Cancer, which is Latin for "crab", is one of the twelve zodiac constellations and is a rather faint constellation. It was first recorded by Greek astronomer Ptolemy. In Greek mythology, Cancer represents the crab that appeared when Heracles fought the Hydra. This crab appeared and bit Heracles in the foot, after which it was slain.

Despite its faintness, it was historically an important constellation. The close conjunction of Jupiter and Saturn in 1563 occurred in Cancer, and caused Danish astronomer Tycho Brahe to start a program of accurate planetary measurements. This led to astronomers overturning the idea that planets orbited the Sun on perfect circles. Cancer was also the spot of the summer solstice in ancient times. The northernmost line of latitude is still called the Tropic of Cancer today, even though the position of the summer solstice has moved into Taurus.

The named stars, in order of brightness, are:

Tarf (β Cancri), an orange giant star about 303 light years away. It has one planet, about 8 times the mass of Jupiter, orbiting it. Its name comes from the Arabic word Al Tarf meaning "end" or "edge."

Asellus Australis (δ Cancri) is another orange giant star, this one about 137 light years away. Its name is Latin meaning "southern donkey."

Yuyu (ι Cancri) is a double star, likely gravitationally related. One star is a yellow giant star, the other is a blue-white giant, both about 340 light years away. The name comes from the Javanese word hayuyu meaning "freshwater crab."

Acubens (α Cancri) is a binary star system about 178 light years away. The primary star is a blue-white giant star. The name comes from the Arabic al zubanāh meaning "the claws."

Asellus Borealis (γ Cancri) is a solitary blue-white giant star about 175 light years away. Just like its sibling, its name is Latin for "northern donkey."

Tegmine (ζ Cancri) is a quintuple star system about 82 light years away. It consists of several yellow-white Sun-like stars. Its name is the Latin word meaning "the shell."

Nahn (ξ Cancri) is a binary star about 410 light years away. The primary star is a yellow giant star. The name comes from the Persian word nahn meaning "the nose."

Piautos (λ Cancri) is a binary star about 569 light years away, with the primary being a blue giant star. The name comes from the Greek portmanteau of autos meaning "self" and pi- meaning "that." Together, the star's name roughly translates as "the same, the very one."

Copernicus (ρ¹ Cancri) is a binary star system about 41 light years away, consisting of two red dwarf stars. It is named after the Polish astronomer Nicolaus Copernicus, who proposed the heliocentric (sun-centered) model of the solar system. It has four planets orbiting it, all named after other astronomers (Galileo, [Tycho] Brahe) and telescope pioneers ([Hans] Lipperhey and [Zacharias] Janssen).