According to Hindu Astrology, the life of all human beings is influenced by the 9 Planets or Navagrahas. The 9 planets considered by Vedic astrologers are the Sun, Moon, Mars, Mercury, Jupiter, Venus, Saturn, Rahu and Ketu. The outer planets of Neptune, Uranus, and Pluto are not used in ancient classical Vedic astrology and thus have no gemstones assigned to them. The main gems for these 9 planets referred to as "navaratna" meaning 9 gems and the substitute gems are called "uparatna". This influence the planets may be positive or negative. Based on an individual's horoscope or position of Planets, either a single gem or a combination of compatible gems is advised to be worn to increase the effects of beneficial planets or counteract harmful planets.