The story
Dīpāvali means 'a row of lamps'. In the north the lamps are for Rāma: the people of Ayodhyā lit the road home for him, Sītā and Lakṣmaṇa on their return from fourteen years in exile and the defeat of Rāvaṇa. In the south the day before belongs to Kṛṣṇa's victory over Narakāsura, and in the west it is the day Lakṣmī, goddess of wealth, walks the earth and enters the houses that are lit and clean.
Jains keep the same night for Mahāvīra's liberation, Sikhs for Guru Hargobind's release from prison (Bandī Chhoṛ Divas), and in Bengal the night is Kālī Pūjā. One dark night, many reasons for the light.
The astronomy is the plainest explanation of all: it is the darkest new moon of the year, after the monsoon has cleared the sky, and every house answers it with fire.
