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20 Geminorum

20 Geminorum Facts

20 Geminorum's Alternative Names

HIP31158 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD46136.

Flamsteed designations are named after the creator, Sir John Flamsteed. Sir John numbered the stars in the constellation with a number and the latin name, this star's Flamsteed designation is 20 Geminorum with it shortened to 20 Gem.

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+17 1286.

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

Location of 20 Geminorum

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 20 Geminorum, the location is 06h 32m 18.52 and +17° 47` 03.4 .

Radial Velocity and Proper Motion of 20 Geminorum

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 22.89 ± 3.52 milliarcseconds/year towards the north and 50.09 ± 4.64 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 1.50 km/s with an error of about 0.40 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 (Colour, Temperature, Age) of 20 Geminorum

20 Geminorum Colour and Temperature

20 Geminorum has a spectral type of F6V.... This means the star is a blue to white main sequence star. The star has a B-V Colour Index of 0.54 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 6,122 Kelvin.

20 Geminorum Radius

Radius has been calculated as being 5.05 times bigger than the Sun. The Sun's radius is 695,800km, therefore the star's radius is an estimated 3,512,291.69.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 3.72. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures. The star's Iron Abundance is 0.10 with an error value of 0.08 Fe/H with the Sun has a value of 1 to put it into context.

The stars age according to Hipparcos data files put the star at an age of about 2.30 Billion years old but could be between 2.00 and 2.60 Billion years old. In comparison, the Sun's age is about 4.6 Billion Years Old.

20 Geminorum Apparent and Absolute Magnitudes

20 Geminorum has an apparent magnitude of 6.26 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 1.08 If you used the 2007 Parallax value, you would get an absolute magnitude of 1.74. 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 Geminorum

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 9.21 which gave the calculated distance to 20 Geminorum as 354.14 light years away from Earth or 108.58 parsecs. It would take a spaceship travelling at the speed of light, 354.14 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 12.46 which put 20 Geminorum at a distance of 261.77 light years or 80.26 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 16,554,697.99 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.

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 20 Geminorum Facts and Figures

Visual Facts


Primary / Proper / Traditional Name20 Geminorum
Alternative NamesHD 46136, HIP 31158, 20 Gem, BD+17 1286
Spectral TypeF6V...
Constellation's Main StarNo
Multiple Star SystemYes
Star Type Main Sequence Dwarf Star
ColourYellow - White
GalaxyMilky Way
ConstellationGemini
Age2.30 Billion Years Old
Age Range2.00 - 2.60 Billion Years Old
Absolute Magnitude 1.08 / 1.74
Visual / Apparent Magnitude6.26
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)06h 32m 18.52
Declination (Dec.)+17° 47` 03.4
Galactic Latitude3.93 degrees
Galactic Longitude194.95 degrees
1997 Distance from Earth9.21 Parallax (milliarcseconds)
 354.14 Light Years
 108.58 Parsecs
2007 Distance from Earth12.46 Parallax (milliarcseconds)
 261.77 Light Years
 80.26 Parsecs
 16,554,697.99 Astronomical Units
Proper Motion Dec.22.89 ± 3.52 milliarcseconds/year
Proper Motion RA.50.09 ± 4.64 milliarcseconds/year
B-V Index0.54
Radial Velocity1.50 ± 0.40 km/s
Iron Abundance0.10 ± 0.08 Fe/H
Associated / Clustered Stars20 Geminorum B

Companions (Multi-Star and Exoplanets) Facts


Exoplanet CountNone/Unaware

Estimated Calculated Facts


Radius (x the Sun)3.72
Effective Temperature6,122 Kelvin

Sources and Links


SIMBAD SourceLink

Related Stars


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