Today, 15 October 2012 is Sarva Pithru Amavasya, Mahalaya Amavasya, Somvati Amavasya. It marks the end of Pitru Paksha Mahalaya, the fortnight dedicated to dead ancestors.
This Mahalaya Amavasya is even more auspicious as it falls on Monday (Somvati Amavasya). Amasomvar Vrat is performed on this day. Punya snan, Ashwattha Pujan (worship of peepal tree), Surya Arghya, Surya Namaskar, Pitru Tharpan, Pinda daan and other rituals dedicated to pitru devatas are considered highly meritorious.
Mahalaya Durga Puja marks the beginning of serious preparations for Durga Puja in Bengal. But actually, it begins on Maha Sashti day.
Mahalaya Amavasya brings the end of Bhadrapada Month in Marathi, Telugu, Kannada & Gujarat calendars. It is Ashwin Amavasya as per North Indian Hindi calendars.
In 2012, this No Moon is Purattasi Amavasai in Tamil calendar and Kanni Month Amavasya in Malayalam calendar.