Karthigai Deepam
One of the earliest references to the festival is found in the Ahananuru, a book of poems, which dates back to the Sangam Age (200 B.C. to 300 A.D.). The Ahananuru clearly states that Karthigai is celebrated on the full moon day (pournami) of the month of Karthigai, as per South Indian calendar. It was one of the most important festivals (peruvizha) of the ancient Tamil. Avaiyyar, the renowned poetess of those times, refers to the festival in her songs. Karthikai Deepam is also one of the oldest festivals celebrated by Tamil people till date.
Religious aspects
Lord Shiva appeared as an endless flame of light before Lord Vishnu and Lord Brahma, who each considered himself supreme and said that the matter could be tested if the two could search for Lord Shiva's Head and feet. Lord Vishnu took the form of a boar(Sanskrit:Varaha, Tamil:Varahan) and delved deep into the earth, Lord Brahma that of a swan(Sanskrit:Hamsa, Tamil:Annam) and flew towards the skies. Lord Vishnu failed in his search and returned. But Lord Brahma, chancing upon a piece of Thazhambu, a flower, learnt from it that it had been floating down for thirty thousand years from Lord Shiva's head. He seized upon this and claimed to Lord Shiva that he had seen the other's top. Lord Siva realized the falsehood and pronounced that there would never be a temple for Lord Brahma in this world. He also interdicted the use of the flower Thazhambu in his worship. Lord Shiva appeared as a flame, this day is called Mahapali Deepam.
At Sri Bhavaneeshwarar Temple,
The Mahadeepam is lit by the Hereditary Trustee and placed on the Raja Gopuram. Following which rows of Agal vilakkus (oil lit lamps) are lit all around the temple by the devotees. Karthigai is essentially a festival of lamps. The lighted lamp is considered an auspicious symbol. It is believed to ward off evil forces and usher in prosperity and joy.
After the Deepa Aaradhanai of the Swami and Ambal the Toda Tribes bring the Decorated Palanquin out to witness the lighting of the Chookabhanai following which they are taken on a procession around the temple.
The prasadam distribution draws the screen to the celebrations.
Celebrations at Tiruvannamalai
Karthigai festival in Tiruvannamalai hills is very famous. On Karthigai day, a huge fire lamp is lit up on the hill, visible for several kilometers around the hill. The fire (dheepam) is called Mahadeepam, as Hindu devotees visit the place, to pray and offer lord Shiva.