What is Rulership / Domicile?
Rulership (or domicile) is the strongest essential dignity. Each planet rules one or two signs: Sun rules Leo, Moon rules Cancer, Mercury rules Gemini and Virgo, Venus rules Taurus and Libra, Mars rules Aries and Scorpio, Jupiter rules Sagittarius and Pisces, and Saturn rules Capricorn and Aquarius. A planet in its own sign functions with complete authority—it sets the rules, feels at home, and expresses its nature without friction or compromise.