These fifteen days start from September 5th in India (and on the 4th in the U.S.), right after the full moon and ends on the Mahalaya New Moon day, September 18th. This two week period is the most important period to appreciate your departed ancestors.
Why should I worry about my departed ancestors?

Spiritually speaking there are two reasons for all of our mundane problems. One caused by the planets, the other by departed spirits. We should constantly take care of them in order to have a peaceful life.
Just as there is biological lineage of transference of DNA along the family line, there is spirit lineage. It is as though there is a spirit DNA as well. Your departed ancestors can help solve your problems.
Our ancestors live in the world of the Pitra loka (ancestral world). 64 Generations of dead ancestors can help solve your money, relationship, health and other problems quite easily if one knows how to communicate and connect with them.
How to access my ancestor’s blessings

On the new moon day, the departed spirits come to the earth plane and stay with their biological relatives from sunrise to sunset. Fasting during the new moon day will alert your consciousness to be in communion with their spirits.
During these 15 days, our Ancestors want special food: a special offering comprised of black sesame seeds, holy water from rivers and oceans, tulsi leaves, sandalwood paste, sacred dharba grass and some coins. These offerings need to be given to them for all the 15 days conscientiously.
Ancestral offerings are acknowledged by all cultures – Egyptian, Chinese, Japanese, Indian, Judeo-Christian, Aboriginal, African, etc. Astroved has become a brand name for Tarpanam rituals. We have specialists who can ensure that offerings do reach the spirits.
Even great Siddhas like Agastiya, Maha Rishis like Vasistha, Avatars like Krishna and Rama, when they lived on the earth plane appreciated their ancestors through rituals called Tarpan (Tarpanam in Sanksrit).
What awaits me during Mahalaya Fortnight?
The sacred "Maha Tarpanam" ritual will be performed in Kerala for each of the 15 days. Our ancestral specialist priests ensure that the ancestral souls are appeased and bless you.
Significance of the 15 day ritual:
The Maha Ancestral ritual spans for 15 days from the 1st Moon till the New Moon and each day is ruled by a specific phase of the Moon.