Thai Amavasya is the first Amavasya which falls in the sacred Uttarayana period and hence, is held as even more auspicious for performing various rituals dedicated to the ancestors. Non-performance of such austerities is believed to bring us bad luck and can become the cause for Pitru Dosha or ancestral curse. people, therefore, choose this particular occasion for performing ceremonies to propitiate the departed souls and receive their blessings.
The Thithi of the dark moon, when the moon is not seen in the sky, is referred to as Amavasya Thithi or simply as, Amavasya. As per the hindu lunar calendar that is widely used in india, a lunar month starts on Pournami or poornima or the full moon day, and Amavasya falls in the middle. Amavasya is considered auspicious for various activities, especially for worshipping the ancestors.
Thai is the 10th month of the tamil Calendar, which corresponds to mid-January–mid-February and is regarded as a very auspicious one. It begins on the sacred Uttarayana day, when the sun starts on its northward journey in the celestial sphere. It is on the same day that the important festival of pongal is also celebrated.