Cancer (constellation) in the context of Messier 67

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.

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.

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.

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.

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.

Cancer also known as Carcinus (Ancient Greek: Καρκίνος, romanized: Karkínos, lit. 'crab') or, simply the Crab, is a giant crab in Greek mythology that inhabited the lagoon of Lerna. He is a secondary character in the myth of the twelve labors of Heracles, who attacks Heracles on Hera's orders, while Heracles is in the midst of fighting the Hydra of Lerna. Heracles kills the Crab, who is rewarded for his efforts by Hera turning him into the constellation of Cancer.

Since it is not a main element of the myth, it does not always appear in the versions that have reached the present day; nevertheless, classic mythographers, astronomers, historians or philosophers such as Plato, the Pseudo-Eratosthenes, Apollodorus and Hyginus mention the character in their texts.

Pushya (Sanskrit: पुष्य), meaning "the nourisher", is the 8th nakshatra (lunar mansion) in Indian astronomy. Some texts refer to it as Tishya, meaning "to look". It corresponds to the stars γ, δ, and θ Cancri in the constellation Cancer, which surround the Beehive Cluster (Praesepe, M44). Its appearance is described in Indian star catalogs as meghavt "cloudy", referring to the star cluster. Pushya is known as Pushyami (పుష్యమి) in Telugu, Poosam (பூசம்) in Tamil, and Pooyam (പൂയം) in Malayalam.

Beta Cancri is the brightest star in the zodiacal constellation of Cancer. The star has the proper name Tarf, pronounced /ˈtɑːrf/; Beta Cancri is its Bayer designation. It is visible to the naked eye with an apparent visual magnitude of +3.5, and has an absolute magnitude of −1.2. Based on parallax measurements, it is 303 light-years distant from the Solar System. It is drifting further away with a line of sight velocity of 23 km/s. An exoplanet, designated Beta Cancri b, is believed to be orbiting the star.

Beta Cancri has a visual companion listed and together they are designated WDS J08165+0911. However, it is not certain if the companion is gravitationally bound or not. As the primary, Beta Cancri bears the designation WDS J08165+0911A. The companion is designated WDS J08165+0911B.

55 Cancri is a binary star system located 41 light-years away from the Sun in the zodiac constellation of Cancer. It has the Bayer designation Rho Cancri (ρ Cancri); 55 Cancri is the Flamsteed designation (abbreviated 55 Cnc). The system consists of a K-type star (designated 55 Cancri A, also named Copernicus /koʊˈpɜːrnɪkəs/) and a smaller red dwarf (55 Cancri B).

As of 2025, four extrasolar planets, designated 55 Cancri Ab, Ac, Ae and Af, named Galileo, Brahe, Janssen, and Harriot, respectively, and two planet candidates 55 Cancri Ad (named Lipperhey) and 55 Cancri Ag are known to orbit 55 Cancri A; alongside two extrasolar planets, designated Bb and Bc, which are known to orbit 55 Cancri B.