|Image from: nightskyinfocus.com|
Once upon a time, in India, the devas (gods) waged war with the asuras (demons). The asura Rahu disguised himself as a deva and stole a bottle of amrita, the nectar of immortality. The sun and the moon witnessed the crime, and they alerted Vishnu.
Vishnu found Rahu and cut off his head, but not before Rahu had taken a mouthful of the amrita. Since the nectar touched his head and throat, Rahu’s head lived.
Rahu appealed to Brahma, arguing that the sun and moon caused him to live forever in a horrible state. Brahman agreed, and he decreed that if Rahu ever catches the sun or the moon, he can eat them as punishment.
Ever since, Rahu chases the sun and the moon across the sky. Occasionally he catches and eats one of them, causing an eclipse. Since Rahu is only a head, the sun and the moon fall out of his throat as soon as he swallows.