Ketu is a mysterious planetary influence, which, like Rahu, is malevolent and afflictive unless located in a powerful position or conjoined with a beneficent planet. Ketu governs theology, monastic life, crime and punishment, hidden enemies and dangers, and the occult. Unless correctly balanced, Ketu can cause poverty and other obstructions in one's life. Ketu is associated with suffering and the consequent aspiration for spiritual liberation.

If Ketu is exalted one will be wealthy and protected from evil. But if Ketu appears in a weak or harmful position in one's horoscope, one becomes prone to fatal diseases of a mysterious nature as well as compulsive gambling.

Gemstones ruled by Ketu include Cat's eye, beryl, tourmaline and other yellow to greenish-brown gems which display a strong chatoyant "cat's eye" light reflection on the surface and often within the crystal when cabochon cut. These gems should also possess a high degree of transparency in order to properly transmit beneficial Ketu energy.