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EX Eridani

EX Eridani Facts

EX Eridani's Alternative Names

HIP22192 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD30422.

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 268 G. Eridani. There are no stars with a Gould designation in Ursa Major for example.

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

Location of EX Eridani

The location of the subgiant 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 EX Eridani, the location is 04h 46m 25.75 and -28° 05` 15.0 .

Radial Velocity and Proper Motion of EX 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 17.58 ± 0.25 milliarcseconds/year towards the north and -3.82 ± 0.33 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 14.40 km/s with an error of about 1.00 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.

EX 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 8.86 that I have given is based on the value in the Simbad Hipparcos Extended Catalogue at the University of Strasbourg from 2012.

Physical Properties (Colour, Temperature) of EX Eridani

EX Eridani Colour and Temperature

EX Eridani has a spectral type of A2IV/V. This means the star is a blue - white subgiant star. The star has a B-V Colour Index of 0.18 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 7,889 Kelvin.

EX Eridani Radius

Radius has been calculated as being 1.67 times bigger than the Sun. The Sun's radius is 695,800km, therefore the star's radius is an estimated 1,162,306.19.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 1.63. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures.

EX Eridani Apparent and Absolute Magnitudes

EX Eridani has an apparent magnitude of 6.18 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 2.38 If you used the 2007 Parallax value, you would get an absolute magnitude of 2.43. 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 EX Eridani

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 17.40 which gave the calculated distance to EX Eridani as 187.45 light years away from Earth or 57.47 parsecs. If you want that in miles, it is 1,077,199,313,382,162.86.

In 2007, Hipparcos data was revised with a new parallax of 17.80 which put EX Eridani at a distance of 183.24 light years or 56.18 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 11,587,876.07 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 7,429.00 Parsecs or 24,230.67 Light Years. The Galacto-Centric Distance is the distance from the star to the Centre of the Galaxy which is Sagittarius A*.

Time to Travel to EX Eridani

A note about the calculations, when I'm talking about years, I'm talking non-leap years only (365 days).

If you were to drive there at about 120 m.p.h. in a car with an infinity engine so you didn't have to pull over for petrol, it would take you 9,182,902,718,360.55 hours or 1,048,276,566.02 years.

At the time of writing, the fastest probe so far created is the New Horizon probe which is travelling at a speed of 33,000 m.p.h. If the probe was travelling to EX Eridani then it would take 33,392,373,521.31 hours / 3,811,914.79 years to get there. Speed Ref: N.A.S.A.

It would to take a spaceship journey travelling at the speed of light, 187.45 years to get there. We don't have the technology or spaceship that can carry people over that distance yet.

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 EX Eridani Facts and Figures

Visual Facts


Primary / Proper / Traditional NameEX Eridani
Alternative NamesHD 30422, HIP 22192, 268 G. Eridani
Spectral TypeA2IV/V
Constellation's Main StarNo
Multiple Star SystemNo / Unknown
Star TypeSubgiant Star
ColourBlue
GalaxyMilky Way
ConstellationEridanus
Absolute Magnitude 2.38 / 2.43
Visual / Apparent Magnitude6.18
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)04h 46m 25.75
Declination (Dec.) -28° 05` 15.0
Galactic Latitude-38.47 degrees
Galactic Longitude228.51 degrees
1997 Distance from Earth17.40 Parallax (milliarcseconds)
 187.45 Light Years
 57.47 Parsecs
2007 Distance from Earth17.80 Parallax (milliarcseconds)
 183.24 Light Years
 56.18 Parsecs
 11,587,876.07 Astronomical Units
Galacto-Centric Distance24,230.67 Light Years / 7,429.00 Parsecs
Proper Motion Dec.17.58 ± 0.25 milliarcseconds/year
Proper Motion RA.-3.82 ± 0.33 milliarcseconds/year
B-V Index0.18
Radial Velocity14.40 ± 1.00 km/s
Eccentricity0.10
Semi-Major Axis8172.00
Stellar Luminosity (Lsun)8.86

Companions (Multi-Star and Exoplanets) Facts


Exoplanet CountNone/Unaware

Estimated Calculated Facts


Radius (x the Sun)1.63
Effective Temperature7,889 Kelvin

Sources and Links


SIMBAD SourceLink

Related Stars


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