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51 Eridani

51 Eridani Facts

  • 51 Eridani is a main sequence star that can be located in the constellation of Eridanus. The description is based on the spectral class.
  • 51 Eridani is not part of the constellation outline but is within the borders of the constellation.
  • Based on the spectral type (F0V) of the star, the star's colour is yellow to white .
  • The star can be seen with the naked eye, that is, you don't need a telescope/binoculars to see it.
  • It is calculated at being .020 Billion Years old. This information comes from ExoPlanet.
  • 51 Eridani has at least 1 Extrasolar Planets believed to be in orbit around the star.
  • Using the most recent figures given by the 2007 Hipparcos data, the star is 95.99 light years away from us. Distance

51 Eridani's Alternative Names

The Id of the star in the Yale Bright Star Catalogue is HR1474. HIP21547 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD29391.

51 Eridani has alternative name(s) :- C Eridani, C 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 51 Eridani. The Flamsteed name can be shortened to 51 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 252 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 BD-02 963.

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

Location of 51 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 51 Eridani, the location is 04h 37m 36.11 and -02° 28` 24.2 .

Radial Velocity and Proper Motion of 51 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 -64.39 ± 0.20 milliarcseconds/year towards the north and 44.22 ± 0.34 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 12.60000 km/s with an error of about 0.30 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 51 Eridani

51 Eridani Temperature and Colour

Based on the star's spectral type of F0V , 51 Eridani's colour and type is yellow to white main sequence star. The star has a B-V Colour Index of 0.28 which means the star's temperature is about 7,322 Kelvin. The temperature was calculated using information from Morgans @ Uni.edu.

51 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 5.85 that I have given is based on the value in the Simbad Hipparcos Extended Catalogue at the University of Strasbourg from 2012.

51 Eridani Radius

51 Eridani estimated radius has been calculated as being 1.56 times bigger than the Sun. The Sun's radius is 695,800km, therefore the star's radius is an estimated 1,086,676.81.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 1.5403367680947944289536080213. 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.

51 Eridani Mass

The 51 Eridani's solar mass is 1.75 times that of our star, the Sun. The Sun's Mass is 1,989,100,000,000,000,000,000 billion kg. which to calculate using this website is too large. To give idea of size, the Sun is 99.86% the mass of the solar system.

51 Eridani Metalicity

The star's metallicity is -0.027000, this value is the fractional amount of the star that is not Hydrogen (X) or Helium (Y). An older star would have a high metallicity whereas a new star would have a lower one.

51 Eridani Estimated Age

The star is believed to be about 0.02 Billion years old. To put in context, the Sun is believed to be about five billion years old and the Universe is about 13.8 billion years old.

51 Eridani Apparent and Absolute Magnitudes

51 Eridani has an apparent magnitude of 5.22 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 2.85 If you used the 2007 Parallax value, you would get an absolute magnitude of 2.88. 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 51 Eridani

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 33.60000 which gave the calculated distance to 51 Eridani as 97.07 light years away from Earth or 29.76 parsecs. If you want that in miles, it is about 570,638,164,974,933.02, based on 1 Ly = 5,878,625,373,183.61 miles.

In 2007, Hipparcos data was revised with a new parallax of 33.98000 which put 51 Eridani at a distance of 95.99 light years or 29.43 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 6,070,330.95 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 7,424.00 Parsecs or 24,214.37 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 51 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)
Walking416,093,122,554.43
Car120536,437,418.48
Airbus A38073687,462,622.58
Speed of Sound (Mach 1)767.26983,898,202.87
Concorde (Mach 2)1,534.5441,949,046.76
New Horizons Probe33,0001,950,681.52
Speed of Light670,616,629.0095.99

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 51 Eridani Facts and Figures

Visual Facts


Primary / Proper / Traditional Name51 Eridani
Alternative NamesC Eri, C Eridani, C Eri, HD 29391, HIP 21547, HR 1474, 252 G. Eridani, 51 Eri, BD-02 963
Spectral TypeF0V
Constellation's Main StarNo
Multiple Star SystemYes
Star Type Main Sequence Dwarf Star
ColourYellow - White
GalaxyMilky Way
ConstellationEridanus
Age0.02 Billion Years Old
Absolute Magnitude 2.85 / 2.88
Visual / Apparent Magnitude5.22
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)04h 37m 36.11
Declination (Dec.)-02° 28` 24.2
Galactic Latitude-30.65767866 degrees
Galactic Longitude198.61235636 degrees
1997 Distance from Earth33.60000 Parallax (milliarcseconds)
 97.07 Light Years
 29.76 Parsecs
2007 Distance from Earth 33.98000 Parallax (milliarcseconds)
 95.99 Light Years
 29.43 Parsecs
 6,070,330.95 Astronomical Units
Galacto-Centric Distance24,214.37 Light Years / 7,424.00 Parsecs
Proper Motion Dec.-64.39000 ± 0.20000 milliarcseconds/year
Proper Motion RA.44.22000 ± 0.34000 milliarcseconds/year
B-V Index0.28
Radial Velocity12.60000 ± 0.30 km/s
Eccentricity0.03470
Semi-Major Axis7504.0000000
Stellar Luminosity (Lsun)5.8500000

Companions (Multi-Star and Exoplanets) Facts


Exoplanet Count1

Estimated Calculated Facts


Radius (x the Sun)1.54
Effective Temperature7,322 Kelvin
Mass Compared to the Sun1.75

Sources and Links


SIMBAD SourceLink

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
29391-02 963.0A5.3000042.00000-59.00000A5White
B11.800003.0000025.000001916

List of Extrasolar Planets orbiting 51 Eridani


NameStatusMass (Jupiters)Orbital Period (Days)EccentricityDiscoveredSemi-Major AxisPeriastronInclination
51 Eri bConfirmed0.31100.0000.4920151284.000135.000

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