This festival is celebrated in the month of Karthikai (October November) when the moon is in conjunction with the asterism Kritikai (Pleiades). It is believed that Lord Shiva appeared in the form of a pillar of fire to teach the God of Creation (Brahma) and God of Preservation (Vishnu) the knowledge of infinity on this occasion. The "Dhwajasthamba" in temples is said to symbolise this pillar of fire. On this day, to propitiate Lord Shiva, all the houses and temples are lighted and illuminated after sunset. In the temple, there is a custom of burning old items, dry leaves etc called "chokkapanai" symbolising Lord Shiva burning the chariots of Asuras who were troubling the sages. "Chokkapanai" is referred as the chariots of Asuras. On this day, a sweetened fried rice is offered as Naivedyam. The belief goes that King Bali offered this to Lord Shiva to be free from the burning sensation he felt in every part of his bodily tissues. Offering is intended to convey the condition of the cells in the body and seeking Gods mercy. Bali, perhaps, felt that taking fried rice would not build cells causing burning sensation as they were already fried. Thus offering of fried rice (Pori) to Lord Shiva would have arisen. It is also believed that Goddess Parvathi had also observed Karthikai Vratam and offered this to Lord to ward off her sin, the breaking of a Sivalingam unknowingly when she was in fight with Mahishasura.
In South India, at Tiruvannamalai, this festival is observed with great eclat. The presiding deity Arunachaleswarar is one of the five Lingams brought from Kailasa by Sri Adi Sankaracharya. In this temple,in India, is worshipped one of the five elements, AGNI (Fire). Offering of ghee for lamps or lighting lamps with Ilupam oil during Thirukarthikai festival is considered sacred.