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3 Geminorum

3 Geminorum Facts

  • 3 Geminorum is a supergiant star that can be located in the constellation of Gemini. The description is based on the spectral class.
  • 3 Geminorum is not part of the constellation outline but is within the borders of the constellation.
  • Based on the spectral type (B2.5Ib) of the star, the star's colour is blue .
  • The star can be seen with the naked eye, that is, you don't need a telescope/binoculars to see it.
  • Using the most recent figures given by the 2007 Hipparcos data, the star is 14181.01 light years away from us. Distance

3 Geminorum's Alternative Names

The Id of the star in the Yale Bright Star Catalogue is HR2173. HIP29225 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD42087.

3 Geminorum has alternative name(s) :- PU Gem, PU Gem.

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 3 Geminorum. The Flamsteed name can be shortened to 3 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+23 1226.

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

Location of 3 Geminorum

The location of the supergiant 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 3 Geminorum, the location is 06h 09m 43.99 and +23° 06` 48.5 .

Radial Velocity and Proper Motion of 3 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 -2.65 ± 0.45 milliarcseconds/year towards the north and -0.92 ± 0.88 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 16.00000 km/s with an error of about 4.30 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 3 Geminorum

3 Geminorum Temperature and Colour

Based on the star's spectral type of B2.5Ib , 3 Geminorum's colour and type is blue supergiant star. The star has a B-V Colour Index of 0.19 which means the star's temperature is about 7,480 Kelvin. The temperature was calculated using information from Morgans @ Uni.edu.

3 Geminorum Radius

3 Geminorum Apparent and Absolute Magnitudes

3 Geminorum has an apparent magnitude of 5.75 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 If you used the 2007 Parallax value, you would get an absolute magnitude of -7.44. 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 3 Geminorum

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as -0.51000 which gave the calculated distance to 3 Geminorum as -6395.36 light years away from Earth or -1960.78 parsecs. If you want that in miles, it is about -37,595,925,566,643,532.05, based on 1 Ly = 5,878,625,373,183.61 miles.

In 2007, Hipparcos data was revised with a new parallax of 0.23000 which put 3 Geminorum at a distance of 14181.01 light years or 4347.83 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 896,798,063.57 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 3 Geminorum

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)
Walking42,377,505,280,503.82
Car12079,250,176,016.79
Airbus A38073612,921,224,350.56
Speed of Sound (Mach 1)767.26912,394,637,502.64
Concorde (Mach 2)1,534.546,197,310,674.22
New Horizons Probe33,000288,182,458.24
Speed of Light670,616,629.0014,181.01
3 Geminorum brightness ranges from a magnitude of 5.821 to a magnitude of 5.778 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 6.8 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 3 Geminorum Facts and Figures

Visual Facts


Primary / Proper / Traditional Name3 Geminorum
Alternative NamesPU Gem, HD 42087, HIP 29225, HR 2173, 3 Gem, BD+23 1226, PU Gem
Spectral TypeB2.5Ib
Constellation's Main StarNo
Multiple Star SystemYes
Star Type very luminous Supergiant Star less luminour Supergiant Star
ColourBlue
GalaxyMilky Way
ConstellationGemini
Absolute Magnitude / -7.44
Visual / Apparent Magnitude5.75
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)06h 09m 43.99
Declination (Dec.)+23° 06` 48.5
Galactic Latitude1.76877917 degrees
Galactic Longitude187.75178185 degrees
1997 Distance from Earth-0.51000 Parallax (milliarcseconds)
 -6395.36 Light Years
 -1960.78 Parsecs
2007 Distance from Earth0.23000 Parallax (milliarcseconds)
 14181.01 Light Years
 4347.83 Parsecs
 896,798,063.57 Astronomical Units
Proper Motion Dec.-2.65000 ± 0.45000 milliarcseconds/year
Proper Motion RA.-0.92000 ± 0.88000 milliarcseconds/year
B-V Index0.19
Radial Velocity16.00000 ± 4.30 km/s

Companions (Multi-Star and Exoplanets) Facts


Exoplanet CountNone/Unaware

Variable Star Details


Mean Variability Period in Days6.807
Variable Magnitude Range (Brighter - Dimmer)5.778 - 5.821

Estimated Calculated Facts


Effective Temperature7,480 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
42087+23 1226.0A5.80000-2.000009.00000B1Blue/White
B9.900001891
C14.400001891

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