Here is your short paragraph on Chhat festival:
The festival of Chhat in honour of the sun god is observed in large parts of Bihar and eastern Uttar Pradesh.
The rituals of Chhat are usually performed on the bank of a river or a large tank.
Here a large crowd of devotees assemble on the bank of the Ganga at Patna to make an offering to the Sun god.
After a prolonged fast, offerings are made to the setting sun on the six day of the new moon in the month of Kartik, i.e. six days after Diwali.
Women offer arghya to the rising sun on the seventh day of the new moon in Kartik. Chhat festival is popular in Surajpur-Baragaon near Nalanda ruins. It is held twice in the month of Kartik (October-November) and Vaisakh (April-May).