In astrology, a planet's domicile is the zodiacal sign over which it has rulership. This is a separate concept from the houses of the horoscope. A planetary ruler is given to each sign, over which the planet is said to have a more powerful influence when positioned therein. The ruling planet associated with a sign is also used as an implied focus of interpretation for the signs on house cusps in a chart. A planet is considered to be in domal dignity when it is positioned in the sign it rules. This is the strongest of the five essential dignities of a planet. Domicile is an archaic term in infrequent, specialist uses today; most astrologers use the simpler term "sign".

Sagittarius (♐︎) is the ninth astrological sign, which is associated with the constellation Sagittarius and spans 240–270th degrees of the zodiac. Under the tropical zodiac, the sun transits this sign between approximately November 22 and December 21. Greek mythology associates Sagittarius with the centaur Chiron, who mentored Achilles, a Greek hero of the Trojan War, in archery.