Cancer, the Crab, is a zodiacal constellation that lies on the ecliptic between Gemini and Leo. Hold your mouse cursor over the image to see constellation figures, boundaries, and star identifications. In Greek mythology, the goddess Hera sent the crab to distract the hero Hercules while he was fighting the Hydra, a beast with many serpent-like heads during the 12 labors of Hercules. In different versions of the story, Hercules either kicks the crab into the night sky, or he kills it and Hera places it in the sky. Cancer is the faintest zodiacal constellation. None of the stars in Cancer are brighter than magnitude 3.5. Alpha Cancri is Acubens, which is only the fourth brightest star in the constellation. It is a spectral-class A-type variable star that varies in apparent magnitude from 4.2 to 4.27. It is located 274 light-years away from the Earth. Acubens is really a tight double star with 5.0 magnitude components separated by 0.1 arcseconds. It also has an 11.8 magnitude companion separated by 11 arcseconds. Beta Cancri, Al Tarf, is the brightest star in Cancer, shining at magnitude 3.5. It is a spectral-type K yellow giant that lies 290 light-years from Earth. Cancer contains two Messier objects, open cluster Messier 44, the Praesepe or Beehive Cluster, and the open cluster Messier 67. M44 is easy to spot from a dark-sky location, shining at magnitude 3.7 and covering more than a degree of sky. Because it lies on the ecliptic, Cancer can host bright planets such as Jupiter, Saturn, Venus and Mars. The ecliptic is the path that the Sun, Moon and planets follow across the sky. As we move into Cancer, we start to move into the springtime sky as the winter Milky Way heads toward setting in the west. Leo and the spring constellations will follow. The Sun is located in the constellation of Cancer from July 20 to August 10. Cancer was cataloged by the Greek astronomer Ptolemy in the second century C.E. (Common Era). It is the 31st largest of today's 88 modern constellations, covering 506 square degrees of sky. North is to the top in the above image.
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