Ketu (mythology)

Ketu (Sanskrit: केतु, IAST: Ketú) () is the descending (i.e. 'south') lunar node in Vedic, or Hindu astrology. Personified as a deity, Rāhu (, the ascending (i.e. 'north') lunar node) and Ketu are considered to be the two halves of the immortal asura (demon) Svarbhanu, who was beheaded by the God Vishnu.

As per Vedic astrology, Rāhu and Ketu have an orbital cycle of 18.6 years and are always 180 degrees from each other orbitally (as well as in the birth charts). This coincides with the precessional orbit of moon or the 18.6-year rotational cycle of the lunar ascending and descending nodes on the earth's ecliptic plane. Ketu rules the Virgo zodiac sign together with Budha (traditional ruling planet; Mercury in Western astrology).

Astronomically, Rāhu and Ketu denote the points of intersection of the paths of Surya (the Sun) and Chandra (the Moon) as they move on the celestial sphere, and do not correspond to a physical planet. Rāhu and Ketu are respectively names of the north and the south lunar nodes. Eclipses occur when the Sun and the Moon are at one of these points, giving rise to the story that the these are being swallowed by the Rāhu/ Ketu. Ketu is believed to be responsible for causing the lunar eclipse.