Cancer is one of the twelve constellations of the zodiac and is located in the Northern celestial hemisphere. Its name is Latin for crab and it is commonly represented as one. Cancer is a medium-size constellation with an area of 506 square degrees and its stars are rather faint, its brightest star Beta Cancri having an apparent magnitude of 3.5. It contains ten stars with known planets, including 55 Cancri, which has five: one super-Earth and four gas giants, one of which is in the habitable zone and as such has expected temperatures similar to Earth. At the (angular) heart of this sector of our celestial sphere is Praesepe (Messier 44), one of the closest open clusters to Earth and a popular target for amateur astronomers.
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👉 Cancer (constellation) in the context of Star cluster
A star cluster is a group of stars held together by self-gravitation. Two main types of star clusters can be distinguished: globular clusters, tight groups of ten thousand to millions of old stars which are gravitationally bound; and open clusters, less tight groups of stars, generally containing fewer than a few hundred members.
As they move through the galaxy, over time, open clusters become disrupted by the gravitational influence of giant molecular clouds, so that the clusters we observe are often young. Even though they are no longer gravitationally bound, they will continue to move in broadly the same direction through space and are then known as stellar associations, sometimes referred to as moving groups. Globular clusters, with more members and more mass, remain intact for far longer and the globular clusters observed are usually billions of years old.
In this Dossier
- ⭐ Core Definition: Cancer (constellation)
- 👉 Cancer (constellation) in the context of Star cluster
- Cancer (constellation) in the context of Cancer (astrology)
- Cancer (constellation) in the context of Messier 44
- Cancer (constellation) in the context of Constellation of Leo
- Cancer (constellation) in the context of Hydra (constellation)
Cancer (constellation) in the context of Cancer (astrology)
Cancer (♋︎; Ancient Greek: Καρκίνος, romanized: Karkínos, lit. 'crab', Latin for the "Crab") is the fourth astrological sign in the zodiac, originating from the constellation of Cancer. It spans from 90° to 120° celestial longitude. Under the tropical zodiac, the Sun transits this area between approximately June 22 and July 23.
In astrology, Cancer is the cardinal sign of the Water trigon, which is made up of Cancer, Pisces, and Scorpio. It is one of the six negative signs, and its ruling planet is the Moon. Though some depictions of Cancer feature a lobster, crayfish, scarab beetle or a turtle, the sign is most often represented by the crab, based on the Karkinos. Cancer's opposite sign is Capricorn.
Cancer (constellation) in the context of Messier 44
The Beehive Cluster (also known as Praesepe (Latin for "manger", "cot" or "crib"), M44, NGC 2632, or Cr 189) is an open cluster in the constellation Cancer. One of the nearest open clusters to Earth, it contains a larger population of stars than other nearby bright open clusters holding around 1,000 stars. Under dark skies, the Beehive Cluster looks like a small nebulous object to the naked eye, and has been known since ancient times. Classical astronomer Ptolemy described it as a "nebulous mass in the breast of Cancer". It was among the first objects that Galileo studied with histelescope.
Its age and proper motion coincide with those of the Hyades, suggesting they may share similar origins. Both clusters also contain red giants and white dwarfs, which represent later stages of stellar evolution, along with many main sequence stars.
Cancer (constellation) in the context of Constellation of Leo
Leo /ˈliːoʊ/ is one of the constellations of the zodiac, between Cancer, the Crab, to the west and Virgo, the Maiden, to the east. It is located in the Northern celestial hemisphere. Its name is Latin for lion, and to the ancient Greeks represented the Nemean Lion killed by the mythical Greek hero Heracles as one of his twelve labors. Its old astronomical symbol is 
(♌︎). One of the 48 constellations described by the 2nd-century astronomer Ptolemy, Leo remains one of the 88 modern constellations today, and one of the most easily recognizable due to its many bright stars and a distinctive shape that is reminiscent of the crouching lion it depicts.
Cancer (constellation) in the context of Hydra (constellation)
Hydra is the largest of the 88 modern constellations, measuring 1303 square degrees, and also the longest at over 100 degrees. Its southern end borders Libra and Centaurus and its northern end borders Cancer. It was included among the 48 constellations listed by the 2nd century astronomer Ptolemy. Commonly represented as a water snake, it straddles the celestial equator.