Chhath Puja dedicated to Lord Surya (the sun god) is a 4-day puja which begins on the fourth day after Diwali in the month of Kartik (October – November) in Sak Samvat calendar. Millions of Hindus who live along
Ganga River and Kosi River mainly (chiefly Bihar and eastern Uttar Pradesh) or trace their roots to the region observe Chhath. Worship of Surya – the Sun God – goes back to the Vedic age, where he is the creator and nourisher. Hymns dedicated to Surya are scattered across the Vedas and the most popular being the Gayatri Mantra.
The origin of Chhath Puja is lost in the obscure misty millennia of ages past. Perhaps the worship might have begun the day man realized the value of Sun (Surya) and how his survival is dependent on this massive fireball that appears without fail each morning and disappears in the evening.
There is a popular belief that Chhath worship was started by the great warrior Karna of the Mahabharata. Karna is the son of Lord Surya and Kunti.
Chhath Vrata and Puja find mention in the Mahabharata. It is believed that Draupadi, the wife of the Pandavas, had performed the Chhath Puja. She performed it during the exile period.