Ashada Amavasya or the 'No Moon Day' is a very auspicious day in the month of Ashadha.Deepa Puja is the major rite to perform on Ashada Amavasya day.On this day, people clean and decorate their houses and clean all diyas (deepas) they have in their houses and decorate them with colours.
They clean and sanctify a 'Chourang' ie a table with decoration and rangoli (kolam) designs around it. All the deepas are placed on the table and lit to perform pooja.
Deepa Puja is dedicated to the deity of one's choice ie Ishta Devata and to Pancha Maha Bhootas (five primordial elements - Air, Water, Fire, Sky and the Earth).In some cases, devotees dedicate Deepa Puja to the Goddess Lakshmi, Goddess Parvati or Goddess Saraswati.
On this day,all the diyas are lit once again in the evening and placed around the house just like Diwali Puja.It is beleived that the radiations of the light of the diyas drive out all the evil and bad powers and welcome new brightness into their life.
It is also beleived that Deepa Puja provides them Asta Aishwarayas (8 types of wealth). The next day of Deepa Puja (Ashada Amavasya) is the holy Shravan Month.
Gatari Amavasya is a very popular ritual and a festival celebrated in Maharashtra.Gatari Amavas falls on the Ashadh Amavasya day.Gatari is a celebration of joy and happiness.Ashadh Amavas is the last day of Ashad month and the begining of the holy Shravan month.
Maharashtrians abstain from different types of non-vegeterian food in Shravan month,since,the monsoon is at its peak and in this period the stomach is most susceptible to different problems of digestion.So people don't consume hard liquor and non-vegetarian food in full Shravan month.Some of them neither cut the hair nor shave the beard.
Hence the Maharashtrians enjoy this amavasya day by consuming alcoholic drinks to increase the appetite and eating lot of non-vegetarian food.
Gatari Amavasya is also observed as 'Bheemana Amavasya' in Karnataka and 'Chukkala Amavasya' in Andhra Pradesh and 'Hariyali Amavas' in Gujarat state.
Ashada Amavasya is highly auspicious day for Pithru tharpan and Pinda Pradhan.Though every Amavasya day is important to pay our respect to our ancestors, Ashada Amavasya has every kind of significance for Pitru Tharpanam and Pinda Pradhan.
On this day, Pitru devatas are highly active and the every good deed like charity, puja or any other auspicious ritual performed by us will definitely reaches them and provides peace to their souls.