Amavasya

Since Kanchipuram Mutt where the Adi Shankara lived and all the Pancha-Gauda and Pancha-Dravida use to visit hence Tamil Nadu developed a mixture of Panchangam and saka calendar.

[4] In old Indian culture and beliefs, irrespective of religions, Amavasya is considered a time of great power.

It is believed that a fast on this particular Amavasya would ward off widow-hood in women and ensure bearing of progeny.

Religious people are not supposed to travel or work, and instead concentrate on the rites of Amavasyas, typically at home in the afternoon.

In modern times, a short 20-minute version of the ceremony is done—offering black sesame and water as oblation to departed souls.

These oblations are believed to give birth to good children without mental or physical challenges.

The Kush Amavasya of Bhadrapada month is marked as the auspicious day for uprooting the sacred grass Kusha from farm fields used in Karmakanda, Shraadha, Pitripaksha and some other religious rituals, etc, throughout the year.

[8] The dark fortnight of Aswayuja (September–October) is known as the Pitru Paksha (Mahalaya), which is especially sacred for offering oblations to departed ancestors.

Due to the grace of the Yama, it has been ordained that offerings made during this period benefit all the departed souls, whether they are connected to you or not.