The Celestial Crab

Cancer, known as the Celestial Crab, is a constellation in the Zodiac that is rich in history and celestial treasures. Despite its somewhat faint appearance in the night sky, Cancer houses intriguing deep-sky objects, including one of the sky's most spectacular open clusters, the Beehive Cluster (Messier 44).

Historical Background

Like all the Zodiac constellations, the history of Cancer dates back to ancient times. The constellation was first cataloged by the Greek astronomer Ptolemy in the 2nd century. Its association with the crab comes from Greek mythology, where it was placed in the sky by the goddess Hera to commemorate its efforts in the battle between the Lernaean Hydra and Hercules.

Location and Notable Features

Cancer is located in the second quadrant of the Northern Hemisphere (NQ2) and is visible at latitudes between +90? and -60?. Bordered by Gemini to the west and Leo to the east, it is one of the smaller constellations, ranking 31st in size.

Despite its historical significance, Cancer is relatively faint, with its brightest star, Beta Cancri or Altarf, having an apparent magnitude of just 3.5. Nevertheless, the constellation's distinctive inverted "Y" shape is discernible in clear, dark skies.

Deep Sky Objects

While it may lack in brightness, Cancer is far from lacking in celestial wonders. Its jewel is the Beehive Cluster, also known as Messier 44 or Praesepe. This open cluster, visible to the naked eye in good conditions, has an apparent magnitude of 3.7 and is one of the nearest open clusters to Earth, at a distance of about 577 light-years. Galileo Galilei was the first to observe the Beehive Cluster via telescope in 1609, identifying 40 stars.

Another noteworthy deep-sky object is Messier 67, an open cluster of about 500 stars. Estimated to be around four billion years old, it's one of the oldest open clusters known. Despite being fainter and less famous than the Beehive Cluster, M67 is a favorite target for astronomers due to its age and high population of stars.

Observing Cancer

For observers in the Northern Hemisphere, Cancer is best seen in late winter and early spring. The constellation's relatively faint stars make it a challenging but rewarding target for naked-eye observers under dark skies. The Beehive Cluster and M67, however, are best viewed with binoculars or a small telescope.

* Constellation shown for northen hemisphere skies. For the southern hemisphere, constellations appear rotated 180 degrees (upside-down and left-right reversed) from what is shown. Remember that seasons are reversed too - summer in northern latitudes is winter in southern latitudes.

** Circumpolar constellations are visible year-round in the hemisphere listed (and not at all in the opposite hemisphere).