Gemini

What is Gemini?

Constellations· Winter evenings (N) · two bright stars side by side · December Geminids. The brother stars Castor and Pollux stand side by side as the twins' heads. Radiant of the Geminids — the strongest meteor shower of the year.

Where Gemini is in your sky right now: https://nowsky.org/solar/sky?sel=con:Gemini — location and time set automatically, no login.

Stars of the figure

The 3 brightest of the 8 stars used in the figure (7 lines). Lower magnitude means brighter.

Deep-sky objects near this constellation

Constellation basics

Figures are representative approximations. Source: compiled from NASA and IAU public data.

Frequently asked

When can I see Gemini?

winter.

What is the brightest star in Gemini?

Pollux, magnitude 1.1.

In one line, what is Gemini?

Constellations — The brother stars Castor and Pollux stand side by side as the twins' heads.

Where is Gemini in the sky right now?

Open the sky view for your location and time and it shows the position in the sky right now.

Castor is six stars

Of the two brothers, Castor is not a single star. A small telescope splits it in two, and those two orbit each other in about 450 years. The spectroscope shows each of them to be a binary in turn, and a faint red star a little way off, Castor C, is itself a pair of red dwarfs circling each other in under a day. Six stars make up the system.

At 51 light-years the system consists of four bright A-type stars and two red dwarfs bound in three pairs that orbit one another. In 1803 William Herschel showed that Castor's two stars were revolving around each other, the first evidence that double stars could be systems truly bound by gravity, and over the following two centuries the count grew to six. One of the twins' heads is among the most complex multiple systems in the sky.

The constellation in depth

Gemini is two parallel strands of stars crowned by Castor and Pollux — Pollux slightly brighter and orange, Castor white, and in telescopes actually a sextuple system.

Mid-December's Geminids top 100 meteors an hour — the year's richest shower, and oddly fathered not by a comet but by asteroid Phaethon.

Pluto was discovered near this constellation in 1930, and NASA's Gemini program took its name. Look upper-left of Orion on winter nights for the standing brothers.

Gemini's feet are historic ground: Pluto was discovered in this constellation in 1930, and Herschel first caught Uranus near its border in 1781. Mid-December's Geminid shower is the year's most reliably rich meteor display.

Related

Figures are representative approximations. Simulated positions use J2000 mean elements.