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English name:
see Stellar data

III. sign of zodiac



One of the constellations of the zodiac. The sun passes through it from late june to late july. Therefore its best viewed in winter.

Stars and other objects

The two brightest stars alpha Gem, Castor, and beta Gem, Pollux, are worth for observations: Castor has a bightness of 1.6 mag. Viewed with good amateur telescopes this star can be split into three components: Castor A and Castor B revolve each other with a period of 420 years (less good telescopes may only split Castor into two blue-white stars of 2nd and 3rd mag). The third component, Castor C (also known as YY Gem) circulates this pair with a period of several thousand years. Each of the three components is a spectroscopic binary.
Pollux is a red giant of 1.1 mag.
The semiregular variable star eta Gem is a red giant. Its brightness varies from 3rd to 4th magnitude with a period of 230 days. In larger telescopes (apertur at least 150mm) eta Gem reveals a companion of 8.8 mag
Zeta Gem is a 4th mag Cepheid variable that varies 0.4 mag in brightness every 10.2 days.
The two double stars epsilon Gem and 38 Gem are best viewed in small scopes. The first consists of a 3rd mag yellow supergiant with a wide 9th mag companion. The second splits into a pair of withe and yellow 5th and 8th mag stars.
With the help of small telescopes the planetary nebula NGC 2392 reveals an 8th mag blue-green disk about the size of Jupiter. When viewed with larger telescopes it shows a funny shape why it is named Eskimo or Clown Face Nebula.
The open cluster M35 (NGC 2168) is an outstanding cluster with about 200 stars. In binoculars or small telescopes it is visible as a hazy patch. More detailed information about M35 can be found in the Messier database.
One of the most prominent meteor showers radiates from this constellation (from the region around Castor), the geminids. They peak on december 13th and 14th.
The meteor shower rho geminids are visible from end of december to the end of january. They have their peak on 8th of january (there is a second maximum on the 21st of january).

Mythological Background:

The names of the two brightest stars of this constellation, Castor and Pollux, can be found in the greek mythology:
One day Zeus seduced Leda, the wife of the King of Sparta, Tyndareos. To get Leda Zeus changed himself to a swan. Leda became pregant and gave birth to the twins Pollux and Castor and to a girl named Helena. This was the same Helena who was robbed by Paris and brought to Troja; this was the reason for the start of the trojanian war.

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C. Kronberg --- 97/04/21 --- smil at clell.de