The ruling planet
Every sign has an owner. This is what chains a chart together.
Every sign has a ruling planet: Mars for Aries, Venus for Taurus, and so on. This pairing turns a chart from a pile of separate placements into something connected.
Who rules what
- Aries → Mars · Taurus → Venus · Gemini → Mercury · Cancer → Moon
- Leo → Sun · Virgo → Mercury · Libra → Venus · Scorpio → Pluto
- Sagittarius → Jupiter · Capricorn → Saturn · Aquarius → Uranus · Pisces → Neptune
What it is good for
Here is the useful part: you look at the sign on a house, find its ruler, and see where that planet sits. If Aries is on your second house, your money is tied to Mars, and wherever Mars sits is where the money question actually plays out.
If your rising is Capricorn, who rules your chart?
Capricorn is ruled by Saturn, and the chart ruler is the ruler of the rising sign.