Rahu Ketu In Astrology

Rahu and Ketu is the name given to the Nodes of the Moon. Rahu or "Dragon's head" is the North Node and 180 degrees away from this point is the South Node Ketu, also called "the dragon’s tail". In Surya Siddhanta ( book on Astronomy) they are also considered as nodal points which are now known as shadowy planets.
Rahu and Ketu are two of the navagrahas (nine planets) in Vedic astrology. Rahu is a cut-off head of an asura, that swallows the sun causing eclipses. He is depicted as a serpent with no body riding a chariot drawn by eight black horses. The Rahu kalam (time of day under the influence of Rahu) is considered inauspicious specially in southern India.



Some consider Rahu and Ketu aspect like Mars (4, 7 & 8) while some consider like Saturn (3, 7, & 10) and others consider like Jupiter (5, 7 & 9th). Some astrologers says that they have just 7th aspects, generally (5, 7 & 9th) aspect theory is more popular.

Rahu 

In ancient time Rahu was considered as the Curse in the Horoscope if not placed well, but in kalyuga it is considered as most powerful planet if well placed it bestows very good results in materialistic sense. Most of it's qualities are same as Shani and other characteristics are as follows Shadow, Darkness, Night, Blackness, Hypnosis, Vashikaran, Gambling, Extreme Tantra like Jaran Maran, Horrifying, Aghor, Diseases, Madness, Calamities, Loss of Sight, Blindness, Disabilities of Body etc are under Rahu Ruler Ship.
  •  The Southwest direction is given to the rulership of Rahu. 
  •  The age of 42 is considered to be the time in which Rahu comes to full fruition. 
  •  Rahu is malefic as a whole though he does bring about the tendency of being "lucky". 
  •  Black color and color of "smoke" are associated with Rahu as well as the color . 
  •  His metal is Lead, like Ketu. The wind or air is considered the element of Rahu. Rahu has a Vatta constitution in Ayurveda.
Ketu
  • Ketu is associated with the god Brahma and Chitra Gupta. Another popular affiliation is Ganesha, which seems more intuitive considering he is known as the "remover of obstacles". 
  •  Ketu has an unusual association in terms of direction.
  •  He is most often noted to be the "center" which is really no direction at all.
  •  Ketu is associated with the 48th year of life. Ketu is extremely malefic though the affliction it gives brings about enlightenment and spiritual growth. 
  • Turquoise and Cats eye are associated with Ketu. Earth is considered the element of Ketu.

Many ancient astrologers believe Rahu and Ketu do not own any signs, but some say Rahu owns lordship of Aquarius and ketu is the lord of Scorpio, according to Parashar, Rahu is exalted in Taurus and Ketu in Scorpio. Cancer is Mooltrikona and Virgo is own sign of Rahu but for Ketu Gemini is Mooltrikona and Sagitattarius and Pisces are his own signs. Rahu and Ketu own nakshatras, and hence are assigned appropriate dasha periods in the Vimshottari dasha system. Rahu owns Ardra, Swati and Shatabisha and has 18 years of Vimshottari dasha. Ketu owns Ashvini, Magha and Moola nakshatras and has 7 years out of 120 years of Vinshottari dasha period. In this way if Tauras is the sign of exaltation for Rahu, the 7th Scorpio is his sign of debilitation.