Râhu can be seen as the earliest Vedic astrological pre-science embedded in a story—the ascending and descending nodes created as the moon’s orbit intersects the ecliptic plane of the earth, used in predicting solar and lunar eclipses.
Mythologically, Râhu was one of the great demons (daityas) at the Churning of the Milky Ocean. Râhu managed to change his shape and drink from the pot of immortality-giving nectar (amrita). The sun (Sûrya) and moon (Candra) discovered what he had done and informed Vishnu, who immediately cut off his head.
The upper part, the ascending node, was Râhu, while the lower part of his body was Ketu, the descending node, the dragon’s tail. Râhu would forever attack the sun and moon as they came near, swallowing each of them—only to have them fall out of his severed neck.
Some versions gave him a chariot with eight black horses, racing back and forth across the heavens to attack each of his old enemies. The Purânas stated that Râhu was the son of Kas´yâpa (a progenitor) by his wife Simhikâ, therefore, a daitya. Râhu was worshipped as one of the nine planets (navagraha) in temples.