Ketu is the descending lunar node in Vedic, or Hindu astrology. Personified as a deity, Rahu and Ketu are considered to be the two halves of the immortal asura (demon) Svarbhanu, who was beheaded by the god Vishnu.

A lunar node is either of the two orbital nodes of the Moon, that is, the two points at which the orbit of the Moon intersects the ecliptic. The ascending node is where the Moon moves into the northern ecliptic hemisphere, while the descending node is where the Moon enters the southern ecliptic hemisphere.