The Chhath Puja is performed in order to thank Surya for sustaining life on earth and to request the granting of certain wishes.
The rituals of the festival are rigorous and are observed over a period of four days. They include holy bathing, fasting and abstaining from drinking water (Vratta), standing in water for long periods of time, and offering prashad (prayer offerings) and aragh to the setting and rising sun.
It is believed that the Maga Purohits (modern days known as Shakya Dwipi Brahmins) were invited by local kings for their expertise in Sun worshiping. They started the tradition of Chhat Puja. Today Chhat Puja is celebrated specially in those places where Shakya Dwipi Brahmins are found.
It is believed that the ritual of Chhath puja may even predate the ancient Vedas texts, as the Rigveda contains hymns worshiping the Sun god and describes similar rituals.