Capricorn is the tenth astrological sign in the Zodiac, originating from the constellation of Capricornus. In astrology, Capricorn is considered an introvert sign, an earth sign, and one of the four cardinal signs. Capricorn is ruled by the planet Saturn. Individuals born when the Sun was in this sign are considered Capricorn individuals. Under the tropical zodiac, the Sun enters Capricorn by definition at the moment of winter solstice, or roughly at December 22, and leaves it around January 20.