Found on the cusp of the 1st house (the ascendant or rising sign, or the 'Western directional Point' of the compass), the Chart Ruler has a unique emphasis because it sets the pace for the energy of the psyche as displayed in the chart's placement of planets and signs. It truly is "the Key" that unlocks the chart.
(*And yes: some planets have more than one sign under its rulership. This hopefully will be corrected as more planets are identified.
It is also mentioned by key astrologers that the Earth should rule Taurus, or that the asteroid Juno should rule Libra. This duality of rulerships came about partially because the early origins of the zodiac did not include the outer planets beyond Saturn.)
The Chart Ruler's sign follows the zodiac rulership as follows:
Aries is ruled by Mars, and co-ruled by Pluto.
Taurus is ruled by Venus.
Gemini is ruled by Mercury.*
Cancer is ruled by the Moon.
Leo is ruled by the Sun.
Virgo is ruled by Mercury.*
Libra is ruled by Venus.
Scorpio is ruled by Pluto, and co-ruled by Mars.
Sagittarius is ruled by Jupiter.
Capricorn is ruled by Saturn.
Aquarius is ruled by Uranus, and co-ruled by Saturn.
Pisces is ruled by Neptune, and co-ruled by Jupiter.
Once the (primary) ruling planet is identified, consider the qualities of that planet. Then look at the house (or "Area of Life Experience") where it is located. That area is a primary emphasis of the psyche above and beyond all other houses, planets, and signs in the chart. As an example, my chart has Virgo rising, therefore my chart ruler is Mercury, Indicator of Mental Abilities and Communications. It's found in the 7th house of Partnerships & Relationships--which is my primary influence.
By learning the signs, planets, and house meanings, it becomes very easy to pick out the Chart Ruler in anyone's horoscope!
