Constellation Cancer (Crab)

Cancer: IAU Constellation Map [150]


The constellation is located between Leo and Gemini on the ecliptic and is rather inconspicuous, because no star is brighter than the 4th magnitude. You can easily recognize it, however, by the somewhat nebulous spot in the sky, which is caused by the open star cluster Praesepe. The constellation extends over an area of 506 square degrees and culminates around midnight on January 30th. [9, 15]

Stars with Proper Names [154]
α Cnc Acubens, Sertan, Sartan
β Cnc Altarf, Al Tarf
γ Cnc Asellus Borealis
δ Cnc Asellus Australis
ζ1 Cnc Tegmen, Tegmine
Data for constellation Cancer [150]
IAU NameCancer
IAU GenitiveCancri
IAU Abbr.Cnc
English NameCrab
Opposition27 January
Season (47° N)November … May
Right Ascension07h 55m 20s … 09h 22m 35s
Declination+06° 28' 12" … +33° 08' 29"
Area506 deg2
Neighbours (N↻)Lyn, Gem, CMi, Hya, Leo, LMi

Deep-Sky Object Descriptions


Constellation Cancer
Constellation Cancer: Illustration from «Uranometria» by Johann Bayer, copper engraving by Alexander Mair, 1603 [28]

Mythology and History

Heracles, son of Zeus and Alcmene, was hated by Hera throughout his life because he was an illegitimate child of her husband Zeus. In a very dangerous situation - when Heracles was fighting the water serpent - and Heracles was already seeming to be victorious, she sent a large, dangerous crab from the Lernaean swamps, which stung painfully in the heel. Hera believed that this would finally destroy Heracles, but the latter stepped on the crab and hurled it away. Hera placed the crab in the sky, in front of the northern water snake, in order to pay homage to it at least in this way. [20, 57]

In the Alfonsin Tables (planet tables created by a college of 50 astronomers on behalf of King Alfons in the years 1248-52 [6]) one finds the transcribed form Carcinus of the Greek name. Ovid also calls the cancer Octipes (eight-footed), although at best one only finds four legs on the star map. But he is also called Litoreus, apparently he was a bank crab (litus = seashore, beach, lake bank, river bank). Cicero calls him Nepa and sees in him an African scorpion. The name Lernaeus mean to say that it comes from the lernian swamps. [6]

The German orientalist Jensen claims that this constellation is identical to the turtle, which was found in the Babylonian and Egyptian cultures as early as 4000 BC. configured. In other Egyptian records from 2000 BC. a scarab, a pill-turner, is seen here. Other names were water beetle, lobster, lobster and cancer minor. According to Julius Schiller's proposal for Christianization, it should become Saint John the Evangelist. [20]


  • [6] «Das neue Lexikon; Band 1-10»; Weltbild Verlag; © Bibliographisches Institut, Mannheim 1984
  • [9] «Drehbare Sternkarte SIRIUS» von H. Suter-Haug; Hallwag-Verlag, Bern
  • [15] «Hartung's Astronomical Objects for Southern Telescopes» by David Malin and David J. Frew; Melbourne University Press 1995; ISBN 0-522-84553-3
  • [20] «Sternbilder und ihre Mythen» von Gerhard Fasching; Zweite, verbesserte Auflage; Springer Verlag Wien, New York; ISBN 3-211-82552-5 (Wien); ISBN 0-387-82552-5 (New York)
  • [28] «Uranometria omnium asterismorum continens schemata, nova methodo delineata aereis laminis expressa» Johann Bayer, Augsburg, 1603; DOI:10.3931/e-rara-309
  • [57] Eye On The Sky: Cancer by Deborah Byrd; Astronomy 2/93, p.52
  • [150] IAU: The Constellations, 11. Oktober 2020;
  • [154] Yale Bright Star Catalog, 15. Oktober 2020;