The constellation Gemini as it can be seen with the unaided eye, with added connecting lines.AFGL 5180 - Through the Clouds.[2]Ananimation of theconstellation Gemini (center), "the twins", shows two parallel stick figures. Gemini is associated with themyth ofCastor and Polydeuces (also known as Pollux), collectively known as the Dioscuri.[3][4]
In classical antiquity, Cancer was the location of the Sun on thenorthern solstice (June 21). During the first century AD,axial precession shifted it into Gemini. In 1990, the location of the Sun at the northern solstice moved from Gemini into Taurus, where it will remain until the 27th century AD and then move intoAries. The Sun will move through Gemini from June 21 to July 20 through 2062.[5]
Gemini is prominent in the winter skies of the northern Hemisphere and is visible the entire night in December–January. The easiest way to locate the constellation is to find its two brightest starsCastor andPollux eastward from the familiar V-shapedasterism (the open clusterHyades) of Taurus and the three stars ofOrion's Belt (Alnitak,Alnilam, andMintaka). Another way is to mentally draw a line from thePleiadesstar cluster located in Taurus and the brightest star inLeo,Regulus. In doing so, an imaginary line that is relatively close to theecliptic is drawn, a line which intersects Gemini roughly at the midpoint of the constellation, just below Castor and Pollux.
When theMoon moves through Gemini, its motion can easily be observed in a single night as it appears first west of Castor and Pollux, then aligns, and finally appears east of them.
The constellation contains 85 stars of naked eye visibility.[6][7]
The brightest star in Gemini is Pollux, and the second-brightest isCastor. Castor'sBayer designation as "Alpha" arose becauseJohann Bayer did not carefully distinguish which of the two was the brighter when he assigned hiseponymous designations in 1603.[8] Although the characters of myth are twins, the actual stars are physically very different from each other.
α Gem (Castor) is a sextuplestar system 52 light-years from Earth, which appears as a magnitude 1.6 blue-white star to the unaided eye. Twospectroscopic binaries are visible at magnitudes 1.9 and 3.0 with a period of 470 years. A wide-setred dwarf star is also a part of the system; this star is anAlgol-typeeclipsing binary star with a period of 19.5 hours; its minimum magnitude is 9.8 and its maximum magnitude is 9.3.
β Gem (Pollux) is an orange-huedgiant star of magnitude 1.14, 34 light-years from Earth. Pollux has anextrasolar planet revolving around it, as do two other stars in Gemini,HD 50554, andHD 59686.
γ Gem (Alhena) is a blue-white hued star of magnitude 1.9, 105 light-years from Earth.
δ Gem (Wasat) is a long-period binary star 59 light-years from Earth. The primary is a white star of magnitude 3.5, and the secondary is anorange dwarf star of magnitude 8.2. The period is over 1000 years; it is divisible in medium amateur telescopes.
ε Gem (Mebsuta), adouble star, includes a primaryyellow supergiant of magnitude 3.1, nine hundred light-years from Earth. The optical companion, of magnitude 9.6, is visible in binoculars and small telescopes.[8]
ζ Gem (Mekbuda) is a double star, whose primary is aCepheid variable star with a period of 10.2 days; its minimum magnitude is 4.2 and its maximum magnitude is 3.6. It is a yellow supergiant, 1,200 light-years from Earth, with a radius that is 60 times solar, making it approximately 220,000 times the size of theSun. The companion, a magnitude 7.6 star, is visible in binoculars and small amateur telescopes.
η Gem (Propus) is a binary star with a variable component. 380 light-years away, it has a period of 500 years and is only divisible in large amateur telescopes. The primary is asemi-regularred giant with a period of 233 days; its minimum magnitude is 3.9 and its maximum magnitude is 3.1. The secondary is of magnitude 6.[8]
κ Gem is a binary star 143 light-years from Earth. The primary is ayellow giant of magnitude 3.6; the secondary is of magnitude 8. The two are only divisible in larger amateur instruments because of the discrepancy in brightness.
ν Gem is a double star divisible in binoculars and small amateur telescopes. The primary is ablue giant of magnitude 4.1, 550 light-years from Earth, and the secondary is of magnitude 8.
38 Gem, a binary star, is also divisible in small amateur telescopes, 84 light-years from Earth. The primary is a white star of magnitude 4.8 and the secondary is a yellow star of magnitude 7.8.[8]
M35 (NGC 2168) is a large, elongatedopen cluster of magnitude 5, discovered in the year 1745 by Swiss astronomerPhilippe Loys de Chéseaux. It has an area of approximately 0.2square degrees, the same size as the full moon. Its high magnitude means that M35 is visible to the unaided eye under dark skies; under brighter skies it is discernible in binoculars. The 200 stars of M35 are arranged in chains that curve throughout the cluster; it is 2800 light-years from Earth. Another open cluster in Gemini isNGC 2158. Visible in large amateur telescopes and very rich, it is more than 12,000 light-years from Earth.[8]
NGC 2392 is aplanetary nebula with an overall magnitude of 9.2, located 4,000 light-years from Earth.[10] In a small amateur telescope, its 10th magnitude central star is visible, along with its blue-green elliptical disk. It is said to resemble the head of a person wearing aparka.[8]
The Medusa Nebula is another planetary nebula, some 1,500 light-years distant.Geminga is aneutron star approximately 550 light-years from Earth. Other objects includeNGC 2129,NGC 2158,NGC 2266, NGC 2331 andNGC 2355.
TheGeminids is a bright meteor shower that peaks on December 13–14. It has a maximum rate of approximately 100 meteors per hour, making it one of the richest meteor showers.[8] TheEpsilon Geminids peak between October 18 and October 29 and have only been recently confirmed. They overlap with theOrionids, which make the Epsilon Geminids difficult to detect visually. Epsilon Geminid meteors have a higher velocity than Orionids.[11]
Gemini as depicted inUrania's Mirror, a set of constellation cards published in London c.1825.Sculpture showingCastor and Pollux, the legend behind the thirdastrological sign in the Zodiac and the constellation of Gemini
InBabylonian astronomy, the stars Castor and Pollux were known as the Great Twins. The Twins were regarded as minor gods and were calledMeshlamtaea and Lugalirra, meaning respectively 'The One who has arisen from the Underworld' and the 'Mighty King'. Both names can be understood as titles of Nergal, the major Babylonian god of plague and pestilence, who was king of the Underworld.[12]
InGreek mythology, Gemini was associated with the myth of Castor and Pollux, the children ofLeda andArgonauts both. Pollux was the son ofZeus, who seduced Leda, while Castor was the son ofTyndareus, king ofSparta and Leda's husband. Castor and Pollux were also mythologically associated withSt. Elmo's fire in their role as the protectors of sailors.[13] When Castor died, because he was mortal, Pollux begged his father Zeus to give Castor immortality, and he did, by uniting them together in the heavens.
Diagram ofH. A. Rey's alternative way to connect the stars of the constellation Gemini. Twins are shown holding hands.
Gemini is dominated by Castor and Pollux, two bright stars that appear relatively very closely together forming an o shape, encouraging the mythological link between the constellation and twinship. The twin above and to the right (as seen from the Northern Hemisphere) is Castor, whose brightest star is α Gem; it is a second-magnitude star and represents Castor's head. The twin below and to the left is Pollux, whose brightest star is β Gem (more commonly called Pollux); it is of the first magnitude and represents Pollux's head. Furthermore, the other stars can be visualized as two parallel lines descending from the two main stars, making it look like two figures.
H. A. Rey has suggested an alternative to the traditional visualization that connected the stars of Gemini to show twins holding hands. Pollux's torso is represented by the starυ Gem, Pollux's right hand byι Gem, Pollux's left hand byκ Gem; all three of these stars are of the fourth magnitude. Pollux's pelvis is represented by the starδ Gem, Pollux's right knee byζ Gem, Pollux's right foot byγ Gem, Pollux's left knee byλ Gem, and Pollux's left foot byξ Gem. γ Gem is of the second magnitude, while δ and ξ Gem are of the third magnitude. Castor's torso is represented by the starτ Gem, Castor's left hand byι Gem (which he shares with Pollux), Castor's right hand byθ Gem; all three of these stars are of the fourth magnitude. Castor's pelvis is represented by the starε Gem, Castor's left foot byν Gem, and Castor's right foot byμ Gem andη Gem; ε, μ, and η Gem are of the third magnitude. The brightest star in this constellation is Pollux.
InMeteorologica (1 343b30)Aristotle mentions that he observed Jupiter inconjunction with and thenocculting a star in Gemini. This is the earliest-known observation of this nature.[14] A study published in 1990 suggests the star involved was 1 Geminorum and the event took place on 5 December 337 BC.[15]
As of 2011[update], the Sun appears in the constellation Gemini from June 21 to July 20. Intropical astrology, the Sun is considered to be in the signGemini from May 22 to June 21, and insidereal astrology, from June 16 to July 16.[18]
^Star Names: Their Lore and Meaning by Richard Hinckley Allen, Dover, 1963, page 229
^Cohen, Sheldon M.; Burke, Paul (1990). "New Evidence for the Dating of AristotleMeteorologica 1-3".Classical Philology.85 (2):126–129.doi:10.1086/367188.JSTOR269702.S2CID162257274.
^Star Names: Their Lore and Meaning by Richard Hinckley Allen, Dover, 1963, page 236
^The Cambridge Guide to the Constellations by Michael E. Bakich, Cambridge University Press, 1995, page 210
^Robert Dinwiddie; David Hughes; Geraint H. Jones; Ian Ridpath; Carole Stott; Giles Sparrow.The Stars: The Definitive Visual Guide to the Cosmos. DK Publishing. p. 166.
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