Sashti Viratham is an important vritham of Lord Muruga. Sashti September 2011 date is 3 September, Saturday.
It falls in Avani masam as per Tamil calendar. It is also observed as Surya Shashti in other places of India. It falls in Bhadrapada month as per those Panchangams.
The other Sashti in September 2011 is 18 September, Sunday. It falls in Purattasi Masam in Tamil calendar.