पिशाच (piśāca) refers to a class of beings having a yellowish appearance. The yellowish color is derived from the sign Scorpio which has a light-yellow or grey-yellow shade.
Most scholars equate them to be demons like Asura as they prefer the darkness or Rākṣasa as they are violent beings. The word ‘sura’ is for Sūrya and shows the beings who dwell and thrive in sunlight – ‘asura’ is merely a negation of this and shows those who thrive in darkness. This can also be the Moon who is the lord of the dark night. As such human beings are petrified by the darkness of the night and would attribute everything to be evil, which need not be true. Asura are associated with the 8th bhāva which is like a dark deep well. Rākṣasa indicates violent beings who feed on flesh and who bring about the longing for ‘rakṣa’ or protection. In jyotiṣa they are associated with the 6th bhāva of enemies who are always attacking.
They are also said to be fond of flesh as derived from the word पिशित (piśita) meaning flesh which has been cut up or prepared or any flesh or meat. This can also mean having a propensity to cut up the body of other beings like serial killers or psychopaths. They are associated with butcher shops, graveyards and all such places where the animal body is dismembered and cut apart.
The jyotiṣa graha Ketu has the power to awaken the piśāca. Ketu is of agni tattva like the Sun and Mars but represents infra-red light instead of the visible spectrum which symbolises these beings that cannot be seen by the naked eye. They are a personification of the ‘dark fire’ or some very strong infra-red electromagnetic radiation.
They are the children of Krodha (personified anger) and have excessive fondness for quarrelling all the time. This is the power of Ketu like the foot soldiers in the army, who is driven by anger and becomes completely headless in battle. Mars, the army general, never loses his head and is very cool and charming, even the greatest adversity.
There are a total of twenty-seven such evils that have their source in the 27 nakṣatra which manifest the manas (mind) of the person. Eighteen of these (9×2=18) are of higher potency and are called Mahāgraha. These are Amara, Asura, Naga, Yakṣa, Gandharva, Rākṣasa, Heydra, Kasmala, Nistejas, Bhasmaka, Pitṛs, Krisa, Vināyaka, Pralapa, Piśāca, Anthyaja, Yonija and Bhūta while the nine lessor ones are Apasmara, Brāhmaṇa, Brahma Rākṣasa, Kṣatriya, Vaiśya, Śūdra, Nīca, Caṇḍāla and Vyanthara.
All these evils have their origin from the anger of Rudra – that is the seed for their creation. In jyotiṣa, the prāṇi and aprāṇi rudra are the lords of the 2nd and 8th bhāva. There are various combinations to know the source of these evils that cause such terrible suffering, afflictions and in the case of the Mahāgraha, even death.