Why is diwali celebrated? Story of Deepavali (ദീപാവലി കഥകളും വിശ്വാസങ്ങളും)

Skanda Purana says that Deepavali was celebrated from Satyayuga. Even though the celebrations are different and the mythology is said differently in each part of India, the divinity behind the day is the same. According to one's own belief the importance of Deepavali kept changing. This narration explains when the celebration started and why deepavali is celebrated for 5 days.