Aani Uthiram, or Ani Thirumanjanam, is an auspicious day in the Tamil Month of Aani (May -June) and is dedicated to Lord Nataraja (Siva). The word "Thirumanjanam" means Holy bath. The festival is observed on the Uthiram Nakshatram day. It is believed that Lord Nataraja gives darshan in the months Ani and Margazhi. The Lord’s form demonstrates his five-fold functions: creation, preservation, destruction, concealment and salvation. :

  • The rattle (udukkai) in his right hand represents creation;
  • his raised right arm with the open palm (abhaya hastam) protection;
  • his left hand holding fire destruction;
  • his firmly placed foot concealment;
  • and his other, slightly lifted, leg salvation.

Lord Nataraja is given six abhishekams in a year. The explanation for that number is as follows. Earth takes 365 days to complete one full circle around the sun. That duration is divided into six seasons :– 

  • Marghazhi-Thai: early winter;
  • Masi-Panguni: late winter;
  • Chittirai-Vaikasi: early summer;
  • Ani-Adi: high summer;
  • Avani-Purattasi: autumn;
  • Aippasi-Karthikai: rainy season.

This six-season year of humans is said to be but one day for the immortals. A day has six periods: dawn, morning, noon, afternoon, evening, and night. These are when the six daily pujas in temples are performed. During each of these six parts, an abhishekam has been ordained for Lord Nataraja. One of these is Ani Thirumanjanam, the pradosha abhishekam on the evening of the day of Uthiram star in the month Ani (June-July). This is the best time for worshipping Lord Siva. 
It is popularly believed that it was on Aani Uthiram day that Lord Siva appeared before Sage Manikkavachakar under a Kurundai Tree and offered upadesha (advice) and during the abhishekam to the Lord, as everyone watched, the sage merged in the Lord as a brilliant flame. Sage Manikkavachakar is the author of Thiruvachakam. 
The Abhishekam or holy bath of the idol performed during the twilight period (Pradosham) on the day is considered highly auspicious. Special rituals and processions are held on the day at Nataraja Temple