On any given day, six puja-s are performed in temples – 
Mornings at 6:00 Ushatkala, 8:00 Kalasandhi and 12:00 Uchikala 
Evenings at 6:00 Sayaraksha, 8:00 Second Kala, and 9.00 Ardhajama.

Similarly, the even the Devas conduct the puja-s at six times a day. But a day for them is a year for us. Uttarayana and Dakshinayana are day and night for them. Special abhishekam is performed on six days a year, corresponding to the daily six puja-s for Lord Nataraja by the Devas. Out of which, three correspond to specific Nakshatra-s and the other three to specific Tithi-s (lunar days).

Thus, the six abhishekam-s to Nataraja for the six-kala puja-s corresponding to the day of the Deva-s are performed as –
Morning Ushatkala during Markazhi (Dhanur), Kalasandhi during Masi (Kumbha) and Uchikalam in the month of Chitra (Mesha) on the day of the Tiruvonam Nakshatra. 
Evening Sayaraksha during Ani (Mithuna), Second Kala during Avani (Simha) and Ardhajama during Puratasi (Kanya). 

The following are the six abhishekam-s performed at Tillai Chidambaram during the year, the abode of Lord Nataraja –

1. In the month of Chitra (Mesha) on the day of the Tiruvona (Shravana) Nakshatra, abhishekam is in the evening at Kanaka Sabha
2. In the month of Ani (Mithuna) on the day of the Uttra (Uttara Phalguni) Nakshatra, abhishekam is at 4 o'clock before sunrise at the Thousand Pillar Hall called Raja Sabha
3. In month of Avani (Simha) on the day of shukla-paksha chaturdashi, abhishekam is in the evening at the Kanaka Sabha
4. In month of Puratassi (Kanya) on the day of shukla-paksha chaturdashi, abhishekam is in the evening at the Kanaka Sabha
5. In the month of Margazhi (Dhanur) on the day of the Tiruvadirai (Ardra) Nakshatra, abhishekam is at 4 o'clock before sunrise at the Thousand Pillar Hall called Raja Sabha
6. In month of Masi (Kumbha) on the day of shukla-paksha chaturdashi, abhishekam is in the evening at the Kanaka Sabha

It is believed that the darshan of Lord Nataraja on these days leads to Moksha or final liberation.