Rahu Ketu is the name given to the North and South Nodes of the Moon.They symbolically swallow the two luminaries (Sun & Moon) during the eclipses. Their capacity to darken the Sun and the Moon make Rahu Ketu the most powerful influencers. The Sun around whom the other planets and the solar system revolves, the Moon which controls life on earth, are shadowed by Rahu Ketu during eclipses
Rahu is the North Node and Ketu is the South Node. They are points on the eclipse where the Moon is in alignment with the Sun and the Earth. The role of Rahu Ketu in this powerful alignment of the Sun Moon and the Earth gives them the role of the ultimate controllers of destiny. The period after the eclipse is considered the rebirth of the Sun and the Moon. They have been given the status of Planets to emphasize their significance and the importance placed on eclipses. They are known as Chayya Grahas (shadow planets). They have no substance and are physically non-existent. Yet their influence is full of potency and spiritual significance.
Mythology: There are many Myths and legends attached to Rahu Ketu. The most well-known one is of Rahu Ketu as the Naga Vasuki- the ruler of the Patala Loka (the nether regions of the earth). Nagas in Vedic literature are not ordinary snakes but Serpents with much hidden knowledge and wisdom. There was a great war between the gods and the demons for the control of the universe and at the center of it was the ocean which was being churned to find the hidden treasures and the Amrita- the nectar of immortality. Vasuki (the celestial snake) helped the gods in their mission by being the rope tied around the spiritual mountain Mandara, used by the gods to churn the ocean.
When the Amrita was found, the gods wanted to keep it for themselves as they felt that the demons would use it for the wrong purpose. Vasuki being a demon, his instincts were purely for personal glorification and materialistic happiness rather than universal good. Vasuki, was more intelligent than the other demons, he was not willing to be distracted by the gods. He drank the nectar of immortality secretly. The Sun and the Moon complained to Lord Vishnu, the creator of the Universe, who was very angry at this deception. In anger he threw the Sudarshan Chakra at Vasuki and cut him into two. Vasuki had already had the Amrita and was immortal, therefore could not be killed. He remained in the skies as Rahu(the head)Ketu (the lower half), a permanent reminder to the other planets(gods) of the darker side of life which we have to defeat in the pursuit of immortality.
Rahu Ketu are considered great enemies of the Sun and the Moon because they told Lord Vishnu about what Vasuki had done. Rahu and Ketu symbolically swallow the two luminaries during the eclipses. Their capacity to darken the Sun and the Moon make Rahu Ketu the most powerful. The Sun around whom the other planets and the solar system revolves, the Moon which controls life on earth, are obscured by Rahu Ketu during eclipses.