Rahu is considered as the negative planet of Solar System. Rahu is translated as materialism and mischief. It is a planet or grah which is related to unconscious desire, fear and uncultured behaviour. It is also considered as an Asura planet.
Rahu came in existence with a very interesting story. When Demigods and Demons became successful to achieve Amrita by doing the Samundra Manthan, it was claimed by the Demons. Demigods then discussed that if Demons became immortal then they will destroy the universe with their negativity. Then Lord Vishnu visited Demons in incarnation of Mohini. Demons infatuated with the beauty of Mohini. Mohini tried to cheat Demons and asked them to drunk Amrita from her hands.
As a result Mohini made them fool and started distributing Amrita among the Demi Gods. An asura named as Svarbhanu was observing all this matter carefully and beside protesting against Mohini. He changed his clothes and wore clothes like Demi Gods. Then he sat in the row of Demi Gods to drink Amrita. God Moon and Sun noticed Svarbhanu and informed Mohini regarding an asura in the row.
But that was too late, Svarbhanu already drunk Amrita and became immortal. In anger Mohini came back to his original form as Lord Vishnu and instructed his Sudarshan Chakra to kill Svarbhanu. But due to Amritapan Swarbhanu didn’t die but his body divided into two parts. One was his head and another was rest of his body. Then his head named as Rahu and body named as Ketu. This is also the reason behind Surya and Chandra grahan, because Surya and Chandra revealed his identity to Mohini.
According to jyotish Shastra Rahu is the owner of Aries and Scorpio zodiac signs. Rahu exalted in Taurus and debilitated in Sagittarius. Rahu stays in one Rashi for 18 years which had a very bad impact on the person with that rashi, this period is known as Vimshottari Mahadasha Period. People who are under Rahu’s mahadasha suffers from Fever, leprosy, snake bite and restlessness. They also believed to suffer from paranormal activities around them.
Rahu also own one of the 8 segments of the day known as Rahu Kala. It is believed as inauspicious period of the day to do good things.