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Sigma Geminorum, 75 Geminorum, HD62044, HIP37629, HR2973

Sigma Geminorum is a orange to red eclipsing binary system giant star that can be located in the constellation of Gemini. The description is based on the spectral class. The star can be seen with the naked eye, that is, you don't need a telescope/binoculars to see it.

Sigma Geminorum's Alternative Names

Sigma Geminorum (Sig Gem) is the Bayer Classification for the star. The Id of the star in the Yale Bright Star Catalogue is HR2973. HIP37629 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD62044.

Sigma Geminorum has alternative name(s) :- , sig Gem.

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 75 Geminorum with it shortened to 75 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+29 1590.

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

Location of Sigma Geminorum

The location of the 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 star is compared to the celestial equator and is expressed in degrees. For Sigma Geminorum, the location is 07h 43m 18.69 and +28° 53` 02.7 .

Proper Motion of Sigma Geminorum

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 -230.32 ± 0.09 miliarcseconds/year towards the north and 62.66 ± 0.19 miliarcseconds/year east if we saw them in the horizon. The Radial Velocity, that is the speed at which the star is moving away/towards us is 44.15000 km/s with an error of about 0.09 km/s .

Sigma Geminorum 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 40.68 that I have given is based on the value in the Simbad Hipparcos Extended Catalogue at the University of Strasbourg from 2012.

Physical Properties (Colour, Temperature) of Sigma Geminorum

Sigma Geminorum has a spectral type of K1III SB. This means the star is a orange to red giant star. The star is 7,435.00 Parsecs from the Galactic Centre or terms of Light Years is 24,250.24 s. The star has a B-V Colour Index of 1.11 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 4,646 Kelvin.

Sigma Geminorum Radius has been calculated as being 7.70 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 5,360,632.90.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 7.88. 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 -0.06 with an error value of 9.99 Fe/H with the Sun has a value of 1 to put it into context.

Sigma Geminorum Apparent and Absolute Magnitudes

Sigma Geminorum has an apparent magnitude of 4.23 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 1.36 If you used the 2007 Parallax value, you would get an absolute magnitude of 1.31. 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 Sigma Geminorum

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 26.68 which gave the calculated distance to Sigma Geminorum as 122.25 light years away from Earth or 37.48 parsecs. It would take a spaceship travelling at the speed of light, 122.25 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 26.08 which put Sigma Geminorum at a distance of 125.06 light years or 38.34 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.

The star's Galacto-Centric Distance is 7,435.00 Parsecs or 24,250.24 Light Years. The Galacto-Centric Distance is the distance from the star to the Centre of the Galaxy which is Sagittarius A*.

Variable Type of Sigma Geminorum

The star is a eclipsing binary system RS 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. Sigma Geminorum brightness ranges from a magnitude of 4.448 to a magnitude of 4.375 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 0.1 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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Sigma Geminorum Facts

Visual Facts


Primary / Proper / Traditional NameSigma Geminorum
Alternative NamesSig Gem, HD 62044, HIP 37629, HR 2973, 75 Geminorum, 75 Gem, BD+29 1590, sig Gem
Spectral TypeK1III SB
Multiple Star SystemYes
Star TypeGiant Star
Colour orange to red
GalaxyMilky Way
ConstellationGemini
Absolute Magnitude1.36 / 1.31
Visual / Apparent Magnitude4.23
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)07h 43m 18.69
Declination (Dec.)+28° 53` 02.7
Galactic Latitude23.27 degrees
Galactic Longitude191.19 degrees
1997 Distance from Earth26.68 Parallax (milliarcseconds)
 122.25 Light Years
 37.48 Parsecs
2007 Distance from Earth26.08 Parallax (milliarcseconds)
 125.06 Light Years
 38.34 Parsecs
Galacto-Centric Distance24,250.24 Light Years / 7,435.00 Parsecs
Proper Motion Dec.-230.32 ± 0.09 milliarcseconds/year
Proper Motion RA.62.66 ± 0.19 milliarcseconds/year
B-V Index1.11
Radial Velocity44.15 ± 0.09 km/s
Iron Abundance-0.06 ± 9.99 Fe/H
Eccentricity0.31
Semi-Major Axis5478.00
Stellar Luminosity (Lsun)40.68

Companions (Multi-Star and Exoplanets) Facts


Exoplanet CountNone/Unaware

Variable Star Details


Variable Star ClassEclipsing binary system
Variable Star TypeRS Canum Venaticorum
Mean Variability Period in Days0.072
Variable Magnitude Range (Brighter - Dimmer)4.375 - 4.448

Estimated Facts


Calculated Effective Temperature4,646 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
62044+29 1590.0A4.3000068.00000-233.00000K0Orange
B10.800001909

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