Chhath festival is celebrated by natives of Mithila Region of Nepal. This festival is dedicated to god Sun. Sun is called Surya in Sanskrit, Chhat festival is thanks giving to lord Surya for sustaining life on earth and to worship him to provide his continuous blessings to mankind.
Hindu people believe sun helps to cure many illness and diseases. Sun is considered as source of healing too. Sun is also considered as token of stability and prosperity.
this photo taken from Kathmandu Kamalpokhari .