Many of you know that right now we are in pitru paksh - shraddha. We do this ritual for तृप्ति - Satisfaction - of our departed ancestors. Many priest do full fledged puja for this ritual at the same many people just offer pudding. It is a time for us to fulfill our duties towards our pitru - ancestor.

So I am interested to know what is the reason behind observing pitru paks during THIS TIME only. THIS TIME is defined as Bhadrapad Shukla Purnima ( Fullmoon) to Bhadrapad Shukla Amavsya ( New Moon day ).
Is this time is related to any of नक्षत्र - asterism or there is any other reason. Why do we do this ritual on this specific time only.