Universe Guide

Tau9 Eridani (36 Eridani) Star Facts

Tau9 Eridani Facts

  • Tau9 Eridani is a rotating variable star that can be located in the constellation of Eridanus. The description is based on the spectral class.
  • Tau9 Eridani is a main star of the constellation outline.
  • Based on the spectral type (Ap Si) 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 327.47 light years away from us. Distance

Tau9 Eridani's Alternative Names

Tau9 Eridani (Tau09 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 HR1240. 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.

Tau9 Eridani has alternative name(s) :- , tau09 Eri.

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 36 Eridani. The Flamsteed name can be shortened to 36 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 161 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 2022.

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

Location of Tau9 Eridani

The location of the variable 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 Tau9 Eridani, the location is 03h 59m 55.48 and -24° 00` 58.5 .

Radial Velocity and Proper Motion of Tau9 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 16.48 ± 0.14 milliarcseconds/year towards the north and 12.12 ± 0.22 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 25.50000 km/s with an error of about 0.50 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 Tau9 Eridani

Tau9 Eridani Colour and Temperature

Based on the star's spectral type of Ap Si , Tau9 Eridani's colour and type is blue - white variable star. The star has a B-V Colour Index of -0.12 which means the star's temperature is about 14,942 Kelvin. The temperature was calculated using information from Morgans @ Uni.edu.

Tau9 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 264.59 that I have given is based on the value in the Simbad Hipparcos Extended Catalogue at the University of Strasbourg from 2012.

Tau9 Eridani Radius

Tau9 Eridani estimated radius has been calculated as being 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. 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 1.6675918751967013297093511924. 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.

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 9.85000 which gave the calculated distance to Tau9 Eridani as 331.13 light years away from Earth or 101.52 parsecs. If you want that in miles, it is about 1,946,589,219,822,288.78, based on 1 Ly = 5,878,625,373,183.61 miles.

In 2007, Hipparcos data was revised with a new parallax of 9.96000 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.

Using the 2007 distance, the star is roughly 20,708,842.25 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 7,452.00 Parsecs or 24,305.69 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 Tau9 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)
Airbus A380736298,378,841.71
Speed of Sound (Mach 1)767.269286,218,819.60
Concorde (Mach 2)1,534.54143,109,223.28
New Horizons Probe33,0006,654,752.35
Speed of Light670,616,629.00327.47

Variable Type of Tau9 Eridani

The star is a rotating Alpha2 Canum Venatic 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 4.605 to a magnitude of 4.578 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 1.2 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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Additional Tau9 Eridani Facts and Figures

Visual Facts

Primary / Proper / Traditional NameTau9 Eridani
Alternative NamesTau09 Eri, HD 25267, HIP 18673, HR 1240, 161 G. Eridani, 36 Eridani, 36 Eri, CD-24 2022, tau09 Eri
Spectral TypeAp Si
Constellation's Main StarYes
Multiple Star SystemYes
Star TypeVariable Star
GalaxyMilky Way
Absolute Magnitude -0.41 / -0.39
Visual / Apparent Magnitude4.62
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)03h 59m 55.48
Declination (Dec.)-24° 00` 58.5
Galactic Latitude-47.62459213 degrees
Galactic Longitude219.64697959 degrees
1997 Distance from Earth9.85000 Parallax (milliarcseconds)
 331.13 Light Years
 101.52 Parsecs
2007 Distance from Earth9.96000 Parallax (milliarcseconds)
 327.47 Light Years
 100.40 Parsecs
 20,708,842.25 Astronomical Units
Galacto-Centric Distance24,305.69 Light Years / 7,452.00 Parsecs
Proper Motion Dec.16.48000 ± 0.14000 milliarcseconds/year
Proper Motion RA.12.12000 ± 0.22000 milliarcseconds/year
B-V Index-0.12
Radial Velocity25.50000 ± 0.50 km/s
Semi-Major Axis7877.0000000
Stellar Luminosity (Lsun)264.5900000
Associated / Clustered StarsTau1 Eridani
Tau3 Eridani
Tau4 Eridani
Tau5 Eridani
Tau6 Eridani
Tau7 Eridani
Tau8 Eridani

Companions (Multi-Star and Exoplanets) Facts

Exoplanet CountNone/Unaware

Variable Star Details

Variable Star ClassRotating
Variable Star TypeAlpha2 Canum Venatic
Mean Variability Period in Days1.210
Variable Magnitude Range (Brighter - Dimmer)4.578 - 4.605

Estimated Calculated Facts

Radius (x the Sun)1.67
Effective Temperature14,942 Kelvin

Sources and Links

SIMBAD SourceLink

Eridanus Main Stars

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