Why isn't Diwali celebrated on the same date each year?
The Hindu calendar is based on the lunar cycle and the movement of the moon, unlike the conventional Western (or Gregorian) calendar. The result is that Hindu festivals move about the Western calendar from year to year.
Diwali, for example, falls on the date of the new moon between the Hindu months of Asvina and Kartika. Usually this is in October or November.
What is the story of King Rama and the demon Ravana?
Ravana was the wicked king of the island of Sri Lanka. He was so evil he is shown as having ten arms and ten heads. Ravana kidnapped the wife of Rama.
After a great battle Rama killed the demon and recovered his wife. Rama's return with his wife Sita to Ayodhya and his subsequent coronation as king is celebrated at Diwali.
When Rama and Sita first returned to Ayodhya it was a dark moonless night and they couldn't see where they were going. Their people put little lamps outside their houses so that the new king and queen could find their way, thus beginning the tradition of the festival of lights.