The Times Square Ball in NYC is dropped during what celebration?

Revelers began celebrating New Year's Eve in Times Square as early as 1904, but it was in 1907 that the New Year's Eve Ball made its maiden descent from the flagpole atop One Times Square. Seven versions of the Ball have been designed to signal the New Year. The first New Year's Eve Ball, made of iron and wood and adorned with one hundred 25-watt light bulbs, was 5 feet in diameter and weighed 700 pounds. It was built by a young immigrant metalworker named Jacob Starr, and for most of the twentieth century the company he founded, sign maker Artkraft Strauss, was responsible for lowering the Ball.

Source: Times Square NYC