Which calendar begins at midnight on New Year's Eve in the Time ball tradition at Greenwich, England?

The calendar that begins its next year at midnight on New Year's Eve in the Greenwich time-ball tradition is the Gregorian calendar.

The Gregorian calendar is the civil calendar used by most countries today. It was introduced by Pope Gregory XIII in 1582 as a reform of the Julian calendar, mainly to correct the accumulated drift between the calendar date and the seasonal year. Its leap-year rule is more precise because century years are not leap years unless divisible by 400.

A time ball at the Royal Observatory, Greenwich, was first installed in 1833 to provide a visible time signal to ships on the River Thames. The historic time ball still drops daily at 1 p.m., rather than at New Year's midnight. Greenwich is associated with the global time system, but time zones mean local New Year's Eve celebrations begin at different instants worldwide.