Why do devotees observe a 36-hour strict fast during Chhath Puja?

Devotees observe a rigorous 36-hour Nirjala Vrat during Chhath Puja, abstaining from food and water as an expression of devotion to Chhathi Maiya and the Sun God. The fast begins after the Kharna ritual on the second day and ends with the morning Arghya on the fourth day. Devotees seek blessings for family well-being, prosperity, and children's longevity.