Gemini Constellation: Facts About the Twins

Gemini is Latin for "twins," and it is one of the few constellations that actually looks like its namesake. Gemini is one of the Zodiac constellations and one of the 48 constellations described by the 2nd century astronomer Ptolemy.

Locating Gemini

Gemini is fairly easy to spot in the sky, even for amateur star gazers. It is located northeast of Orion, and between Taurus and Cancer on the elliptic.

  • Right ascension: 7 hours
  • Declination: 20 degrees
  • Visible between latitudes 90 and minus 60 degrees
  • Best viewing is during February. By April and May, the constellation can be seen soon after sunset in the west.

Gemini is a constellation high in the winter sky, containing a number of interesting observing targets.
(Image: © Starry Night Software)

The constellation is named after the twins Castor and Pollux in Greek mythology. The two brightest stars — also named after Castor and Pollux — represent the heads of the twins, while fainter stars outline the two bodies. Pollux and orange-giant star (35 light-years) is the brighter of the twins. Castor is a sextuplet star system (50 light-years). Another noteworthy star is Mekbuda (ζ Gem), a super-giant star with a radius that is about 220,000 times the size of the Sun.

The Eskimo Nebula, also known as the Clown Nebula, displays gas clouds so complex they are not fully understood.
(Image: © NASA/Andrew Fruchter (STScI))

Other notable objects in the constellation include the Eskimo Nebula, Medusa Nebula and Geminga, a neutron star. It also include Messier object M35, part of a set of astronomical objects first in 1771 by French astronomer Charles Messier in 1771. M35 stands near the "feet" of the twins and astronomers estimate that the cluster is well more than 100 million years old.


Although the twins Castor and Pollux shared the same mother, Leda, the Queen of Sparta, they had different fathers. Castor's father was Leda’s husband, Tyndarus, the King of Sparta. Pollux's father was the god Zeus, making Pollux immortal while his twin brother Castor was mortal.

The twins, whose sister was Helen of Troy, fought together in the Trojan War. When the mortal Castor eventually died, Pollux was distraught. Pollux’s father, Zeus, decided to make Castor immortal as well and the two of them are together forever as the constellation Gemini.

Astrology is not a science, but Gemini is one of the 13 constellations of the Zodiac. It is the third sign of the Zodiac and represents those born between May 20 and June 20 and is an air sign.

— Kim Ann Zimmermann


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