Gemini Constellation

Gemini is the constellation of the Twins, named for Castor and Pollux, the inseparable brothers of Greek and Roman myth. Two bright stars bearing their names mark the twins' heads, with fainter lines of stars trailing off to represent their bodies, side by side as if walking hand in hand across the winter sky. Gemini has long stood for loyalty, brotherhood, and duality, and its two anchor stars make it one of the easier zodiac constellations to pick out once you know where to look.

Gemini at a Glance

• AbbreviationGem
• Genitive FormGeminorum
• MeaningThe Twins
• Constellation FamilyZodiac
• Area514 sq. degrees (30th largest of 88)
• Right Ascension5h 55m – 8h 05m
• Declination+10° to +35°
• Brightest StarPollux (magnitude 1.14)
• Best Evening ViewingFebruary, visible 90°N to 60°S
• Sun's Actual TransitJune 21 – July 20 (astrology: May 21 – June 20)

Mythology and History

Castor and Pollux were the sons of Leda, though myth gives them different fathers: Pollux was said to be the son of Zeus and therefore immortal, while Castor was mortal, fathered by Leda's husband Tyndareus. When Castor was killed, Pollux begged to share his own immortality with his brother rather than live forever without him, and Zeus obliged by placing them together among the stars, forever reunited. The Dioscuri, as the pair were known, were also honored as protectors of sailors and were invoked as patrons of hospitality. Gemini was one of the 48 constellations recorded by Ptolemy in the 2nd century AD, and its twin bright stars have marked the same spot in the winter sky for that entire span of recorded history.

Notable Stars in Gemini

Confusingly, Pollux, not Castor, is the brighter of the two — an orange giant star at magnitude 1.14, about 34 light-years from Earth, making it the closest giant star to our own solar system. Castor, meanwhile, only looks like a single star to the naked eye; through a telescope, and by spectroscopic analysis, it resolves into six individual stars locked in a complex gravitational dance roughly 51 light-years away, one of the most remarkable multiple-star systems visible from Earth.

Deep-Sky Objects

Gemini sits along the winter Milky Way and rewards binocular sweeps. M35 is a large, bright open cluster of several hundred young stars near Castor's foot, visible to the naked eye as a faint haze under dark skies and resolving into individual stars through binoculars. The Eskimo Nebula (NGC 2392), a planetary nebula formed from the outer layers of a dying sun-like star, is a favorite target for larger amateur telescopes thanks to its intricate, face-like structure.

• M35 — a rich open star cluster of several hundred stars near Castor's foot, visible to the naked eye as a faint patch under dark skies
• Eskimo Nebula (NGC 2392) — a small, detailed planetary nebula, the glowing shell cast off by a dying star, resembling a face ringed by a fur hood in larger telescopes

Neighboring Constellations and How to Find It

Gemini lies between Taurus and Cancer, just northeast of Orion, and is easiest to find by tracing a line from Orion's belt up through Betelgeuse toward the two parallel bright stars, Castor and Pollux. It reaches its highest point in the evening sky around February and is visible across nearly the entire globe. Gemini borders Taurus, Auriga, Lynx, Cancer, Canis Minor, Monoceros, and Orion.

Gemini is also associated with the Geminids and Rho Geminids meteor showers, visible to observers who track where these annual displays radiate from.