In ancient India, these planets were called shadow planets because they are subtle, non-physical entities—lacking mass or visible form.

According to the Puranas, the demons (asuras) could resurrect the dead using the Mrta-sanjivani mantra, while the gods (devas) could not.

Seeking help, the devas approached Vishnu, who told them that if they churned the Primordial Ocean, they would obtain amrita, the nectar of immortality. But the devas couldn’t accomplish this monumental task alone, so they invited the asuras to help, promising them a share of the nectar.

Using the cosmic serpent Vasuki as a rope wrapped around the sacred mountain Meru, the asuras pulled on one side and the devas on the other, churning the vast ocean. When the amrita finally appeared, a fierce dispute broke out over its distribution. The demons wanted to seize the nectar entirely for themselves and establish their dominance over the universe.

Hearing the devas’ prayers, Vishnu assumed the form of an enchanting woman—Mohini Murti. Captivated by her beauty, the demons willingly handed her the amrita. Mohini cleverly distributed the nectar so that it all went to the gods.

However, one demon, Rahu, didn’t trust Mohini Murti. He secretly disguised himself as a god and slipped into the devas’ ranks, managing to drink some amrita. But Surya (the Sun) and Chandra (the Moon) recognised him and exposed his deception. In response, Vishnu hurled his flaming discus—the Sudarshana Chakra—at Rahu, cutting off his head.

Yet because Rahu had already tasted the nectar of immortality, both his head and body remained alive. From that moment forward, his head became known as Rahu, and his body and tail as Ketu.

Ever since, Rahu and Ketu have been eternal enemies of the Sun and Moon. From time to time, they attempt to “devoir” the luminaries, causing solar and lunar eclipses. But the Sun and Moon always manage to escape because they too are immortal.