The navagraha are the nine celestial bodies used in Vedic astrology. Unlike Western astronomy, this includes the luminaries (Sun/Moon), five visible planets (Mars/Mercury/Jupiter/Venus/Saturn), and the two lunar nodes Rahu and Ketu — the north and south nodes of the Moon's orbit. Each graha has a day, a gemstone, a deity, and a set of significations. They are the primary actors in a birth chart and the Vimshottari dasha system assigns each planet a ruling period.