Rahu, also called Tamas, is the cut off head of an asura who drank some of the amrita or soma. The sun and the moon realized it and they alerted Mohini (the female avatar of Vishnu). Before the nectar could pass his throat, Mohini cut off his head. The head, however, remained immortal due to the effect of amrita and became Rahu. It is believed that this immortal head from time to time swallows the sun, causing eclipses.
Rahu is a shadow planet i.e. it doesn’t have any physical identity but it is signified by certain sensitive points in one’s planetary chart.
The planet Rahu relates to mind, insanity, epilepsy, fights and trifles. Our astrologers understand that a malefic Rahu or Rahu Mahadasha can cause various troubles such as poverty,