Rahu and Ketu have been considered as Grahas in Vedic astrology. They have no physical identity but only mathematically calculated sensitive points having immense influence on the natives of earth.
Moon in its orbit, on a northerly course from South to North, crosses the ecliptic (the apparent path of Sun). This point of intersection is known as Rahu or Dragons head. 180 degrees away from this point, Moon on its southerly course crosses the ecliptic. This point is called the dragon's tail or Ketu.
Rahu and Ketu are unique to our system or astrology. Why so much stress on the point of intersection of the ecliptic is given has to be understood. While sun is the body and Moon is the mind the intersection is bound to give immense effect.
Rahu and Ketu are not stationary in space but have a mean motion of about 19 degrees and 30 minutes in a year. It means it takes about 18 years and 6 months to make a revolution around the Earth. This motion is retrograde. There is a concept of Mean Rahu and True Rahu. In Hindu astrology we take the true position of Rahu and Ketu.
Mythology:
This story relates to the great churning of the ocean by the Devas and the Asuras to take out Amrita. Lord Vishnu with the intention of preserving good made it a point that the Amrita should not go to the Asuras. To ensure this he took the form of Mohini. Mohini so maneuvered the sitting arrangement that she got to the Devtas first. The Asura to understand this trick was Swarbhanu. He took the form of Devas and positioned himself in between Sun and Moon. When his term came he also received Amrita from the disguised Lord Vishnu. Before Swarbhanu could drink the Amrita Sun and Moon identified it. Lord Vishnu severed off his head with his Sudarshan Chakra. However, some drops of Amrita had gone down hence both the head and body became immortal. The head represents Rahu and Tail is Ketu.
The severed head was taken by Simihika the mother of Asura Swarbhanu and nursed patiently. The head over a period of time got the body of 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 Vishnu granted a serpents head. This became Ketu who in the due course of time became a saintly and revered seer.
Rahu and Ketu have not forgiven Sun and Moon for exposing them and they cause Eclipse.
Astrological Significance:
Rahu:
Rahu is the significator of the following as per Uttara Kalamrita.
a) Faulty Logic b) Harsh speech c) Outcaste d) an irreligious person e) going to a foreign country f) Unclean g) Bones h) abdominal ulcers i) Falsehood j) South western direction k) serpents l) Old age m) Maternal grand father n) Worship of Vana Durga o) Writing Urdu or Persian (Because these two languages start from right hand side, written in reversed manner, like Rahu and Ketu's movement in Zodiac, which is retrograde or Apsavya move. p) Breathing q) Acute duodenal pain.
It is observed that a strong Rahu is good for the above mentioned significations and weak Rahu shows just the opposite.
Ketu:
Ketu is the significator of following as per Uttara Kalamrita
a) Worship of Chandi, Ganesh and others b) Medical practitioner c) Vultures d) Final emancipation e) Consumption f) Painful fevers g) Bath in Gangesh h) Great penance i) Wind complaints j) Mantra Shastra k) Instability of mind l) Diseases of the stomach and eye m) Vedanta n) Grandfather o) Small pox or boils p) A servant of Shiva q) Association with foreigner or Shudras.
It is observed that a strong Ketu generally gives good result and a malefic Ketu creates lots of hindrances in life.
Other Astrological Considerations:
Rahu:
Rahu is in own house in Kanya Rashi. It is exalted when placed in Vrishabha Rashi while it is debilitated when placed in Vrischik Rashi. However, there are divergent views on this. Some authorities take the Exaltation and Debilitation points as Mithuna and Dhanu respectively. It is said that Rahu gives Yogkaraka result if placed in Cancer Karkata Rashi. However, it has to be noted that being a Chhaya Grah it gives results based on the 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, there is lots of Maya attached with Rahu. 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 enemy and towards Mercury it is Neutral.
Ketu:
Ketu is exalted when it is placed in Scorpio Vrischik rashi and debilitated when placed in the Vrishabha Rashi. However, some authorities have given the Exaltation and Debilitation point as Dhanu and Mithuna 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 Chhaya Graha gives results according to associations.
However, in spite of having number of ancient texts extensively dealing with various signs of exaltation and debilitation of Rahu and Ketu there 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.
