The constellation Gemini


Nom latin
Hémisphère nord
October - April
514 deg²
Étoile la plus brillante
Pollux (HIP number 37826)
Open star clusters, planetary nebula
The constellation Gemini

Gemini represents the twins Castor and Pollux and is one of the 48 constellations that the Greco-Roman astronomer Claudius Ptolemy already described in ancient times. It is a prominent constellation that has several interesting deep-sky objects to observe. Additionally, it is the origin of the astrological zodiac sign Gemini, which today is assigned great significance.

Hemisphere, visibility, and area

The Gemini constellation lies in the northern celestial sky and can be seen from many places. From the northern hemisphere, it can be observed from anywhere, and from the southern hemisphere, it can be seen up to the 55th parallel. This means it can be seen deep in the south of Patagonia, but it cannot be observed from the Antarctic and the surrounding ocean.

The best time to watch Gemini is from October to April when it appears with an area of approximately 514 square degrees. In comparison to all other 88 constellations, Gemini ranks 30th in size.

Gemini is located on the ecliptic, the apparent path of the sun and other planets, meaning that the sun passes through this constellation at the same time each year. This period is from June 21 to July 21. During this time, Gemini is not visible as it rises and sets with the sun.

Astrologically, the sun travels through Gemini from May 22 to June 21. However, this period was determined thousands of years ago and is currently inaccurate due to the precession of the earth. It has shifted by about one month.

The constellation is easily recognizable in the sky as the stars form an elongated rectangle, with the two brightest stars marking the northeast corners. Some visualizations also connect stars to form the arms and legs of the twins.

Castor (Latin: α Geminorum, Alpha Geminorum) is a double-star system roughly 51 light-years from earth. Pollux (Latin: β Geminorum, Beta Geminorum) is the brighter of the two stars and is a red giant approximately 34 light-years away. In mythology, both stars represent twins.

Gemini is surrounded by seven other constellations in the sky. Along the ecliptic, Taurus is to the east, and Cancer is to the west. In the southeast, the well-known constellation Orion is located. Other neighbors include Auriga, Monoceros, Canis Minor, and Lynx.

Specialties in the constellation

In the western region of Gemini lies the Milky Way band, which contains some open star clusters and a planetary nebula.

The brightest open star cluster is NGC 2168, also known as M35 (Messier 35), with an apparent magnitude of roughly 5.1. The second name comes from the French astronomer Charles Messier. M35 is located about 3,000 light-years away and can be seen as a hazy patch on clear nights with the naked eye. In a prism binocular, it can already be resolved into individual stars that appear prominently red.

A telescope is needed to observe the planetary nebula NGC 2392, also known as the Eskimo Nebula. In a binocular, it is only visible as a faint point of light because its apparent magnitude is only about 9.1 mag. The nebula was formed about 10,000 years ago and is located about 3,000 light-years away from our solar system.


According to one version of Greek mythology, Castor and Pollux were two inseparable brothers. They had the same mother but different fathers. Castor's father was King Tyndareus of Sparta, while the Olympic god Zeus fathered Pollux in the form of a swan. Pollux, the son of the god Zeus, was immortal, while Castor's mortal father made him mortal as well.

The two brothers shared many adventures together. They even accompanied the Argonauts and their leader Jason in search of the Golden Fleece. However, during this journey, a serious conflict arose, and only the immortal Pollux survived.

In painful mourning for Castor, his brother Pollux turned to his father Zeus and asked for Castor's immortality. His wish was granted. Zeus placed the twins in the sky, forever united in brotherly love.

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