Monthly Tamil observance on Karthigai nakshatra day — lamps are lit in honor of Lord Murugan and Shiva.

Masik Karthigai is observed each month when the Krittika nakshatra prevails, and is dedicated to Lord Murugan and to Shiva as the pillar of infinite light. The six stars of Krittika are the six celestial mothers who nursed the infant Murugan, and the six sparks of Shiva third eye that became him. The observance is centred on lamps: rows of oil lamps are lit at dusk in homes and temples, marking the day Shiva appeared before Brahma and Vishnu as an endless column of fire. In Tamil Nadu this monthly Karthigai is kept faithfully as a smaller echo of the great Karthigai Deepam in the month of Karthigai, and is especially observed by devotees of Murugan seeking clarity, courage and protection for their children.

Full fasting is not required. Many keep a satvik diet through the day and take a meal after the evening lamps are lit. Devotees of Murugan may keep a partial fast until dusk.