A keystone in Indian Astrology and mysticism, each Graha carries a specific energy quality and set of mantra, colour, numerical, plants, incense, animal, planetary and god attributions. It is said that the nine planets are transmitters of universal, conventional energy.
Why nine? Well, there are two moons – one for waxing, the other for waning.
Humans are also capable to tune themselves to the chosen energy of a specific Graha through propitiating that Graha or its presiding deity in a prescribed manner.
Traditionally in India most houses will have a nav-grah-ha chowki.