Each of the zodiac signs has a planetary ruler - a planet which is said to function strongly and be particularly comfortable and 'at home' in the sign. The planetary rulers of the signs were allocated by the Greeks in a symmetrical and balanced proportion, with each planet having rulership over two signs, one positive and one negative, except for the Sun and Moon, which each have rulership over only one sign. The planetary rulers are distributed evenly amongst the signs in order of their observed distance from the earth, as shown in the diagram.

The Sun has rulership over the sign of Leo, the hottest time of the year when the Sun is at the height of its strength. The Moon has rulership over the sign of Cancer, which begins with the Summer Solstice, marking the Sun's change of direction. Moving outwards in decreasing orbital speeds, Mercury comes next, and has rulership over both the signs of Gemini and Virgo. Then comes Venus, ruling both the signs of Taurus and Libra, then Mars which rules Aries and Scorpio, then Jupiter which rules Pisces and Sagittarius. Finally, at the coldest and darkest time of the year, Saturn as the slowest planet, has rulership over the signs of Aquarius and Capricorn. The outer planets are relatively recent newcomers and have been added to this model: Pluto as the modern ruler of Scorpio, Uranus as the modern ruler of Aquarius and Neptune as the modern ruler of Pisces.

"Mapping the Psyche"