All the planets, which I have discussed above, have physical and visual existence. But Rahu and Ketu have no physical shape. These are the imaginary points in the sky. But even then, Rahu is considered most powerful and has been allotted the status of a planet by our Rishis and seers. Mostly, Rahu confers malefic effect. He is considered a dirty planet indicating laziness, filthiness, delays and hurdles. He stays for 18 months in a zodiac sign.n Hindu mythology there is an interesting fiction that describes how Rahu and Ketu came into existence. Once both, the gods and the demons agreed to form an alliance to produce nectar that could give them immortality. Nectar was to be obtained by churning the ocean. In the process, nectar was churned out. When the nectar was being served to the gods, a demon, disguised as a god, and sat between the Sun and the Moon in an attempt to acquire the nectar. The demon was recognized by the Sun and the Moon who complained of the demon to Lord Vishnu. Lord Vishnu immediately severed his head from his chakra. But the demon had already consumed enough nectar to make him immortal. The head of the demon, known as Rahu, became immortal. And the remaining corpse of the demon was known as Ketu. Ever since, Rahu and Ketu became the strong enemy of Sun and Moon. Sun and Moon eclipses occur due to Rahu and Ketu who swallow up Sun and Moon when they come near to them. In this way Rahu and Ketu take their revenge from Sun and Moon.
In Vedic astrology Rahu and Ketu are known as two invisible planets and they are strong enemies of the Sun and the Moon. Rahu and Ketu are actually the astronomical points in the sky respectively called the north and south lunar nodes. The places of intersection where the Moon`s path meet the Sun`s path is known as North Lunar Node and South Lunar Node respectively. Thus, the relation of Rahu and Ketu with Sun and Moon has been described through the language of symbol in Hindu mythology.