Thai Amavasai is the first New Moon day after the Sun has started its celestial journey into Northern hemisphere. The Sun represents the soul in Vedic astrology and he helps one seek ancestral blessings to a great level during this time.
Doing tarpanam on Thai Amavasya is significant for the fact that the Sun has entered the house of Saturn (Capricorn) who removes the negative ancestral karma for one. Thus, Thai Amavasai gains immense significance on account of the start of the Uttarayana through the beginning of the northward journey of the Sun who enters Saturn’s house.
Thai welcomes the warmer days of the Spring and Summer and thus revitalises one with energy. Thai Amavasya is significant on this note as one gets lots of energy through the ancestral blessings when one performs homage to his ancestors through oblations like tarpanam.
It is believed that one’s ancestors come down to earth to bless him on this day. Taking a holy dip in the sea or any water body on this day is considered auspicious by devotees. People visit Rameswaram, Sethukarai, Kanyakumari, Devipatinam, Dhanushkodi and Muhuntharayarchathram to pay homage to their ancestors on this day
Mauni Amavasya occurs in Maga month during January and February as per the traditional calendar followed in North India. It is also called Maghi Amavasya and is the last Amavasya before the occurrence of Sivarathri. As the term Maunide notes,
Mauni Amavasya is a day for observing silence and through that silence seeking self-realization and spiritual wisdom. When the mind is silent, it is set upon deep meditation to take a journey into the soul and realize self.
Mauni Amavasya is considered powerful since the sun and the Moon enter the sign of Capricorn on this day.
On the day of Mauni Amavasya, people take a bath in holy rivers like the Ganges. It is considered equivalent to conducting Rajasuya yagna and Aswamethayagna.
And on this day, it is considered sacred to donate clothes to the needy and the poor, offer food to the downtrodden, help the kushta rogi and conduct homams.