Gemini Constellation Facts

The Gemini constellation represents twin brothers from Greek mythology.

Gemini is visible in the Northern hemisphere and most of the Southern hemisphere.
In the Northern hemisphere the constellation can be seen from winter to spring.
In the Southern hemisphere Gemini can be seen in the summer months.
The constellation will appear upside down in the Southern hemisphere.
Gemini is Latin for twins, although the constellation is based on characters from Greek mythology.
The two large stars which represent the heads of the twins are named after the Greek mythological characters Pollux and Castor.
Pollux and Castor are also the brightest stars in the constellation.
In Chinese philosophy Pollux and Castor are stellar representations of nature's opposites Yin and Yang.
Pollux and Castor were viewed as protectors of sailors by ancient seafarers.
Gemini is also one of the twelve signs of the zodiac.

Gemini Mythology

An artistic representation of the twin brothers Castor and Pollux.

The constellation of Gemini is associated with the Greek mythological characters Castor and Pollux. They were twin brothers born of the same mother but different fathers. The King of Sparta was the father of Castor but the Greek God Zeus was the father of Pollux. In the story their mother, the Queen of Sparta, was ravished by Zeus whilst he was disguised as a swan. Castor and Pollux were said to be born from an egg along with two sisters, one of whom was Helen of Troy.

The twins formed a close bond as they grew up, becoming known as the Dioscuri, or sons of Zeus. In another land a related set of twin brothers were born, over time they became rivals with the Dioscuri. Both sets of twins ended up on the voyage of Jason and the Argonauts and briefly ended their feud. The truce didn’t last long and the mortal Castor was eventually killed by the opposing twins. Zeus reunited the immortal Pollux with his brother by placing both amongst the stars.

Main Stars in the Gemini Constellation

The number next to each star is its apparent magnitude, its brightness from our point of view on Earth, the lower the number the brighter the star in the night sky.

Pollux
An orange giant star which lies around 34 light years from Earth, it is around nine times larger than the sun with twice its mass, Pollux is the brightest star in the Gemini constellation and is also known as Beta Geminorum.

Castor
Also known as Alpha Geminorum, Castor is actually a six star system with three binary stars orbiting around each other, the primary star has around three times the mass of the sun and twice its radius.

Wasat
Also known as Delta Geminorum, Wasat is actually a three star system around 60 light years from Earth, the system consists of a pair of binary stars which are orbited by a third dimmer star.

Mekbuda
A supergiant star with similar surface temperatures to the sun, Mekbuda is around 65 times larger in diameter than the sun with about eight times its mass, also known as Zeta Geminorum.

Mebsuta
A yellowish-orange supergiant around 800 light years from Earth, Mebsuta is around 150 times larger in diameter than the sun with 20 times its mass, also known as Epsilion Geminorum.

Alzirr
A yellow-white star around 60 light years from Earth, Alzirr has a mass around one a half times that of the sun with a radius almost three times greater.

Alhena
A white star in the process of turning into a giant, Alhena is around 100 light years from Earth with a mass and radius around three times that of the sun.

Tejat Posterior
Tejat Posterior is a red giant with a luminosity more than 2,500 times that of the sun, making it one of the brightest stars in the constellation, it is located around 230 light years from Earth.

Propus
A three star system around 350 light years from Earth, the primary star is a red giant, Propus is also known as Tejat Prior and Eta Geminorum.

Finding Gemini - Northern Hemisphere

The chart shows the position of Gemini over most of the United States in mid-winter at 8 pm. This chart can also be applied to other areas of the Northern hemisphere such as Canada, the UK and Europe. Gemini rises in the north-east and sets in the north-west, in December the constellation will appear in the eastern night sky around 9 pm and continue westward before day breaks around 7 am, from January to March it will first appear from the east as night falls around 7 pm before setting around 4 am, and in April it will appear overhead around 8 pm and dip below the horizon around 2 am.

Finding Gemini - Southern Hemisphere

The chart shows the position of Gemini over most of Australia in mid-summer at 10 pm. This chart can also be applied to other areas of the Southern hemisphere such as New Zealand, South Africa and South America. In the Southern hemisphere Gemini rises in the north-east and sets in the north-west, in December the constellation will appear low on the horizon from the north-east at around 1 am and continue westward until day breaks at 6 am, from January to March it will first appear in the north eastern sky as night falls around 10 pm before disappearing below the horizon around 4 am, and in April it will appear in the north around 8 pm and dip below the horizon around midnight.