Ruling planet, in full
The classical table uses the seven bodies visible without a telescope and is perfectly symmetrical. Ptolemy sets it out in the Tetrabiblos: Leo to the Sun and Cancer to the Moon, the pair of signs at the height of northern summer, then the other five planets taking two signs each, one stepping down from Cancer and one stepping up from Leo. Mercury has Gemini and Virgo, Venus has Taurus and Libra, Mars has Aries and Scorpio, Jupiter has Sagittarius and Pisces, Saturn has Capricorn and Aquarius.
The planets found by telescope were fitted into that table afterwards. Uranus was given Aquarius, Neptune was given Pisces, Pluto was given Scorpio. All three signs already had a classical ruler, and a great many astrologers, especially those working in traditional or Hellenistic revival styles, still read Saturn for Aquarius, Jupiter for Pisces and Mars for Scorpio. Plenty of charts list both.
Rulership is a statement of correspondence rather than a claim about physical influence. It decides which planet's condition an astrologer inspects when reading a sign, and it carries through into the number and colour associations attached to signs, because those usually descend from the planet rather than from the sign's own symbolism. Leo's traditional numbers trace back mostly to the Sun, not to the lion.
- Astrology
- Domicile ruler, Sign ruler
A worked example
Mars rules Aries in every version of the table, and Scorpio in the classical one. Mars placed in Aries is read as being in domicile, at home and at full strength. The same planet in Libra, the sign opposite Aries, is called detriment, the weakest of the standard placements, because Libra is Venus's ground rather than Mars's. Modern charts keep the Aries reading and often print Pluto next to Mars for Scorpio.
Sources
The classical rulership table assigns Leo to the Sun and Cancer to the Moon, then gives the remaining five planets two signs each, in order of distance from Earth.
Ptolemy, Tetrabiblos I.17, "Of the Houses of the Several Planets" (Loeb translation, LacusCurtius)
See also
Where it comes up on this site
Ruling planet: frequently asked
Classically: Mars for Aries, Venus for Taurus and Libra, Mercury for Gemini and Virgo, the Moon for Cancer, the Sun for Leo, Mars for Scorpio, Jupiter for Sagittarius and Pisces, Saturn for Capricorn and Aquarius. Modern practice adds Pluto for Scorpio, Uranus for Aquarius and Neptune for Pisces.
Three signs have both a classical and a modern ruler: Scorpio, Aquarius, Pisces. Traditional astrologers never dropped the older assignment, so both stayed in circulation.
No, and astrologers do not generally claim it does.