Sashti viratham or Sashti fasting is the most auspicious day to observe Subramanya swamy puja or worship of Lord Muruga. In June 2012, Sashti Viratham date is June 25, Monday. It falls in Aani masam in Tamil calendar.
It is even more auspicious as it falls in Aani month in which Natarajar Abhishekam is celebrated in Chidambaram. This Sashti is also celebrated as Kumara Sashti in other places of India.
The other Sashti tithi in June 2012 is June 10, Sunday. It falls in Vaigasi masam in Tamil calendar.