The zodiacal attribution for the 18th path of the qabalistic Tree of Life is the sign of the Crab, Cancer. Its name is Latin for crab and it is commonly represented as such. Its symbol is . Cancer is small and its stars are faint. It lies between Gemini to the west and Leo to the east, Lynx to the north and Canis Minor and Hydra to the south. 55 Cancri is a quintuple planet system with four gas giants and one terrestrial planet which has temperatures likely to allow the existence of liquid water and potentially the conditions to sustain life. Cancer is also the fourth astrological sign in the Zodiac. It is considered a water sign and one of four cardinal signs. Cancer is ruled by the Moon. Individuals born when the Sun is in this sign are considered Cancerian individuals. Under the tropical zodiac, the Sun enters Cancer on the moment of summer solstice by definition, or roughly on June 21, leaving it around July 21. Cancer is said to have been the place for the Akkadian Sun of the South, perhaps from its position at the summer solstice in very remote antiquity. But afterwards it was associated with the fourth month Duzu (June–July in the modern western calendar), and was known as the Northern Gate of Sun. Showing but few stars, and its brightest stars being of only 4th magnitude, Cancer was often considered the “Dark Sign”, quaintly described as black and without eyes. In the Egyptian records of about 2000 BC it was described as Scarabaeus (Scarab), the sacred emblem of immortality. In Babylonia the constellation was known as MUL.AL.LUL, a name which can refer to both a crab and a snapping turtle. On boundary stones, the image of a turtle or tortoise appears quite regularly and it is believed that this represent Cancer as a conventional crab has not so far been discovered on any of these monuments. There also appears to be a strong connection between the Babylonian constellation and ideas of death and a passage to the underworld, which may be the origin of these ideas in much later Greek myths associated with Hercules and the Hydra. In the 12th century, an illustrated astronomical manuscript shows it as a water beetle.
Albumasar writes of this sign in the work published in 1489 as a large crayfish. Jakob Bartsch and Stanislaus Lubienitzki, in the 17th century, described it as a lobster. In Ancient Greece, Aratus called Καρκινος (Karkinos), which was followed by Hipparchus and Ptolemy. The Alfonsine tables called it Carcinus, a Latinized form of the Greek word. Eratosthenes extended this as Καρκινος, Ονοι, και Φατνη: the Crab, Asses, and Crib. The Indian language Sanskrit shares a common ancestor with Greek, and the Sanskrit name of Cancer is Karka and Karkata. In Telugu it is “Karkatakam”, in Kannada “Karkataka” or “Kataka”, in Tamil Karkatan, and in Sinhalese Kagthaca. The later Hindus knew it as Kulira, from the Greek Κολουρος (Koloyros), the term originated by Proclus. In Ancient Rome, Manilius and Ovid called the constellation Litoreus (shore-inhabiting). Astacus and Cammarus appear in various classic writers, while it is called Nepa in Cicero’s De Finibus and the works of Columella, Plautus, and Varro; all of these words signify crab, lobster, or scorpion. Athanasius Kircher said that in Coptic Egypt it was Κλαρια, the Bestia seu Statio Typhonis (the Power of Darkness). Jérôme Lalande identified this with Anubis, one of the Egyptian divinities commonly associated with Sirius. Cancer the giant crab, also plays a minor role in the Twelve Labors of Hercules. While Hercules was busy fighting the multi-headed monster, Lernaean Hydra, the goddess Hera, who hated her step-son Hercules, sent the Crab to distract him. Cancer tried to kill Hercules, but Hercules kicked Cancer so hard that the crab was sent into the sky. By other accounts, Cancer grabbed onto the hero’s toe with its claws, but barely breaking the rhythm of his great battle with Hydra, Hercules crushed the crab with his foot. Hera, grateful for the little crustacean’s heroic but pitiful effort, gave it a place in the sky; but none of its stars were bright because the crab had failed to accomplish its given task. Some scholars have suggested that Cancer was a late add-on to the myth of Hercules to make the Twelve Labors correspond to the twelve signs of the Zodiac.
Jeff Mayo, Teach Yourself Astrology, pp 38-41, Hodder and Stoughton, London, 1979.
Dante, alluding to this faintness and position of heavens, wrote in Paradiso:“Then a light among them brightened, So that, if Cancer one such crystal had, Winter would have a month of one sole day.”
Gavin White(2008), Babylonian Star-lore. Solaria Pubs, p. 79-82.