Ketu is the descending lunar node in Vedic, or Hindu astrology. Rahu and Ketu are points in space where there is occurrence of eclipses. They are not physical planets which can reflect light. Rahu and Ketu are also referred to as shadow planets. They are points on the ecliptic where the Moon is in alignment with the Sun and the Earth. They indicate the precise point of the harmony with the three most important influences in our life- the Sun, the Earth and the Moon. This relationship plays an important part in the enfolding of individual consciousness. After the head of Svarbhānu, an Asura (demon), was cut off by the god Vishnu, his head and body joined with a snake to form 'Ketu', representing the body without a head.With an imagery of a headless, half-bodied, smoky planet, Ketu is generally known as the planet of illusion, detachment, spirituality, asceticism, secrets, apart from various other things. Ketu is the planet of otherworldly desire, or spirituality. Ketu represents the spiritual process of evolution, or the refinement of materialization to spirit. Ketu is considered a worldly malefic and spiritual benefice, as it causes sorrow and loss, which ultimately turns the individual to god. They symbolically swallow the two luminaries during the eclipses. Their capacity to darken the Sun and the Moon make Rahu Ketu the most powerful influences in the Zodiac. 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. Rahu Ketu represent Cosmic Law which everyone including the Sun and the Moon have to obey. This allegory has to be understood as life. The Gods without the help of Vasuki (Rahu Ketu) could not find the secret of immortality. In the same way we as humans cannot find our higher selves without understanding the lessons of Rahu and Ketu. They represent the darker side of our nature which we need to overcome.
