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Gemini, The Twins Constellation Facts and Mythology

Gemini Constellation Star Map

Gemini (Pronounciation:Gem-in-eye, Abbrev:Gem, Latin:Geminorum) is a constellation, one of 88 constellations that the night sky is divided into. The sky is not divided up equally between the constellations. Gemini takes up 513.761 sq. degrees of the night sky which equates to 1.25% of the night sky. Gemini is the 30th largest in terms of size in the night sky.

The constellation name means The Twins . The constellation is one of the original constellations that was devised by the Ancient Greco-Egyptian astronomer Ptolemy who lived between 90 A.D. and 168 A.D.

There are 17 stars that make up the main constellation. The hipparcos satellite scanned and detailed 1446 stars. There are 74 stars that can be seen with the naked eye in the constellation on a very clear night sky.

Gemini is a member constellation of the Zodiac grouping, a group of 12 star signs that astrologers use to predict someones future based on their date of birth and which constellation appeared when the Sun set. The Zodiac year may be divided up equally between the twelve signs but when they appear in the night sky no longer conforms to the Zodiac calendar. Gemini is an equatorial constellation that can be seen by countries nearest the Equator.

The distance to Gemini is not calculable because all the stars that make up the constellation are at various distances. The best answer for distance to Gemini is to calculate the average distance of the stars.

There are 14 Extrasolar Planets (Exoplanets) in this constellation that are detailed on this site. There is a dedicated page for exoplanets in Gemini. The current largest star so far identified in the constellation of Gemini is TV Geminorum.

There are 1 deep space objects that were identified by Charles Messier in this constellation. There are 1 non-Messier deep space objects that are covered on this site and the list is below.

The image at the top right of this page was generated using Night Vision, a free to use and download application by Brian Simspon.

Gemini Star Facts

The caveat of these stars are that they are catalogued on this site. If you know of a star that is nearer or further then do let me know in the comments and I'll add it to the site. The stars mentioned are from the Hipparcos catalogue or have been added because of their special status.

Gliese 251, Nearest Star

The nearest star to Earth is Gliese 251 which is roughly about 18.22 Light Years from the Earth. The nearest star to the Earth with an exoplanet is HD 50554 which is about 97.57 Light Years.

HD 52961, Furthest Star

The furthest star that is located in the constellation is HD 52961 and it is 163081.7 light years away from the Sun. The furthest figure is derived from either the 1997 or 2007 Hipparcos star catalogue parallax figure and it has been known to produce distances that are wrong.

44 Geminorum, Dimmest Visible Star

The dimmest star that can be seen in Gemini with the naked eye is 44 Geminorum. The dim star has an apparent magnitude of 6. The dimmest star that a person is able to see with their naked eye is 6.0 magnitude based on the table in the reference. Ref: University of Michigan.


Castor is the Alpha star in the constellation but it is not the brightest in the constellation. Castor is a multi-star system of at least three stars which with all the stars together was able to appear brighter than its twin brother Pollux. Castor represents one of the heads of the twins that this constellation is said to represent.


Although it is the brightest star in the constellation, it is afforded that title, it is instead known as Beta Geminorum instead. Pollux is a single star compared to Castor. It is a giant star and one with an exoplanet in orbit round it, something that its brother star doesn't have, a consolation prize.

Gemini Mythology

Zeus seduced Leda, the wife of Tyndareus whilst as a swan. Helen and Pollux were born from eggs. At the same time, Castor and Clytaemnestra were born, children of Tyndareus. Pollux was the son of a god and an immortal, he could not die. They grew up as brothers, competing against one another in competitions and Olympics. During competition between them and their cousins, Idas and Lynceus, Castor died. Pollux asked Zeus to allow him to die so that he could be with his brother which Zeus allowed.

Geminids Meteor Shower

The Geminids are one of the more spectacular meteor showers of the year. They occur at the end of the year, peaking about the 13/14th December. What makes them interesting is that they are multi-coloured rather than all just one colour.

The radiant point for the meteorites is near Castor, the Alpha star in the constellation but not the brightest. The star signifies the right head of the twins. Castor is a multiple star system that when you view closely, you will see it is not just one but a couple of stars.

Whilst meteor showers are associated with comets, this one is associated with an asteroid which was once believed to be a comet but lost all its dust and ice. The asteroid Phaethon orbits closest to the Sun than any other asteroid and has an orbit of roughly 524 days.

Other Meteor Showers

There are 11 Meteor Showers that occur during the year within this constellation based on information gathered from Adam Mickiewicz University (Poland). The list below are major ones and which I have a date period for.

NameActivityPeak ActivityClosest Star
Rho Geminids28-Dec - 28 Jan8/9 JanRho Geminorum
Epsilon GeminidsOct 14 - Oct 27 Oct 18Mebsuta

List of Main Stars in Gemini

The following list contains the stars that make up the constellation. For a larger list of stars in the entire constellation area, please visit the For a list of named stars, that is stars that don't start HD or HIP, please visit Gemini Star List page.

NameBayerDistance (Lt.Yr.)Right AscensionDeclinationSpectral TypeColour
CastorAlpha Geminorum50.8707h 34m 36.00+31d 53` 19.1A2VmWhite
PolluxBeta Geminorum33.7907h 45m 19.36+28d 01` 34.7K0IIIvarOrange
AlhenaGamma Geminorum109.3006h 37m 42.70+16d 23` 57.9A0IVWhite
WasatDelta Geminorum60.4707h 20m 07.39+21d 58` 56.4F0IV...Yellow/White
MebsutaEpsilon Geminorum844.9806h 43m 55.93+25d 07` 52.2A3mA6-A9White
MekbudaZeta Geminorum1376.2207h 04m 06.54+20d 34` 13.1G3Ibv SBYellow
PropusEta Geminorum384.6306h 14m 52.70+22d 30` 24.6M3IIIRed
Theta GeminorumTheta Geminorum189.0806h 52m 47.34+33d 57` 40.9A3IIIWhite
Iota GeminorumIota Geminorum120.3607h 25m 43.68+27d 47` 53.8G9III+...Yellow
Al KirkabKappa Geminorum141.3807h 44m 26.87+24d 23` 53.3G8IIIYellow
Lambda GeminorumLambda Geminorum100.8907h 18m 05.61+16d 32` 25.7A3V...White
TejatMu Geminorum231.6506h 22m 57.59+22d 30` 49.9M3IIIvarRed
Nu GeminorumNu Geminorum544.5106h 28m 57.79+20d 12` 43.8B6IIIBlue/White
AlzirrXi Geminorum58.7006h 45m 17.43+12d 53` 45.8F5IVYellow/White
Tau GeminorumTau Geminorum321.0307h 11m 08.39+30d 14` 43.0K2IIIOrange
Upsilon GeminorumUpsilon Geminorum270.9007h 35m 55.37+26d 53` 45.6K5IIIOrange
35 Geminorum1763.0506h 50m 25.50+13d 24` 47.5K3IIIOrange

Gemini Facts

Is a Zodiac Sign Yes
Largest StarTV Geminorum
Brightest StarPollux
Area513.761 sq. deg.
Percentage of Night Sky1.25%
Size Position30th
Hemisphere Equatorial
Site Exoplanet Count14
Meteor Shower Count11
Nearest StarGliese 251
Nearest Star with Exoplanet(s)HD 50554
Largest StarTV Geminorum
Brightest StarPollux
Dimmest Star44 Geminorum
Furthest StarHD 52961
Bright Star Count74
Hipparcos Star Count1446
Main Star Count17
Messier Deep Space Object Count1
*Non-Messier Deep Space Object Count1
Bordering / Neighbouring / Surrounding ConstellationsAuriga
Canis Minor

*Note: The number of Non-Messier Deep Space Object Count relates to how many are covered on this site not how many there are.

List of Deep Space Objects (Galaxies, Nebulas, Supernovas, etc) in Gemini

NameTypeDistanceDeclinationRight Ascension
Eskimo NebulaPlanetary Nebula2,870 ly+20d 54` 42.48807h 29m 10m 7669
Jellyfish Nebula (IC443)Supernova Remnant500022:31:0506h 17h 13
Messier 35 (NGC2168)Open Cluster2800+24:2006h 08m 9

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