Chhath is an ancient Hindu festival historically native to the Indian subcontinent, more specifically, the Indian states of Bihar, Uttar Pradesh, Jharkhand, and the southern parts of Nepal. It has become popular with the Nepali hilly community in the recent years, thanks to the influence of the southern immigrants. Prayers during Chhath puja are dedicated to the solar deity, Surya, to show gratitude and thankfulness for bestowing the bounties of life on earth and to request the granting of certain wishes. Chhathi Maiya, the mother goddess and Sun’s sister, is worshipped as the Goddess of the festival. It is celebrated six days after Diwali, on the sixth day of the lunar month of Karthika (October–November) in the Hindu calendar Vikram Samvat. The rituals are observed over four days They include holy bathing, fasting and abstaining from drinking water (vrata), standing in water, and offering prasad (prayer offerings) and arghya to the setting and rising sun. Some devotees also perform a prostration march as they head for the river banks.
Environmentalists have claimed that the festival of Chhath is one of the most eco-friendly religious festivals. All devotees prepare similar prasada (religious food) and offerings. Although the festival is observed most elaborately in the Madhesh (southern) region of Nepal and the Indian states of Bihar, Uttar Pradesh and Jharkhand, it is also prevalent in areas where the diaspora and migrants from those areas have a presence. (snappywap.com) It is celebrated in all northern regions and major north Indian urban centers like Delhi . Hundreds of thousands of people celebrate it in Mumbai
Legend dictates that Chhath Puja has been performed since the Early Vedic Period and sages from this era used to perform the prayers by exposing themselves to direct sunlight to get energy and life force from the rays of the sun, after having maintained a fast. This ritual is still carried out by various people in their own prayers.
This festival is one of the few Hindu celebrations where there is no idolatry involved. It is dedicated solely to the worship of Shashti Mata and the Sun God Surya, along with his consorts Usha and Pratyusha, the Vedic Goddesses of Dawn and Dusk respectively. It is believed that the true source of the Surya are his wives, Usha and Pratyusha.
Chhath is considered as the most environmentally friendly festival as in its essence it is the worship of elements in nature and is often used to spread the message of nature conservation. Even more so, Chhath is one of the very few Hindu festivals that transcends the rigid restrictions of the caste system, which emerged for the post-Vedic period. It touched upon the ideas of equality, fraternity, unity and integrity. Each devotee, regardless of their class or caste, prepares the same offering for the Sun God and arrives at the banks of the rivers and ponds for extending prayers.