Thiru Kaarthigai or Kaarthigai Deepam, is observed in the month of Kaarthigai (mid-November to mid-December), when the moon is aligned with the constellation of Karthigai and Pournami. It marks the day Lord Murugan was formed from six sparks of fire that emanated from Lord Shiva’s third eye. These sparks were nurtured by six Karthigai maidens and merged to form the six-headed Murugan.
On this day, homes and temples are illuminated with rows of oil lamps (agal vilakku), symbolising the dispelling of darkness and ignorance.