Cancer constellation
Cancer (the Crab) is a constellation in the northern sky, best seen in the evening in March. Its brightest star is Tarf (magnitude 3.52). Cancer covers 506 square degrees and is the 31st-largest of the 88 constellations.
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How to find Cancer, step by step
The faint crab between Gemini and Leo.
- Cancer has no bright stars; find its neighbors first: Pollux in Gemini and Regulus in Leo.
- About halfway between them, under a dark sky, a fuzzy patch is visible to the naked eye: the Beehive Cluster (M44), the center of Cancer.
- Binoculars show dozens of stars in the Beehive; the faint stars around it form an upside-down Y.
Detailed star map of Cancer
Facts
| Latin name | Cancer (genitive: Cancri) |
|---|---|
| Abbreviation | Cnc |
| Meaning | the Crab |
| Area | 506 square degrees (31st of 88) |
| Location | right ascension 8.7 h, declination +19° |
| Visible from | latitudes 90° N to 57° S (whole constellation) |
| Best month | March (at about 9 pm) |
| Brightest star | Tarf |
| Stars brighter than magnitude 6 | 51 |
| Named stars (IAU) | 9 |
| Messier objects | M44, M67 |
| Neighbors | Canis Minor, Gemini, Hydra, Leo, Lynx |
How to find Cancer
From 40° N (the USA, southern Europe, Japan) look south in March evenings: at about 9 pm Cancer stands highest, around 69° above the southern horizon. From 35° S (Australia, South Africa, Argentina) it is highest in the north, about 36° above the horizon. The months before and after (February and April) are also good: then it is up a couple of hours earlier or later.
Cancer borders Canis Minor, Gemini, Hydra, Leo and Lynx.
Stars of Cancer
Cancer has 51 stars brighter than magnitude 6, the limit of the naked eye under a dark sky. These are the brightest:
| Star | Designation | Magnitude | Type | Distance |
|---|---|---|---|---|
| Tarf | β Cancri | 3.52 | K4IIIBa0.5 | 303 ly |
| Asellus Australis | δ Cancri | 3.94 | K0III-IIIb | 137 ly |
| — | ι Cancri | 4.02 | G7.5IIIaBa0.1 | — |
| Acubens | α Cancri | 4.25 | A5m | 178 ly |
Deep-sky objects in Cancer
Cancer contains 2 objects from Charles Messier's catalog:
- Beehive Cluster (M44): open cluster, 3.1 mag
- Messier 67 (M67): open cluster, 7.6 mag
Printable Cancer map and outline
A black and white version for printing and a plain outline of the Cancer figure, useful for school projects, worksheets and learning to recognize the shape.
History
Cancer 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 Cancer
What is the brightest star in Cancer?
Tarf, at magnitude 3.52, about 303 light-years away.
When can you see Cancer?
Cancer is best seen in the evening in March. The whole constellation is visible from latitudes between 90° N and 57° S.
How many stars are in Cancer?
51 stars in Cancer are brighter than magnitude 6 and can be seen with the naked eye under a dark sky; 9 of them have official IAU names.
What does Cancer mean?
Cancer means “the Crab” in Latin. Its abbreviation is Cnc and the genitive, used in star names such as β Cancri, is Cancri.
