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Cancer, The Crab Constellation Facts and Mythology

Cancer Constellation Star Map

Cancer (Pronounciation:Can-sir, Abbrev:Cnc, Latin:Cancri) is a constellation, one of 88 constellations that the night sky is divided into. The sky is not divided up equally between the constellations. Cancer takes up 505.872 sq. degrees of the night sky which equates to 1.23% of the night sky. Cancer is the 31st largest in terms of size in the night sky.

The constellation name means The Crab . The constellation is one of the original constellations that was devised by the Ancient Greco-Egyptian astronomer Ptolemy who lived between 90 A.D. and 168 A.D.

There are 6 stars that make up the main constellation. The hipparcos satellite scanned and detailed 1186 stars. There are 48 stars that can be seen with the naked eye in the constellation on a very clear night sky.

Cancer is a member constellation of the Zodiac grouping, a group of 12 star signs that astrologers use to predict someones future based on their date of birth and which constellation appeared when the Sun set. The Zodiac year may be divided up equally between the twelve signs but when they appear in the night sky no longer conforms to the Zodiac calendar. Cancer is an equatorial constellation that can be seen by countries nearest the Equator.

The distance to Cancer is not calculable because all the stars that make up the constellation are at various distances. The best answer for distance to Cancer is to calculate the average distance of the stars.

There are 30 Extrasolar Planets (Exoplanets) in this constellation that are detailed on this site. There is a dedicated page for exoplanets in Cancer.

There are 2 deep space objects that were identified by Charles Messier in this constellation. There are no non-Messier deep space objects in this constellation that are covered at present on this site.

The image at the top right of this page was generated using Night Vision, a free to use and download application by Brian Simspon.

Cancer Star Facts

The caveat of these stars are that they are catalogued on this site. If you know of a star that is nearer or further then do let me know in the comments and I'll add it to the site. The stars mentioned are from the Hipparcos catalogue or have been added because of their special status.

HIP 44539, Cancer's Furthest Star

The furthest star that is located in the constellation is HIP 44539 and it is 163081.7 light years away from the Sun. The furthest figure is derived from either the 1997 or 2007 Hipparcos star catalogue parallax figure and it has been known to produce distances that are wrong.

Altarf, Brightest Star in Cancer

The brightest star in Cancer is Altarf and is located about 35.06 light years from the Sun. The star has a apparent magnitude of 3.53 but an absolute magnitude of -1.31 when the star is viewed from a distance of 10 Parsecs or 32.6 Light Years. The star is only recognised as being Beta Cancri rather than having Alpha status.

5 Cancri, Cancer's Dimmest Visible Star

The dimmest star that can be seen in Cancer with the naked eye is 5 Cancri. The dim star has an apparent magnitude of 5.99. The dimmest star that a person is able to see with their naked eye is 6.0 magnitude based on the table in the reference. Ref: University of Michigan.


Up until the mid-2010, the star was known as 55 Cancri but because of its significance, I.A.U. elected to rename it in a competition. It significance is that Copernicus has a large than usual number of exoplanets in orbit round it. It has five planets in orbit round the star so far known as at April 2018.

Cancer Constellation Mythology

Cancer was a crab in Ancient Greek mythology that Hera sent to make things harder for Hercules . It had little effect on the warrior as Hercules fought Hydra for the second labour. Hercules was the Illegitimate son of Zeus and a mortal. Hera, wife of Zeus was determined to exact revenge for her husband being unfaithful.

Cancer, the Disease

The only connection between Cancer the constellation and Cancer the disease is that they share the same name. You're not at a higher risk of getting the disease if you are born under the constellation of Cancer. Getting Cancer is down to other factors including but not limited to genes, lifestyle including smoking, eating and drinking.

If you are worried, talk to a doctor as I'm no medical professional. The reason why the disease is so called is because in the Ancient Greece, it was noted by Hippocrates and Galen amongst others that the veins round a tumour look like crabs. StackExchange

Meteor Showers Radiating from Cancer

There are 17 Meteor Showers that occur during the year within this constellation based on information gathered from Adam Mickiewicz University (Poland). The list below are major ones and which I have a date period for.

NameActivityPeak ActivityClosest Star
Tau CancridsOct 9-25Oct 17Tau Cancri
Northern delta Cancrids16th January  
Southern delta Cancrids16th January  
Beta Cancrids5th February  

List of Main Stars in Cancer

The following list contains the stars that make up the constellation. For a larger list of stars in the entire constellation area, please visit the For a list of named stars, that is stars that don't start HD or HIP, please visit Cancer Star List page.

NameBayerDistance (Lt.Yr.)Right AscensionDeclinationSpectral TypeColour
AcubensAlpha Cancri188.3208h 58m 29.20+11d 51` 28.0A5mWhite
AltarfBeta Cancri303.4108h 16m 30.95+09d 11` 08.4K4IIIOrange
Asellus BorealisGamma Cancri181.2008h 43m 17.21+21d 28` 06.9A1IVWhite
Asellus AustralisDelta Cancri130.5708h 44m 41.11+18d 09` 17.5K0IIIOrange
Iota Cancri BIota Cancri B279.0108h 46m 40.00+28d 45` 54.6G8II...Yellow
DecapodaIota Cancri A331.1308h 46m 41.83+28d 45` 36.0G8Iab:Yellow

Cancer Facts

Is a Zodiac Sign Yes
Brightest StarAltarf
Area505.872 sq. deg.
Percentage of Night Sky1.23%
Size Position31st
Hemisphere Equatorial
Site Exoplanet Count30
Meteor Shower Count17
Nearest StarCU Cancri
Nearest Star with Exoplanet(s)Copernicus
Brightest StarAltarf
Dimmest Star5 Cancri
Furthest StarHIP 44539
Bright Star Count48
Hipparcos Star Count1186
Main Star Count6
Messier Deep Space Object Count2
*Non-Messier Deep Space Object Count0
Bordering / Neighbouring / Surrounding ConstellationsLynx
Canis Minor
Leo Minor

*Note: The number of Non-Messier Deep Space Object Count relates to how many are covered on this site not how many there are.

List of Deep Space Objects (Galaxies, Nebulas, Supernovas, etc) in Cancer

NameTypeDistanceDeclinationRight Ascension
Messier 67 - King Cobra ClusterOpen Cluster2.61-2.93 kly+11:4908h 50m 4
NGC 2623Galaxy250 MLy+25d 45' 16.7008h 38m 24m 093
Praesepe, the Beehive Cluster (M44, NGC2632)Open Cluster5770+19:5908h 40m 1

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