The Navagraha are the nine planetary forces that drive every Vedic chart. Seven are visible bodies: the Sun, Moon, Mars, Mercury, Jupiter, Venus and Saturn. Two are shadow points: Rahu and Ketu, the north and south lunar nodes.
Each graha has a portfolio of life themes. The Sun is the soul and authority; the Moon is the mind and emotional world; Mars is energy and courage; Mercury is speech and commerce; Jupiter is wisdom and fortune; Venus is love and pleasure; Saturn is discipline and endurance. Rahu and Ketu bring obsessions, surprises and karmic lessons.
A planet's strength depends on its sign, house, aspects and the current transit. A well-placed Jupiter can bless education, children and wealth; an afflicted Saturn may teach patience through delay. No planet is purely good or bad — each serves the chart in its own way.
Learning the Navagraha is like learning the alphabet of Jyotish. Once you know the letters, you can begin to read the sentences they form in a birth chart.