Rahu and Kethu are imaginary planets or shadowy planets and they are points of intersection of the orbits of Sun and Moon and therefore have no exaltation and debilitation points. Generally they inherit the qualities of the lord of the house in which they are placed. There are many mythical qualities for Rahu and Kethu as per the whims of wayside astrologers available on the internet very similar to Guru Chandal Yoga.
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