The fireworks you heard tonight are part of the celebration of Deepavali Melaby (Deepavali Mela / Diwali Festival 2012) by the Association of Indians in America, Inc. The holiday is also known as Diwali, or the "Festival of Lights."
They're being shot off at Pier 16, South Street Seaport in Manhattan.
According to Wikipedia, Diwali commemorates the return of Lord Rama, along with Sita and Lakshmana, from his 14-year-long exile and vanquishing the demon-king Ravana. In joyous celebration of the return of their king, the people of Ayodhya, the Capital of Rama, illuminated the kingdom with earthen lamps and by bursting firecrackers. During Diwali, all the celebrants wear new clothes and share sweets and snacks with family members and friends.
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