Gemini constellation
Gemini (the Twins) is a constellation in the northern sky, best seen in the evening in February. Its brightest star is Pollux (magnitude 1.14). Gemini covers 514 square degrees and is the 30th-largest of the 88 constellations.
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How to find Gemini, step by step
From Rigel through Betelgeuse to the Twins.
- Find Orion on a winter evening.
- Draw a line from Rigel, at Orion's foot, diagonally through Betelgeuse and continue about one and a half times as far.
- You reach Castor and Pollux, the heads of the twins: two bright stars side by side. Pollux is the brighter, slightly orange one; Castor is white. Two long lines of stars run from them back toward Orion.
Detailed star map of Gemini
Facts
| Latin name | Gemini (genitive: Geminorum) |
|---|---|
| Abbreviation | Gem |
| Meaning | the Twins |
| Area | 514 square degrees (30th of 88) |
| Location | right ascension 7.1 h, declination +23° |
| Visible from | latitudes 90° N to 55° S (whole constellation) |
| Best month | February (at about 9 pm) |
| Brightest star | Pollux |
| Stars brighter than magnitude 6 | 75 |
| Named stars (IAU) | 10 |
| Messier objects | M35 |
| Neighbors | Auriga, Canis Minor, Cancer, Lynx, Monoceros, Orion, Taurus |
How to find Gemini
From 40° N (the USA, southern Europe, Japan) look south in February evenings: at about 9 pm Gemini stands highest, around 73° above the southern horizon. From 35° S (Australia, South Africa, Argentina) it is highest in the north, about 32° above the horizon. The months before and after (January and March) are also good: then it is up a couple of hours earlier or later.
Gemini borders Auriga, Canis Minor, Cancer, Lynx, Monoceros, Orion and Taurus.
Asterisms with stars in Gemini: Winter Hexagon.
Stars of Gemini
Gemini has 75 stars brighter than magnitude 6, the limit of the naked eye under a dark sky. These are the brightest:
| Star | Designation | Magnitude | Type | Distance |
|---|---|---|---|---|
| Pollux | β Geminorum | 1.14 | K0IIIb | 34 ly |
| Alhena | γ Geminorum | 1.93 | A0IV | 109 ly |
| Castor | α Geminorum | 1.98 | A1V | 51 ly |
| Tejat | μ Geminorum | 2.88 | M3IIIab | — |
| — | α Geminorum | 2.88 | A2Vm | — |
| Mebsuta | ε Geminorum | 2.98 | G8Ib | — |
| Propus | η Geminorum | 3.28 | M3III | 384 ly |
| Alzirr | ξ Geminorum | 3.36 | F5III | 60 ly |
| Wasat | δ Geminorum | 3.53 | F2IV | 56 ly |
| — | κ Geminorum | 3.57 | G8IIIa | — |
| — | λ Geminorum | 3.58 | A3V | — |
| — | θ Geminorum | 3.6 | A3III | — |
Deep-sky objects in Gemini
Gemini contains one object from Charles Messier's catalog:
- Messier 35 (M35): open cluster, 5.1 mag
Printable Gemini map and outline
A black and white version for printing and a plain outline of the Gemini figure, useful for school projects, worksheets and learning to recognize the shape.
History
Gemini is one of the 48 constellations listed by Ptolemy in the Almagest (2nd century AD). Its official boundary was drawn by Eugène Delporte for the International Astronomical Union in 1930.
Questions about Gemini
What is the brightest star in Gemini?
Pollux, at magnitude 1.14, about 34 light-years away.
When can you see Gemini?
Gemini is best seen in the evening in February. The whole constellation is visible from latitudes between 90° N and 55° S.
How many stars are in Gemini?
75 stars in Gemini are brighter than magnitude 6 and can be seen with the naked eye under a dark sky; 10 of them have official IAU names.
What does Gemini mean?
Gemini means “the Twins” in Latin. Its abbreviation is Gem and the genitive, used in star names such as β Geminorum, is Geminorum.
