Rahu is the imaginary planet, the north node of the moon. According to
the Puranas, when the Ocean of Milk was churned, the Nectar of
Immortality was produced. While Lord Vishnu was distributing this nectar
amongst the gods, the celestial serpent demon Rahu mingled amidst the
gods so that he could taste the nectar and attain immortality (Amrita).
The sun and moon gods (Surya and Chandra) saw through Rahu's deception.
When they notified Lord Vishnu, he (Vishnu) cut off Rahu's head in a fit
of rage, but Rahu had already drunk the Nectar and was immortalized.Rahu now refers to the head of the demon. It is also known as 'dragon head'. It is the planet of success. Rahu is associated with the strengthening of personal power. The gemstone of Rahu is hessonite. Rahu causes solar eclipse. Rahu and Ketu are two parts of the same demon.