Thai Amavasya is a no moon day that occurs during the Tamil Month of Thai (January – February in English months). This is the first Amavasai of Utharayanam i.e. when the Sun moves North. Thai Amavasya is on the Poushya Amavasya day in Marathi, Gujarati, Kannada and Telugu calendars and on the Magh Amavasya day in North Indian Hindi calendars. It is also celebrated as Mauni Amavasya.

On Thai Amavasya, hundreds of people pay homage to their ancestors. It is special for the Thithi and Tharpanam and devotees fast and have only one meal on this day. One has to observe complete silence and pray to Sri Vishnu. With this, one is able to get rid of the shadripus such as kama, krodha, lobha, moha, madha and matsarya.

In Tamil Nadu, Hindus take a holy bath in one of the sacred water bodies. Shradh and Tarpan are offered. On Thai Amavasi day the souls of the dead visit and bless their live relations. The rituals and other pujas are performed on riverbanks or on seashores.

The day is of great significance at the Rameshwaram Ramanatheshwarar Temple . Rituals, pujas and prayers associated with Thai Amavasi are devotedly followed in several places in Tamil Nadu including Kannyakumari, Dhanushkodi, Muhuntharayarchatram, Sethukarai and Devipattinam.