Mahalaya is celebrated at the beginning of the Durga Pooja festival, which is observed in the states of West Bengal, Assam, Karnataka, Odisha, and Tripura.
According to Hindu mythology, on this day Goddess Durga defeated the Demon King Mahishasura. It is the last day of Pitu Paksha aka Sarva Pitru Amavasya. Therefore, Mahalaya is the day that marked the arrival of Goddess Durga on the earth with her ultimate power. The day is celebrated with the beautifully designed status of Goddess Durga and various rituals are performed like offering a tarpan, remembering the ancestors, and establishing the idol of Durga Maa in houses and pandals.
As per the Hindu beliefs, In Mahalaya Goddess Durga visits her paternal house. It is believed that Brahma, Vishnu, and Maheshwara created Maa Durga to eliminate the powerful demon whom devatas and human beings were unable to kill Mahisasura.
The Devaloka was ruled by Mahisasura and to protect themselves, the devtas and Lord Vishnu worshipped Adi Shakti to diminish the Asura.
The Fight between the Goddess Durga and Asura took place for around 9 days. On the 10th day, Goddess Durga killed the demon, and with this started the beginning of Navratri and Durga Puja. Varied states have different ways of commemorating this. The earliest ancestors bid farewell to Goddess Durga before she sets off to earth on Mahalaya Amavasya morning.
The day is significant as it is the end of the Pitru Paksha Shraddha and the beginning of Durga Puja for the Bengali community and some parts of India.
Pitru paksha marks the period to worship the ancestors and offer them prayers. On Mahalaya, the devotees pay homage to their forefathers through tarpan or shraddha. From this day, Goddess Durga started her journey from Kailash to the Earth. Durga Puja begins on the seventh day of Mahalaya and it ends on the tenth day of Dusshera.
However, this year Mahalaya is on 6th October 2021. People wake up early morning to worship Goddess Durga by reciting the Chandipath and other devotional mantras.