Rarhu is mentioned explicitly in a pair of scriptures from the Samyutta Nakaya of the Pali Canon. In the Candima Sutta and the Suriya Sutta, Rarhu attacks Canda, the moon deity and Suriya, the sun deity, before being compelled to release them by their recitation of a brief stanza conveying their reverence for the Buddha. The Buddha responds by enjoining Rarhu to release them, which Rarhu does rather than have his "head split into seven pieces". The verses recited by the two celestial deities and the Buddha have since been incorporated into Buddhist liturgy as protective verses (paritta) recited by monks as prayers of protection.
In Buddha Rarhu is one of the krodhadevatas (terror-inspiring gods)
Rarhu is the ascending lunar node. In Hindu mythology, Rarhu is a snake that swallows the sun or the moon causing eclipses. He is depicted in art as a dragon with no body riding a chariot drawn by eight black horses.
According to legend, during the Samudra manthan, the asura Rarhu drank some of the divine nectar. But before the nectar could pass his throat, Mohini (the female avatar of Vishnu) cut off his head. The head, however, remained immortal. It is believed that this immortal head occasionally swallows the sun or the moon, causing eclipes. Then, the sun or moon passes through the opening at the neck, ending the eclipse.
There is another lila of Shiva and Rarhu probably taken from Sivapuranam which is paraphrased by Joseph Campbell in his book. The Power of Myth Ganna Chakra also paraphrases the myth:
In the myth of the Daitya king Jalandhara, Jalandhara sends Rarhu with a message to Shiva, demanding that he surrender Parvati to Jalandhara. Shiva was angry at this message, and this anger took the form of a terrible creature which sprang from his brow. It had the face of a lion, flaming eyes, body which was dry and rough to the touch, long arms and a tongue which lolled with anger. The creature rushed at Rarhu, ready to devour him. Shiva apparently said something along the lines of "we don't shoot the messenger" whereon the gana pleaded to Shiva that it was tortured by hunger. Shiva told the gana that if it was so hungry, it should eat its own flesh. This the gana did, until only its head was left. Shiva, pleased with such devotion, appointed the gana as his door keeper, ordering that it create terror for all wicked people. Shiva also ordained that the gana be worshipped along with his worship, and gave it the name Kirtimukha.
In Thai legend, Rarhu appears as the younger brother of two men who are reincarnated as the sun and moon. Unhappy at being overshadowed, Rarhu is constantly striving to dim their brilliance by swalling them; and occasionally he is successful. In Thialand, devotees normally burn black joss sticks and present eight black offerings, including black-feathered chickens and coffee, to appease the dark angel in the run-up to the eclipse.
By Richard Brown
The legend of Rarhu (the eclipse): as it appears in the encyclopedia of Vedic history, the Srimad Bhagavata Maha-puranam: Canto VIII Chapters 5-9 (circa 3,000 BC).
First a brief background of this ancient history. Cast of characters: At the beginning of creation, Lord Vishnu, the eternal Supreme Being, entered his own unmanifested material nature (Prakrity); from his navels was born the first being, Brahma (the four-faced), who is the empowered material creator; from Brahma's third eye, in anger, appeared the great Lord Shiva (destroyer of the cosmos), along with the demigods (devas) and the demon (asuras).
At this time there was a great attempt by the demigods and demons to churn the ocean to milk (primordial soup) to obtain the nectar of immortality. Lord Vishnu incarnated himself as Kurma-avatar (center of the Universe); and the celestial serpent, Vasuki, was to be the churning rope. The demigods, being humble by nature, took hold of the tail of Vasuka, while the demons, who are alway proud, took the fiery head; and thus the churning began.
During the churning provess many wonderful things were produced, until finally the "amrita" or immortal nectar appeared. Immediately there was a fierce struggle and the demons forcefully took possession of the nectar. At that time, to help the demigods, Lord Vishnu, expanded himself into Mohini_murti, the most enchanting of all beautiful goddesses. The demons, who were completely love-struck, allowed the Goddess to have the nectar, which she began to distribute among the demigods.
At that time, the great demon, Rarhu, disguised as a demigod, entered the line of eager devas, between the Sun and Moon gods. As soon as the nectar was tasted by Rarhu, he was exposed by the Sun & Moon gods, and Lord Vishnu, in His Mohini form, immediately severed Rarhu's head with his Sudarshan Chakra (discus). Because Rarhu had tasted the amrita his head became immortal, while his body fell away dead. Seeing this wonderful event, Lord Vishnu, then awarded Rarhu the exalted post of Graha (planetary deity) as the malevolent North Node of the Moon.
Rarhu still hates the Sun and Moon gods for the destruction of his body from the neck down, and he attacked the Sun and Moon out of revenge, following a schedule of eclipses, which are predicted and recorded to this day by astronomers and astrologers.
Astrological Influences: Rarhu is by nature a malevolent planetary influence which can cause personal frustration, sacrileges habits, abuse of alcohol and drugs, possession of ghosts and demons, and infectious diseases. However, when located in a powerful spot in one's horoscope. Rarhu can elevate one to positions of great wealth and power and confer public influence over the masses. Rarhu is associated with serpents, fear, karmic, retribution, and un-virtuous characters.
Person with Rarhu exalted are wealthy and fortunate. But those who have a weak or afflicted Rarhu in their horoscope have a tendency to suffer from fear of supernatural phenomena and suicidal impulses. ULTRA-VIOLET is the cosmic color transmitted by Rarhu through hessonite and other orange gems. Ultra-violet colorwaves are the coldest of all the cosmic rays and should only be used for ailments caused by extreme over heating, i.e., high fever, hyper-acidity, indigestion, hyper-sexualty, insomnia, and during child birth. Rarhu astral talismans may also help divert disasters, prevent insanity, counteract poisons, and protect one from demoniac of lower status, such as servants, employees, and underworld characters.