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20 Eridani - HD22470 - HIP16803

20 Eridani is a blue rotating giant star that can be located in the constellation of Eridanus. HIP16803 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD22470. The Id of the star in the Gould Star Catalogue is 107. 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. 20 Eridani has alternative name(s), 20 Eridani , EG_Eri, 20 Eri. 20 Eridani is a multiple star system with 2 stars orbiting in its solar system.

Location of 20 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 20 Eridani, the location is 03h 36m 17.39 and -17d28`01.3 .

Proper Motion of 20 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 -010.91 ± 000.36 towards the north and 032.37 ± 000.51 east if we saw them in the horizon.

Physical Properties (Colour, Temperature, Radius) of 20 Eridani

20 Eridani has a spectral type of B8/B9III. This means the star is a blue giant star. The star has a B-V Colour Index of -0.11 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 12,006 Kelvin.

20 Eridani has been calculated as 2.81 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 1,952,525.65.km.

20 Eridani Apparent and Absolute Magnitudes

20 Eridani has an apparent magnitude of 5.24 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 -0.57 If you used the 2007 Parallax value, you would get an absolute magnitude of -0.63. 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 20 Eridani

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 6.89 which gave the calculated distance to 20 Eridani as 473.39 light years away from Earth or 145.14 parsecs. It would take a spaceship travelling at the speed of light, 473.39 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 6.70 which put 20 Eridani at a distance of 486.81 light years or 149.25 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 20 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. 20 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 2.0 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.

20 Eridani Facts

Alternative Names

Traditional Name20 Eridani
Short NameEG Eri, 20 Eri
Alternative Name(s)20 Eridani
Hipparcos Library I.D.16803
Bonner DurchmusterungBD-17 699
Gould I.D.107
Henry Draper Designation22470

Visual Facts

Star Typegiant star
Absolute Magnitude-0.57 / -0.63
Apparent Magnitude5.24
Right Ascension (R.A.)03h 36m 17.39
Declination (Dec.)-17d28`01.3
1997 Distance from Earth6.89 Parallax (milliarcseconds)
 473.39 Light Years
 145.14 Parsecs
2007 Revised Distance from Earth6.70 Parallax (milliarcseconds)
 486.81 Light Years
 149.25 Parsecs
Proper Motion Dec.-10.91 ± 0.36 milliarcseconds/year
Proper Motion RA.32.37 ± 0.51 milliarcseconds/year
B-V Index-0.11
Spectral TypeB8/B9III
Colour(B) blue
Stars in Solar System2

Variable Star Details

Variable Star ClassRotating
Variable Star TypeAlpha2 Canum Venaticorum
Mean Variability Period in Days2.000

Estimated Facts

Radius (x the Sun)2.81
Calculated Effective Temperature12,006 Kelvin

Sources and Links

SIMBAD SourceLink

Related Stars

Multi-Star System

The star has been identified as being a multi-star system, one in which there is at least one star in close orbit to another star or two or more stars orbiting a central point. The stars may be of equal mass, unequal mass where one star is stronger than the other or be in groups orbiting a central point which doesn't necessarily have to be a star. More information can be found on my dedicated multiple star systems page. The source of the info is Simbad. The file is dated 2000 so any differences between this and any other source will be down to the actual source from where the information came from.


Proper Motion mas/yr
H.D. IdB.D. IdStar CodeMagnitudeR.A.Dec.SpectrumColourYear
22470-17 699.0A5.5000033.00000-10.00000B8Blue/White
B6.8000033.00000-10.000001991

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