Sashti Viratham is observed on the sixth day during the Shukla Paksha or bright phase of moon as per a traditional Hindu calendar. Sashti Viratham September 2011 date is September 3. It is a monthly fasting dedicated to Hindu god Muruga (known as Kartik in North and western parts of India). Special pujas and rituals are also held on the day in Muruga Temples.
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There are two Sashti fasting dates in a month one each during the waxing phase of moon and another during the waning phase of moon. Most devotees fast during the Sashti falling during waxing phase of moon.