New Year in different regions is celebrated as per their regional calendar. Countries have their fixed calendar dates and begin their New Year celebrations according to that only. The most popularly used calendars of recent years are Lunar, Solar, Lunisolar and Arbitrary calendars. Today, most of the religions follow either solar, lunar or lunisolar calendar. Arbitrary calendar was only used by the astronomers for references, computations and conversions. Otherwise it does not have any astronomical base
A calendar is a complete system for naming periods of time particularly days. These names are calendar dates. It can be defined as any of various systems of reckoning time, especially with reference to the beginning, length, and divisions of the year. The dates are based on the movement of astronomical objects. Calendar is a register with the days of each month and week in a year. As a subset, it is used to denote a list of particular set of planned events. For example: Court Calendar
Lunar Calendar: It is one which indicates the moon phase. Islamic Calendar is an example of Lunar Calendar.
Solar Calendar: It indicates the revolution of Earth around the Sun to measure time. Persian Calendar is an example of Solar Calendar.
Lunisolar Calendar: It is synchronized both to the motions of the Moon and to the apparent motion of the Sun. An example is the Jewish Calendar.
Arbitrary Calendar: It is not synchronized to either the Moon or the Sun. Its examples are the week and the Julian day.