Modern Facts of the Nine Planets
Rahu (Nodal Planet--North)
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Rahu (North node or Dragon's head) and Ketu (South node or Dragon's tail) are nodes of the Moon. They represent the point at which the Moon's orbit crosses the Ecleptic, As these are the places at which Moon crosses Sun's orbit, eclipses can occur.
Mythologically, the nodes were regarded as the demon which swallows the luminous objects and causes the eclipse. Rahu (ascending node) is at me point at which Moon crosses the Ecleptic in the North and Ketu (descending node) is where the crossing occurs in the south.Rahu's appearance somewhat instills fear in the beholder. While his face looks like that of a deva, the body has scales of a snake.
His flag and seat have a lion, which is his insignia. On his right is his Adidevata cow, and on left is the Pratidevata, a multi-headed serpent.
Elixir of Life
In Hindu mythology, Rahu was the son of the demon, Virprasiddhi, and Simhigai. The search for the elixir of life that guarantees freedom from death appears to have been eternal. In a rare move of cooperation, the devas and the asuras decided to join forces. It was believed that if the ocean called Thiruparkadal--an ocean of milk-was churned, this elixir would appear.
When the elixir appeared, the usual laws of human behaviour came to the fore and both the demons and gods rushed to consume it. Vishnu then appeared as Mohini and persuaded the demons to sit in a row. As they were busy in that process 1fohlOi managed to distribute the elixir to the gods.
Rahu changed his appearance to resemble a dew and got in between Sun and Moon. He started partaking of the elixir and they pointed this out to Mohini (that he was an asura).
Mohini cut off Rahu's head with her ladle. But, as Rahu had partaken of the elixir, he continued to live.
Naturally he turned hostile to Sun and Moon and proceeded to diminish their powers through eclipses. Rahu's head looks like a human. The Asuras banished him and Brahma said he was incapable of reversing the situation as Vishnu had inflicted this punishment!
However, he granted a boon to Rahu and Ketu: Both would become Navagrahas and continue to diminish the powers of Sun and Moon through eclipses periodically. They are also given one and a half hours each day at different times without zodiacal signs. Any venture started during Rahu's time (Rahu kalam) will go wrong; those started during Kethu's time (Kuligai kalam) "will be auspicious!