In Hindu tradition, Rahu is the severed head of an asura called Svarbhanu, that swallows the sun causing eclipses. He is depicted in art as a serpent with no body riding a chariot drawn by eight black horses. Rahu is one of the navagraha (nine planets) in Vedic astrology and is paired with Ketu
Rahu and Ketu is considered as two strong planets as per the principles of Vedic Astrology. But astronomically, they do not exist. Since Rahu and Ketu are believed to have a strong impact on our lives, they are denoted as mathematical points while making calculations in Vedic Astrology.
When Moon moves from South to North in its orbit and crosses Sun's path - the incision point is called Rahu or Dragon's Head. When Moon transits towards South and crosses the Sun's path - the incision point is called Ketu or Dragon's Tail. This point is at 180 degree distance from the previously mentioned incision point (Rahu).
In Vedic Astrology, Rahu and Ketu are given high importance. But why? Why are these incision points considered so important? The general explanation is that Sun represents body whereas Moon represents mind and these incision points strongly affect the energies of these two planets.
Rahu and Ketu are not stationary. In a year, they move 19 degrees and 30 minutes which means that Rahu and Ketu take 18 years and 6 months to complete 1 round around Earth. These two planets transit in retrograde motion (in opposite direction to all other planets).
Mythology about Rahu and Ketu
This story relates to the great churning of the ocean by theGods and the Demons to take out elixir of life. Lord Vishnu wanted to ensure that the elixir did not reach the hands of the Demons. If they caught hold of the potion, they would destroy the world, Lord Vishnu feared. So, Lord Vishnu took the form of Mohini. Mohini so maneuvered the sitting arrangement that she got to the Gods first. The demon to catchthis trick was Swarbhanu. He took the form of a god and positioned himself in between Sun and Moon. When his term came he also received elixir from the disguised Lord Vishnu. BeforeSwarbhanu could drink the elixir Sun and Moon identified him. Lord Vishnu severed off his head with Sudarshan Chakra. However, some drops of elixir of life had gone down his neck hence both the head and body became immortal.
The severed head was taken bySimihika, the mother of demonSwarbhanu, and nursed patiently. The head over a period of time got the body of a serpent and he was named Rahu. A Brahmin named Mini took the body. He brought up this body as his own son. To this body Lord Vishnugranted a serpent's head. This became Ketu who in the due course of time became a saintly and revered seer.
However, Rahu and Ketu never pardoned Sun and Moon for exposing them. Therefore, they cause eclipses.
Rahu is considered to be Swagruhi (in its own House) when it is in Virgo. It is exalted when placed in Taurus while it is debilitated when in Scorpio. However, there are divergent views on this. Some authorities take the Exaltation and Debilitation points as Gemini and Sagittarius respectively. It is said that Rahu gives Yogkaraka result if it is in Cancer. However, it has to be noted that being a Shadow planet (Chhaya Grah) it gives results based on other planetary influences. It is generally observed that with a benefic or in benefic influence it gives very good result. It is generally considered as a good planet for worldly comforts. However, Rahu also signifies delusions and vanity. In modern times Rahu represents Computers, Internet and Mass Media.
Rahu is friendly to Jupiter, Venus and Saturn. It considers Sun and Moon as its enemies and towards Mercury it is Neutral.
Ketu is exalted in Scorpio and debilitated when in Taurus. However, some astrologers have given the Exaltation and Debilitation points as Sagittarius and Gemini respectively. It has to be said that Ketu is more towards spiritual side and is the Karaka for final emancipation whereas Rahu is more towards worldly pleasures. Again it has to be said that being a Shadow planet (Chhaya graha) Ketu gives results according to associations with other planets in a Kundali.
However, in spite of having number of ancient texts extensively dealing with various signs of exaltation and debilitation of Rahu and Ketuthere exists significant amount of controversy over the same.
Ketu is friendly to Mars, Venus and Saturn. It considers Sun and Moon as his enemies and towards Mercury and Jupiter it is Neutral.