Significance
Karthigai Deepam is the most important festival of Tamil Nadu, falling on the full moon of the Tamil month Karthigai (November-December) when the moon is in the Krittika (Pleiades) nakshatra. It celebrates Lord Shiva's manifestation as an infinite column of fire (Jyotirmaya Linga) -- the Arunachala Deepam, where a giant flame is lit atop the Annamalai hill in Tiruvannamalai and seen for miles. Homes are illuminated with rows of oil lamps (vilakkus), symbolizing the removal of ignorance by the fire of divine knowledge. Every lamp lit is an act of cosmic significance.
Preparation
Rituals & Vidhi
Home Lamp Lighting
At dusk, light lamps in every corner of the home -- in the puja room, at every doorway, on the compound wall, and at the Tulsi plant. The home should be entirely outlined in light.
Shiva Puja
Perform puja to Lord Shiva in the form of Jyotir-linga. Offer Bilva leaves, white flowers, and sesame oil. Meditate on Shiva as the infinite flame.
Mantra: Om Namah Shivaya. Annamalai Arulvai.
Krittika Star Watch
At moonrise, observe the full moon in the Krittika nakshatra (the Pleiades cluster). The sight of the moon in Krittika on this night is considered supremely auspicious.
Prasad Sharing
Distribute Pori Urundai (puffed rice jaggery balls) and kadalai (roasted gram) -- traditional Karthigai sweets -- to family, neighbors, and the poor.
Family Guidance
This is one of the most visually magical festivals for children. Let them light lamps around the house threshold under supervision. Tell the story of Shiva as the infinite pillar of fire that neither Brahma nor Vishnu could find the end of.