Kartik Poornima (Kartik purnima) is a Hindu holy day celebrated on the full moon day or the fifteenth lunar day of Kartik (November–December). It is also known as Tripuri poornima and Tripurari Poornima. It is sometimes called Deva-Diwali or Deva-Deppawali – the festival of lights of the gods. The Kartik Purnima festival also coincides with the Sikh festival of Guru Nanak Jayanti.
Tripuri poornima or Tripurari Poornima derives its name from Tripurari – the foe of the demon Tripurasura. Tripurari is an epithet of god Shiva. Shiva in his form as Tripurantaka (“Killer of Tripurasura”) killed the demon on this day. Tripurasura had conquered the whole world and defeated the gods. He also craeted three cities in space, together called “Tripura”. The killing of the demon and destruction of his cities with a single arrow – by Shiva overjoyed the gods and they pronounced the day as a festival of illuminations. This day is also called “Dev-Diwali” – the Diwali of the gods. Diwali is the Hindu festival of lights.
Kartik poornima is also the birthday of Matsya, god Vishnu’s fish-incarnation (avatar). It is also the birthday of Vrinda, the personification of the Tulsi plant and of Kartikeya, the god of war and son of Shiva. This day also is considered dear to Radha, the lover of Krishna – Vishnu’s incarnation. It is believed that Krishna and Radha danced rasa and Krishna worshipped Radha on this day. This day is also dedicated to the pitrs, dead ancestors.
Underhill believes that the origins of this festival may lay in ancient times, when a sacrifice called Shakamedhah was performed to attain victory over enemies.