KATHMANDU, NEPAL, November 18, 2013 (Kathmandu Post): The Chhath festival is observed with great care and purity. Chhath celebrations revolve around offering homage to the Sun. The festival spans four days, starting from the fourth day of the waxing moon to the seventh day in the month of Kartik, as per the lunar calendar. Throughout this festival, all activities are accompanied by specific songs—whether it’s the preparation of worship materials or visits to ponds and rivers for Sun-God worship. These songs convey messages of fraternity, love, nonviolence, humanity and companionship. The Chhath Festival, predominantly celebrated by Hindus in Nepal’s southern plains, is now observed throughout the country. The festival involves offerings made during both sunrise and sunset.

Mithila has a rich cultural heritage dating back to ancient times. Its vibrant culture is also distinctly unique. Throughout the year, Maithili life pulses with the anticipation of numerous festivals, demanding thorough preparation. The locals eagerly look forward to these festivities, with Chhath being one of the grandest celebrations. The Sun holds a revered place in all civilizations as a visible Deity. While the rising sun is worshiped universally, Maithili individuals also worship the setting sun. On the day of Chhath, devotees enter the water to offer prayers to the setting sun. They spend the entire night on the banks of ponds or rivers and offer prayers to the rising sun the next morning. Alongside the sun, they worship Chhath Parameshwari (Goddess), seeking Her blessings for a healthy and happy life. The Goddess is believed to protect against leprosy and skin diseases, bless infertile couples with children and ensure overall well-being, fraternity, prosperity, social goodwill, happiness and peace for Her devotees and the community as a whole.

More on the festival at source.
https://kathmandupost.com/art-culture/2023/11/18/sun-songs-and-chhath-celebrations