Aani Uthiram, or Ani Thirumanjanam, is an auspicious day in the Tamil Month of Aani (May -June) and is dedicated to Lord Nataraja (Shiva). The word "Thirumanjanam" means Holy bath. The festival is observed on the Uthiram Nakshatram day. In 2009, the date of Aani uthiram was on June 29. 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.
- Marghazhi-Thai: early winter;
- Masi-Panguni: late winter;
- Chittirai-Vaikasi: early summer;
- Ani-Adi: high summer;
- Avani-Purattasi: autumn;
- Aippasi-Karthikai: rainy season.
It is popularly believed that it was on Aani Uthiram day that Lord Shiva 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.
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Source : http://www.bhattar.com/html/may_june.html