In astrology, Rahu-Ketu is kept in the category of shadow planet and Rahu-Ketu is seen in the form of an inauspicious planet, all are afraid of them. Both of these planets are considered very effective. The moon and the sun are eclipsed by Rahu-Ketu itself.
It is famous for the story that no one could kill Raja Harikyakshyap, for protecting him and his son Lord Vishnu had to incarnate as Narasimha. Raja Harikyakashyap’s daughter Sinhala married Vipriti Achure, both of whom had a son named Rahu or Swarabhanu, Rahu was inseparable.
It is widely believed that Kshirsagar was churned for obtaining nectar in Deities and Asura, and after this churning, Maharishi Dhanvantri came out with a nectar of Kalash and he also brought 14 gems with him.
Lord Vishnu binded the asuras into temptation and gave them nectar to gods, Rahu sat in the middle of the sun and moon. Vishnu became angry and separated Rahu’s head from the trunk, but by then Rahu had drank nectar and he became immortal. The head was kept and the torso was given the name of Ketu.
According to one belief Rahu received the head of the serpent and the head of the serpent to Ketu, that is why Rahu and Ketu hate the sun and the moon and accept it, and thus show their hostility towards them.