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.

[3] The official constellation boundaries, as set by Belgian astronomer Eugène Delporte in 1930, are defined by a polygon of 3 main and 7 western edgework forming sides (illustrated in infobox).

It has a faint magnitude 14 red dwarf companion located 29 arcseconds away that takes 76,000 years to complete an orbit.

Known as Asellus Borealis "northern donkey", Gamma Cancri is a white-hued A-type subgiant of spectral type A1IV and magnitude 4.67,[12] that is 35 times as luminous as of the Sun.

Despite having different distances when measured by the HIPPARCOS satellite, the two stars share a common proper motion and appear to be a natural binary system.

The red dwarf 55 Cancri B, a suspected binary, appears to be gravitationally bound to the primary star, as the two share common proper motion.

Praesepe is also one of the larger open clusters visible; it has an area of 1.5 square degrees, or three times the size of the full Moon.

The stars represent the donkeys that the god Dionysus and his tutor Silenus rode in the war against the Titans.

The ancient Chinese interpreted the object as a ghost or demon riding in a carriage, calling it a "cloud of pollen blown from under willow catkins.

"[citation needed] The smaller, denser open cluster Messier 67 can also be found in Cancer, 2600 light-years from Earth.

[1] QSO J0842+1835 is a quasar used to measure the speed of gravity in VLBI experiment conducted by Edward Fomalont and Sergei Kopeikin in September 2002.

[citation needed] Dante, alluded to its faintness in Paradiso, and mentioned it being visible for the whole night when it culminated at midnight in a Northern Hemisphere winter month: Cancer was the backdrop to the Sun's most northerly position in the sky (the summer solstice) in ancient times, when the Earth's Sun-facing side was maximally tilted towards the south, in the Gregorian calendar kept within a few days of June 21.

[1] The close conjunction of Jupiter and Saturn in 1563 – which was observed by Tycho Brahe and led him to note the inaccuracy of existing ephemerides and to begin his own program of astronomical measurements – occurred in Cancer not far from Praesepe.

In Greek mythology, Cancer is identified with the crab that appeared while Heracles fought the many-headed Lernaean Hydra.

On boundary stones, the image of a turtle or tortoise appears quite regularly and it is believed that this represents Cancer since a conventional crab has not so far been discovered on any of these monuments.

A 1488 Latin translation depicts cancer as a large crayfish,[23] which also is the constellation's name in most Germanic languages.

In Chinese astronomy, the stars of Cancer lie within the Vermilion Bird of the South (南方朱雀, Nán Fāng Zhū Què).