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CI Eridani

CI Eridani Facts

  • CI Eridani is a eclipsing main sequence star that can be located in the constellation of Eridanus. The description is based on the spectral class.
  • CI Eridani is not part of the constellation outline but is within the borders of the constellation.
  • Based on the spectral type (F8V) of the star, the star's colour is yellow to white .
  • The star can not be seen by the naked eye, you need a telescope to see it.
  • Using the most recent figures given by the 2007 Hipparcos data, the star is 381.92 light years away from us. Distance

CI Eridani's Alternative Names

HIP9230 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD12241.

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

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

Location of CI 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 CI Eridani, the location is 01h 58m 38.48 and -53° 31` 39.0 .

Proper Motion of CI 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 -34.77 ± 1.56 milliarcseconds/year towards the north and -22.73 ± 1.82 milliarcseconds/year east if we saw them in the horizon. . 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 CI Eridani

CI Eridani Temperature and Colour

Based on the star's spectral type of F8V , CI Eridani's colour and type is yellow to white main sequence star. The star has a B-V Colour Index of 0.52 which means the star's temperature is about 6,202 Kelvin. The temperature was calculated using information from Morgans @ Uni.edu.

CI Eridani Radius

CI Eridani estimated radius has been calculated as being 0.99 times bigger than the Sun. The Sun's radius is 695,800km, therefore the star's radius is an estimated 692,276.58.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 1.1061078391981478261256024511. 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.

CI Eridani Apparent and Absolute Magnitudes

CI Eridani has an apparent magnitude of 9.66 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 4.55 If you used the 2007 Parallax value, you would get an absolute magnitude of 4.32. 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 CI Eridani

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 9.49000 which gave the calculated distance to CI Eridani as 343.69 light years away from Earth or 105.37 parsecs. If you want that in miles, it is about 2,020,424,754,509,474.92, based on 1 Ly = 5,878,625,373,183.61 miles.

In 2007, Hipparcos data was revised with a new parallax of 8.54000 which put CI Eridani at a distance of 381.92 light years or 117.10 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 24,153,440.51 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.

Travel Time to CI 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)
Walking464,030,475,736.92
Car1202,134,349,191.23
Airbus A380736347,991,715.96
Speed of Sound (Mach 1)767.269333,809,788.94
Concorde (Mach 2)1,534.54166,904,676.94
New Horizons Probe33,0007,761,269.79
Speed of Light670,616,629.00381.92

Variable Type of CI Eridani

The star is a eclipsing Beta Persei (Algol)/ 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. CI Eridani brightness ranges from a magnitude of 10.900 to a magnitude of 9.750 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 CI Eridani Facts and Figures

Visual Facts


Primary / Proper / Traditional NameCI Eridani
Alternative NamesCI Eri, HD 12241, HIP 9230, CI Eri
Spectral TypeF8V
Constellation's Main StarNo
Multiple Star SystemYes
Star Type Main Sequence Dwarf Star
ColourYellow - White
GalaxyMilky Way
ConstellationEridanus
Absolute Magnitude 4.55 / 4.32
Visual / Apparent Magnitude9.66
Naked Eye VisibleRequires a 7x50 Binoculars - Magnitudes
Right Ascension (R.A.)01h 58m 38.48
Declination (Dec.)-53° 31` 39.0
Galactic Latitude-60.82507942 degrees
Galactic Longitude282.29363639 degrees
1997 Distance from Earth9.49000 Parallax (milliarcseconds)
 343.69 Light Years
 105.37 Parsecs
2007 Distance from Earth8.54000 Parallax (milliarcseconds)
 381.92 Light Years
 117.10 Parsecs
 24,153,440.51 Astronomical Units
Proper Motion Dec.-34.77000 ± 1.56000 milliarcseconds/year
Proper Motion RA.-22.73000 ± 1.82000 milliarcseconds/year
B-V Index0.52

Companions (Multi-Star and Exoplanets) Facts


Exoplanet CountNone/Unaware

Variable Star Details


Variable Star ClassEclipsing
Variable Star TypeBeta Persei (Algol)/
Mean Variability Period in Days1.238
Variable Magnitude Range (Brighter - Dimmer)9.750 - 10.900

Estimated Calculated Facts


Radius (x the Sun)1.11
Effective Temperature6,202 Kelvin

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
12241-54 401.4A9.90000G0Yellow
B11.200001914

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