Graha (Planet) literally means ‘to affect’. Grahas are astrological bodies which have a direct or indirect effect on everything in the entire universe, whether alive or inanimate.
In Hindu spiritualism, Navgrahas (9 planets) hold a special significance; they are Surya (Sun), Chandra (Moon), Mangal (Mars), Budh (Mercury), Guru (Jupiter), Shukra (Venus), Shani (Saturn), Rahu and Ketu. Of these, 7 are real planets while Rahu and Ketu are considered as shadow planets.
The speed of the planets and their effectss are a part of the study of Jyotish (astrology). The most ancient astrological science in India is called Vedang Jyotish.
Hinduism considers Grahas as divine powers whose happiness or wrath has an effect on humans accordingly. Therefore, every believer wishes for their happiness and favourability.
Every Graha is considered as the lord of different Nakshatras (27 of them), and the star sign (12 of them) on which they have the greatest effect is considered as their own star sign.
A worship of these Navgrahas is considered as a must by Hindus before commencing any auspicious event. Navgraha Temples are also seen at various places in India. In fact, the Shiv Temples in Southern India have a specific place assigned to them. It is believed that the planets were formed due to the Rudra (furious) form of Shiv.
Several ancient texts have considered these Navgrahas as a part of the 9 incarnations of Vishnu; Shri Ram (Surya), Shri Krishna (Chandra), Narsingh (Mangal), Buddha (Budh), Vaman (Guru), Parshuram (Shukra), Kurm (Shani), Varah (Rahu), and Matsya (Ketu).
Belief in the effect of the Grahas and their worship is prevalent among Jains and Buddhists too apart from the Hindus.
Western astrology, which is largely influenced by the Greek astrology, also believes in the effect of the Grahas. However the names of the Grahas and their actions are different from Indian astrology in various aspects.
In the Indian spiritualism, these Grahas are believed to have not only their own respective colours, vehicles, gems, and directions but also Gods and sub-Gods and following the right ones bring about a positive effect of these Grahas