Science / Astrology / Co-Ruler: Prior to the discovery of Uranus, the Sun and Moon were believed to rule one sign each and the other five planets then known to humankind (Mercury through Saturn) to rule two signs each. When the three outermost planets were discovered, they became co-rulers of the signs Aquarius (Uranus), Pisces (Neptune) and Scorpio (Pluto), along with the traditional rulers, Saturn, Jupiter, and Mars respectively. Modern studies seem to indicate that the new co-rulers are primary rulers of the signs with which they are associated and may be sole rulers, in which case, two other planets, one linked to Libra (or Taurus) and the other to Virgo, may await discovery, thus eliminating dual rulership. Co-rulership of a house is shared by planets that rule the sign on the cusp and any sign intercepted within the house and planets occupying that house.