. has done some calculations as to how long it will take going at differing speeds. A note about the calculations, when I'm talking about years, I'm talking non-leap years only (365 days).

The New Horizons space probe is the fastest probe that we've sent into space at the time of writing. Its primary mission was to visit Pluto which at the time of launch (2006), Pluto was still a planet.

DescriptionSpeed (m.p.h.)Time (years)
Walking414,859,187,957.07
Car120495,306,265.24
Airbus A38073680,756,456.29
Speed of Sound (Mach 1)767.26977,465,337.23
Concorde (Mach 2)1,534.5438,732,618.13
New Horizons Probe33,0001,801,113.69
Speed of Light670,616,629.0088.63

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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Additional Tau3 Eridani Facts and Figures

Visual Facts


Primary / Proper / Traditional NameTau3 Eridani
Alternative NamesTau03 Eri, HD 18978, HIP 14146, HR 919, 56 G. Eridani, 11 Eridani, 11 Eri, CD-24 1387, Gliese 121
Spectral TypeA4V
Constellation's Main StarYes
Multiple Star SystemYes
Star Type Main Sequence Dwarf Star
ColourBlue
GalaxyMilky Way
ConstellationEridanus
Absolute Magnitude 1.97 / 1.91
Visual / Apparent Magnitude4.08
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)03h 02m 23.59
Declination (Dec.)-23° 37` 27.6
Galactic Latitude-60.29633045 degrees
Galactic Longitude213.53877152 degrees
1997 Distance from Earth37.85000 Parallax (milliarcseconds)
 86.17 Light Years
 26.42 Parsecs
2007 Distance from Earth36.80000 Parallax (milliarcseconds)
 88.63 Light Years
 27.17 Parsecs
 5,604,175.74 Astronomical Units
Galacto-Centric Distance24,171.97 Light Years / 7,411.00 Parsecs
Proper Motion Dec.-55.28000 ± 0.13000 milliarcseconds/year
Proper Motion RA.-147.25000 ± 0.18000 milliarcseconds/year
B-V Index0.16
Radial Velocity-9.80000 ± 2.70 km/s
Eccentricity0.31180
Semi-Major Axis9778.0000000
Stellar Luminosity (Lsun)14.3800000
Associated / Clustered StarsTau1 Eridani
Tau4 Eridani
Tau5 Eridani
Tau6 Eridani
Tau7 Eridani
Tau8 Eridani
Tau9 Eridani

Companions (Multi-Star and Exoplanets) Facts


Exoplanet CountNone/Unaware

Estimated Calculated Facts


Radius (x the Sun)2.01
Effective Temperature8,017 Kelvin

Sources and Links


SIMBAD SourceLink

Eridanus Main Stars


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