I have seen my dad doing fasting on every Amavasya in remembrance of my late grandfather i.e., dad's father. He usually will not have breakfast and lunch on that day and directly will have dinner with all variety of food after offering it to a photo of the grandfather and having that food later.
When I asked him why he does so every Amavasya, his reply was "Its on the remembrance of Ancestors" and nothing more than that. I'm not satisfied with his reply.
What is the reason behind doing so every Amavasya? Does it have any significance with Hindu history and Hindu scripts? Is it more than any beliefs? Can anyone help me out with this?