Ketu is not a physical or celestial entity, but the south node of the two nodes formed when earth`s trajectory around Sun intersects moon`s trajectory around earth. It is a malefic planet, and is always 180 degrees apart from that of Rahu. Ketu and Rahu both are retrograde in motion. Ketu also causes lunar eclipse when Moon, earth and sun aligns in the same longitude along with the node. Ketu is somewhat similar to Mars in nature.

Palasa-puspa-sankasam taraka-graha-mastakam
raudram raudratmakam ghoram tam ketum pranamamy aham.

Ketu is known as "Moksha- Karaka" or the planet influencing spirituality. The person influenced by the planet is usually endowed with psychic powers, healing abilities, excellence in herb logy, tantric, and ghost related ailments. Ketu influences pharmaceutical industry, medicine and astrology to a large extent. Ketu, if favourable, brings a lot of luxury, wisdom and intuition to the person. If unfavourable, it causes weak eyesight, poor concentration, boundless worries and anxiety. According to Hindu mythology, Ketu is the rest of the body of Rahu, while Rahu is the head. When Lord Vishnu extracted the nectar from the ocean, and decided it to give it to the Gods, Rahu (a demon) took the juice and drank in disguise. Rahu was seated between Sun and Moon and they revealed the truth about Rahu`s identity. Lord Vishnu immediately cut the head of Rahu. Since the nectar had reached Rahu`s neck, it survived the ordeal but the rest of the body was burnt. The body was revived again and named as Ketu. Ever since then, Rahu and Ketu are hell bent on taking revenge from Sun and Moon by causing Solar and Lunar eclipse.

Ketu does not rule any zodiac, as it is not a real planet. As oppose to Rahu`s tendency to affect the mind, Ketu inflicts the body. It can cause many types of ailments right from leprosy and cancer to paralysis. Poor blood circulation, Anaemia, pains in joints and nerves are other reaction of this planet. Under common misconception, Ketu is a dreaded planet, bringing with itself disease, sufferings, and dark worlds. But Ketu endows one with supreme form of spiritual enlightenment, which in itself is the greatest boon for human existence.

Ketu`s favourite colour: Smoke
Ketu`s favourite day: Shanivar
Ketu`s favourite gemstone: Cat`s Eye
Ketu`s favourite Deity: Lord Bhairava