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Cancer Constellation: Facts About the Crab

Cancer, which is Latin for crab, is the dimmest of the 13 constellations of the Zodiac, having only two stars above the fourth magnitude.

Locating Cancer the Crab

Cancer lies between Leo, the lion, and Gemini, the twins. It is almost impossible to see Cancer as a crab with the naked eye or even binoculars. It looks more like a faint, upside-down Y.

Cancer March 2012 Sky Map
The small faint constellation Cancer is rich in open clusters and double stars.
Credit: Starry Night Software

Cancer is visible in the northern hemisphere in the early spring. It can be seen in the southern hemisphere during autumn. The Cancer constellation occupies an area of 506 square degrees.

  • Right ascension: 9 hours
  • Declination: 20 degrees
  • Best seen between latitudes 90 degrees and minus 60degrees
  • Visibility is best during March at 9 p.m.

Cancer contains two Messier objects, a set of astronomical objects first in 1771 by French astronomer Charles Messier in 1771. Cancer’s most famous Messier object is M44, also known as the Beehive Cluster, which is a small star cluster that resembles a swarm of bees. M44 contains about 50 stars, the brightest of which are of the sixth magnitude. ε Cnc is the brightest member at magnitude 6.3. Praesepe is also one of the larger visible open clusters with an area of 1.5 square degrees, or three times the size of the full moon.

The constellation’s other Messier object, M67, is another open star cluster.

β Cnc is the brightest star in Cancer at magnitude 3.5. It is an orange-hued giant star about 290 light-years from Earth.

The star α Cnc (Acubens), which means "the claw" is a double star with a primary of magnitude 4.3, 173 light-years from Earth.

Other notable stars include the γ Cnc (Asellus Borealis), the "northern donkey," a white-hued star (158 light-years), and δ Cnc (Asellus Australis), "southern donkey," an orange-hued giant star (136 light-years).

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Mythology

The constellation of Cancer represents the giant crab that attacked Hercules during the second of his 12 labors he performed as penance for killing his family. It was sent by the jealous goddess Hera thwart Hercules as he battled the water serpent Hydra, but he killed it with his club.

In astrology, which is not a science, Cancer is the fourth sign of the Zodiac and represents those born between June 20 to July 22. It is considered a water sign and is one of the four cardinal signs, which are signs that indicate a change of season when the sun makes its annual passage into them.

— Kim Ann Zimmermann

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