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81 Ceti - HD16400 - HIP12247

81 Ceti is a white to yellow giant star that can be located in the constellation of Cetus. HIP12247 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD16400. The Id of the star in the Gould Star Catalogue is 277. 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. 81 Ceti has alternative name(s), 81 Ceti , 81 Cet. 81 Ceti has at least 1 Extrasolar Planets believed to be in orbit around the star.

Location of 81 Ceti

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 81 Ceti, the location is 02h 37m 41.78 and -03d23`45.8 .

Proper Motion of 81 Ceti

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 -042.91 ± 000.37 towards the north and 040.18 ± 000.45 east if we saw them in the horizon.

81 Ceti 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 127.0000000 that I have given is based on the Spectral Types page that I have found on the Internet. You might find a different figure, one that may have been calculated rather than generalised that I have done. The figure is always the amount times the luminosity of the Sun. It is an imprecise figure because of a number of factors including but not limited to whether the star is a variable star and distance.

Physical Properties (Colour, Temperature, Mass, Radius) of 81 Ceti

81 Ceti has a spectral type of G5III:. This means the star is a white to yellow giant star. The star has a B-V Colour Index of 1.02 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 4,811 Kelvin.

81 Ceti has been calculated as 9.69 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 6,743,884.85.km. The star's solar mass is 2.00 times that of the Sun's. 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.

The star's metallicity is -0.060000, 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.

81 Ceti Apparent and Absolute Magnitudes

81 Ceti has an apparent magnitude of 5.65 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 0.71 If you used the 2007 Parallax value, you would get an absolute magnitude of 0.82. 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 81 Ceti

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 10.29 which gave the calculated distance to 81 Ceti as 316.97 light years away from Earth or 97.18 parsecs. It would take a spaceship travelling at the speed of light, 316.97 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 10.81 which put 81 Ceti at a distance of 301.72 light years or 92.51 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.

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.

81 Ceti Facts

Alternative Names

Traditional Name81 Ceti
Short Name81 Cet
Alternative Name(s)81 Ceti
Hipparcos Library I.D.12247
Bonner DurchmusterungBD-04 436
Gould I.D.277
Henry Draper Designation16400

Visual Facts

Star Typegiant star
Absolute Magnitude0.71 / 0.82
Apparent Magnitude5.65
Right Ascension (R.A.)02h 37m 41.78
Declination (Dec.)-03d23`45.8
1997 Distance from Earth10.29 Parallax (milliarcseconds)
 316.97 Light Years
 97.18 Parsecs
2007 Revised Distance from Earth10.81 Parallax (milliarcseconds)
 301.72 Light Years
 92.51 Parsecs
Proper Motion Dec.-42.91 ± 0.37 milliarcseconds/year
Proper Motion RA.40.18 ± 0.45 milliarcseconds/year
B-V Index1.02
Spectral TypeG5III:
Colour(G) White to Yellow

Companions (Multi-Star and Exoplanets) Facts

Exoplanet Count1

Estimated Facts

Radius (x the Sun)9.69
Luminosity (x the Sun)127.0000000
Calculated Effective Temperature4,811 Kelvin
Mass Compared to the Sun2.00
Metallicity-0.06000

Sources and Links

SIMBAD SourceLink

Related Stars


List of Extrasolar Planets orbiting 81 Ceti


NameStatusMass (Jupiters)Orbital Period (Days)EccentricityDiscoveredSemi-Major AxisPeriastron
81 Cet BConfirmed5.3952.7000.20620082.5175.000

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