Cancer is the fourth sign of astrology in the zodiac, which originated in the cancer constellation. It spans 90 ° and 120 ° longitudes. Under the tropical ecliptic, the sun passes through the region between June 21 and July 23. Under the stellar ecliptic, the sun passes through the region between July 16 and August 15.

In astrology, cancer is the basic symbol of the water triangle. It consists of cancer, Pisces and Scorpio. It is considered to be a minus sign whose home or ruling planet is the moon. Although some depictions of cancer have lobsters, the sign is often represented by crabs based on karkinos, a type of cancer that harasses Heracles in the fight against Hydra.