Statue of Mohini
(Avatar of Vishnu)
The devas (Gods) can be defined as the beings who drank the amrita (the elixir of eternal life), and the danavas (demons) can be defined as those who were denied the amrita in the primordial age when Samudra Manthana, the churning of the cosmic ocean, took place. Svarbhanu was a special danava—his head drank the amrita, the rest of his body didn’t. He became the progenitor of the two entities, Rahu and Ketu, who have the attributes of both devas and danavas.
The story of Samudra Manthana is given in the Vishnu Purana and several other ancient texts, including the Mahabharata (Adi Parva; sub-parva: Astika Parva).
The devas, the sons of Aditi, and the danvas, the sons of Diti, were fighting over the pot of amrita that Dhanvantari, the heavenly physician, had brought out of the ocean during Samudra Manthana. To prevent the danavas from becoming immortal by drinking the amrita, Vishnu appeared in the form of Mohini, the goddess of seduction. Mohini wooed the danvas, and made them agree to her plan for distributing the amrita. She made the devas and the danavas sit in rows, and began to distribute the amrita—the devas were the first recipients.
Svarbhanu became suspicious. Disguised as a deva, he sat in the row of devas and received amrita from Mohini. The moment the amrita dropped into his mouth, the Sun God and the Moon God recognized Svarbhanu. They alerted Vishnu, who used his Sudarshan Chakra to slice Svarbhanu’s neck before the amrita could drop into his body.
Svarbhanu’s head became Rahu, the implacable enemy of the two Gods—the Sun and the Moon—who were responsible for alerting Vishnu. Rahu took the vow of eating the Sun and the Moon from time to time, and since then he has been the cause of eclipses. The torso of Svarbhanu became a headless demon called Ketu, a directionless comet. Rahu is represented as a cosmic serpent’s head, while Ketu is represented as the serpent’s tail.
Rahu and Ketu are part of the Navagraha (nine planets) system of Hindu astrology which is based on nine cosmic bodies: Surya (sun), Chandra (moon), Mangala (Mars), Budha (Mercury), Brahaspati (Jupiter), Shukra (Venus), Shani (Saturn), Rahu, and Ketu. Identified as the invisible cosmic bodies which reside at the points of intersection in the paths of the sun and the moon, Rahu and Ketu possess the power to influence, mostly unfavorably, the life of human beings.