"Chaya Grahas" or "Shadow planets"
There is a fundamental difference between Rahu and Ketu and the other planets. The other planets are bodies of physical mass having form, shape, color, gravity, atmosphere, motion etc. Rahu and Ketu are two imaginary points in the heavens without mass, shape or form. They are the points of intersection of the apparent path of the Sun with the path of Moon. It has been established beyond doubt that Rahu and Ketu influence an individual’s life, at times more than other planets. Since they are in exact opposition to each other, their effect should be considered simultaneously.
Effects
Rahu and Ketu give the effects of the lords of the signs they are in and also of those planets which are situated with them, not having much individual characteristics of their own. Rahu is known as Dragon’s head and Ketu as Dragon’s tail. Head is forward looking while the tail represents the past. The Rahu represents the qualities to be developed and work to be done during the present incarnation and Ketu denotes the qualities during past lives and these indicate stereotypes and attitudes that come naturally to the native. They are classified as Karmic planets. According to Hindu astrology both Rahu and Ketu are malefic. Rahu is considered as ‘giver’ and Ketu the ‘taker’ and since giving and taking are results of former action, they may be considered as planets of "gains and losses". Ketu is considered as a spiritual force causing salvation to human souls and Rahu is more earthly indicating mundane prosperity. The effects of the Nodes is not always evil, they are also productive and causing Raja Yogas. Nodes play a constructive role because after making the native pass through various difficult phases, they also enable him to progress spiritually. However, if the Nodes conjoin Mangala (Mars) or Shani (Saturn) without any benefic aspect, life is marked by misery, struggle and misunderstanding throughout. Rahu is also considered as a diplomat and Ketu a seer.
Rahu and Ketu eclipse the Sun (Surya) and Moon (Chandra) representing the soul and mind respectively. Hence they have a great influence on the soul’s liberation or rebirth. Rahu or Ketu within 2 degrees of the ascendant give an unusual type of personality and a very distinctive appearance. Rahu and Ketu signify one born in low caste, dissatisfied, fond of travelling, telling lie, harsh in speech, involved in unnatural sex. They also indicate change of residence, ill health, dual marriage, serpents, mosquitoes, insects, spices, southwest direction etc. Part of the body represented by them are buttocks, intestinal tract.
Rahu has the properties of Shani (Saturn) whereas Ketu has the influence of Mangala (Mars). Rahu governs paternal grandfather and maternal grandmother. Ketu is eunuch. Ketu is said to be conductive to liberation, Ketu is said to be similar to Mangala (Mars) in giving effects. Ketu rules maternal grandfather and paternal grandmother. Rahu represents the tall while Ketu represents the short persons.
The diseases indicated by them are hiccups, insanity, intestinal problems, ulcer, gastric problems etc.
Products
The products represented by them are meat, wine, eggs, radish, coconut, sacrifice of animal’s etc.