Cancer is the dimmest of the twelve zodiac constellations, and the legend explains why. The crab only has a bit part in the story. It is a tiny creature that stepped into the wrong fight and was crushed under the foot of a hero.
The crab and the Hydra
As the second of his twelve labors, Heracles had to kill the Hydra, a many-headed water serpent that lived in a swamp at Lerna. Hera, who hated Heracles, sent a giant crab to nip at his feet and distract him. He stamped on it and went on with the fight. Hera rewarded the crab for its loyalty by placing it among the stars. The Hydra is in the sky too, and the constellation Hydra runs along the south of Cancer, so the two enemies still sit next to each other.
The gate of souls
In ancient times the sun reached its highest point in the sky, at the summer solstice, while it stood in Cancer. That is why the northern line of latitude where the sun can be directly overhead is called the Tropic of Cancer. Precession has since moved the solstice into Taurus, but the name stuck. Neoplatonist writers, including Macrobius in the fifth century, taught that human souls descend into bodies through the "Gate of Men" in Cancer, and rise back out through the "Gate of the Gods" in Capricorn.
The Beehive
The heart of the constellation is a faint, fuzzy patch called Praesepe, the manger, or the Beehive Cluster. It can be seen with the naked eye on a dark night, and in 1610 Galileo turned his telescope on it and resolved it into dozens of stars. On either side of the manger are two stars called the Aselli, the donkey colts, which in one tale belong to the god Dionysus.
How to find it
To find Cancer, look in spring for a pale gap between Gemini's twin stars and the sickle of Leo. On a dark night, the Beehive Cluster shows up as a small hazy patch there, and binoculars turn it into a swarm of stars. From a city, the whole crab can disappear.
On the star chart
In Hall's chart the crab is drawn in coral orange, spread out across the whole card with its claws raised.
Little-known facts
- Cancer has no star brighter than about magnitude 3.5, so you need dark skies to trace the crab at all.
- The Praesepe cluster contains about a thousand stars and is about 600 light years away.
- The Chinese saw the Beehive as a cloud of ghosts or vapors in the heart of the sky, and named it the "Exhalation of Piled-Up Corpses."
- Cancer is the only sign ruled by the Moon in traditional astrology.
- Cancer 55 e, a planet orbiting a star in this constellation, is a super-Earth whose surface is thought to be hot enough for lava.
Cancer appears on our:
