Gemini (constellation)

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Gemini constellation
Gemini constellation map.png
Latin name Gemini
Latin genitive Geminorum
Abbreviation According to
Right ascension 6003006 h 00 m 30 s to  08 h 07 m 58 s80758
declination 2094835+ 9 ° 48 ′ 35 ″ to  + 35 ° 23 ′ 26 ″2352326
surface 513,761 deg²
rank 30
Completely visible 90 ° N to 54.9 ° S
Observation time for Central Europe winter
Number of stars brighter than 3 mag 4th
Brightest star (size) Pollux (1.16)
Meteor streams
Neighboring constellations
clockwise from north )
swell IAU ,

The twins ( Latin Gemini , astronomical sign: ♊) are a constellation of the ecliptic .


The constellation Gemini as seen with the naked eye

The twins form a long rectangle. The strikingly bright stars Castor (Kastor) and Pollux form the two north-eastern corner points.

The band of the Milky Way runs through the western part of Gemini , so several open star clusters can be found in this area .

From around the end of August you can find the twins in the northeast morning sky. In the winter of the northern hemisphere it is high in the south, so that it can be seen completely in the evening sky for the last time in May.

Because the Gemini lie on the ecliptic , the sun , moon and planets move through the constellation. The sun currently passes through Gemini from June 21 through July 21. If you take today's constellation borders as a basis, the summer point was 15 BC. Until October 19, 1989 AD in this constellation.


The twins belong to the 48 constellations of ancient astronomy , which were already described by Claudius Ptolemy . The constellation is the origin of the zodiac sign Gemini . Due to the precession movement of the earth's axis , the passage of the sun has shifted compared to antiquity .

In 1930, the dwarf planet Pluto was discovered while evaluating photographic plates in the Gemini.


For details see article: Dioskuren

In Greek mythology , Castor and Polydeukes (lat. Pollux) were inseparable twin brothers. Her mother, Leda , received Castor from her husband, King Tyndareus of Sparta , and Polydeukes from Zeus , who approached her in the shape of a swan. Hence Castor was human and mortal, while Polydeukes was of divine origin and immortal. The brothers joined Jason and the Argonauts in their search for the golden fleece and experienced numerous adventures. Pollux emerged as the only survivor of a dispute with her companions, the twin brothers Lynkeus and Idas . He turned to his divine Father and asked him to share his own immortality with Castor. From then on the brothers spend their days alternately in Hades or on Mount Olympus . In addition, they were immortalized as a constellation in the sky.

The Arabs saw a lion lying in the constellation.

Celestial objects


B. F. Names or other designations size Lj Spectral class
β 78 Pollux 1.16 m 34 K0 III
α 66 Castor 1.58 m 50 A1 V
γ 24 Alhena , Almeisan 1.93 m 105 A0 IV
μ 13 Tejat Posterior , Nuhatai, Calx 2.94 to 3.00 m 250 M3 III
ε 27 Mebsuta 3.06 m 900 G8 Ib
η 7th Tejat Prior 3.24 to 3.96 m 250 M3 III
ξ 31 Alzir 3.4 m 64 F5 III
δ 55 Wasat 3.50 m 60 F2 IV
θ 34 3.6 m 150 A3 III
κ 77 3.57 m 150 G8 III
λ 54 3.58 m 80 A3 V
ζ 43 Mekbuda 3.7 to 4.2 m 1200 G0 + G1
ι 60 3.78 m 150 K0 III
υ 69 4.06 m 250 M0 III
ν 18th 4.13 m 300 B7 IV
1 4.16 m
ρ 62 4.16 m 60 F0 V
σ 75 4.23 m
τ 46 4.41 m
30th 4.49 m
e 38 4.73 m 80 A9 + G5
ο 71 4.89 m 60 F0 V
A. 57 4.89 m
G 81 4.89 m
χ 4.94 m
φ 83 4.97 m
b 65 5.01 m
f 74 5.04 m
51 5.07 m
64 5.07 m
56 5.09 m
π 80 5.14 m
ω 42 5.20 m
63 5.20 m
d 36 5.28 m

Pollux (β Geminorum), the brightest star in Gemini, is 34 light years away. It is a glowing orange giant star belonging to the spectral class K0.

γ Geminorum is a white shining star of the spectral class A0, 105 light years away. The names Alhena or Almeisan are of old Arabic origin and mean something like "the brand" or "the shining one".

Despite its distance of about 900 light-years, Geminorum is strikingly bright. It is a giant star of the spectral class G5 with 150 times the diameter of our sun.

The Arabic name Mebsuta is derived from "the outstretched paw of the lion".

The star is almost exactly on the ecliptic, so it is sometimes of planets covered . In 1976 the retired Mars from Earth seen just before the star over.

The star δ Geminorum, 60 light-years away, is also in close proximity to the ecliptic. In 1857 it was covered by Saturn . The Arabic name Wasat means "the middle".

Double stars

system Sizes distance
α 1.9 / 2.9 m 4.3 "
ζ 4.0 / 7.6 m 101 "
38 gem 4.7 / sup> / 7.7 m 7.1 "

Castor (α Geminorum) is a complex multiple system in which three main stars revolve around a common center of gravity. Each of the main stars is in turn orbited by a faint companion, which, however, is not visible in the telescope and can only be detected spectroscopically . The three main stars can already be observed with a smaller telescope.

Variable stars

object size period Type
μ 2.94 to 3.00 m irregularly variable
η 3.24 to 3.96 m 235 days, 3 days semi-regular , variable coverage
ζ 3.7 to 4.2 m 10.15 days Coverage variable

μ Geminorum is a variable star whose brightness changes with no apparent regularity. It is a deep red shining star of the spectral class M0. The name Tejat Posterior means the "back foot".

η Geminorum is a red giant 190 light years away, the brightness of which fluctuates with a period of about 235 days. He is a semi-regularly variable (type SRc). In addition, it is an eclipsing star, as it is orbited by a faint companion that partially covers it about every three days.

ζ Geminorum is a variable star of the Delta Cepheid type, 1200 light-years away . The Arabic name Mekbuda is derived from "the drawn paw of the lion".

Messier and NGC objects

Messier (M) NGC other size Type Surname
35 2168 5.5 m Open star cluster
2129 7 m Open star cluster
2158 9 m Open star cluster
2266 9.5 m Open star cluster
2331 9.5 m Open star cluster
2356 9.7 m Open star cluster
2392 9 m Planetary nebula Eskimo mist
2395 8 m Open star cluster
2420 8.3 m Open star cluster

The Messier object M 35 is an open star cluster about 3,000 light years away. It can already be seen as a misty spot with the naked eye. It can be resolved into single stars with prism binoculars . At higher magnification in the telescope, more and more individual stars (around 200 in total) become visible.

NGC 2129 is an open star cluster in 6,000 light years that contains only a few stars.

Near the star δ Geminorum one finds NGC 2392 , a planetary nebula 2,500 light years away. This is the name given to a star that has shed its outer gas envelope at the end of its development. What remains is a white dwarf star . In the telescope, NGC 2392 appears as a foggy round spot. Structures that are reminiscent of a face framed by a fur hood become recognizable in long-exposure photographs. Hence the object was given the name Eskimonebel .

Other objects

Jonckheere 900 , a planetary nebula discovered by Robert Jonckheere in 1912

See also

Web links

Commons : Gemini  album with pictures, videos and audio files
Wiktionary: Gemini  - Explanations of meanings, word origins, synonyms, translations