Everyone knows that January 1 is New Year’s Day. But that was not always so—and depending upon your origins or where you live in the world even today it may still not be so. The early Romans held that March 1 was the day when the New Year began. In 46 BC, Julius Caesar introduced a solar-based calendar to correct the inaccuracies in the ancient Roman and earlier lunar calendars and decreed that the New Year would begin on January 1.
In 1582, Pope Gregory XIII reformed the Julian calendar using a solar dating system. By the Julian reckoning, the solar year comprised 365 1/4 days; the intercalation of a “leap day” every four years was intended to maintain correspondence between the calendar and the seasons. A slight inaccuracy in the measurement (the solar year comprising more precisely 365 days, 5 hours, 48 minutes, 46 seconds) caused the calendar dates of the seasons to regress almost one day per century.
This regression had amounted to 14 days by Pope Gregory's time. He based his reform on restoration of the vernal equinox, then falling on March 11, to the March 21. The change was effected by advancing the calendar 10 days after Oct. 4, 1582, the day following being reckoned as October 15. So October 5-14, 1582 are dates that never happened.
January 1 on the Julian calendar currently corresponds to January 14 on the older Gregorian calendar, and it is on that date that followers of some of the Eastern Orthodox churches celebrate the New Year today, mainly in the countries of Belarus, Bulgaria, Cyprus, George, Greece, Macedonia, Moldova, Montenegro, Romania, Russia, Serbia, and Ukraine.
Most countries in Western Europe officially adopted January 1 as New Year's Day shortly after 1582. Scotland moved the first day of the New Year from March to January 1 in 1600 by decree of King James VI. In England, however, the Feast of the Annunciation on March 25 was the first day of the New Year until 1752. Consequently, a child born in Britain before 1752 on, say, January 15, 1623 would have been given what we now consider the previous year as the birth year because this child’s new year wouldn’t begin until the end of the next March. To bring the birth date into conformity with later standards, it is now customary to give the previous year and next year as the date in this form: 15 January 1622/23, indicating that in his own time, this person would have been said to be born in 1622. We would now say that he was born in 1623, but genealogists like to stick to the double year format.
The most recent Jewish New Year, 5772, known as Rosh Hashanah, was at sundown on September 28, 2011. In 2012 it will be September 16, Jewish Year 5773.
Rosh Hashanah occurs 163 days after the first day of Passover. In terms of the Gregorian calendar, the earliest date on which Rosh Hashanah can fall is September 5, and the latest date it can occur is October 5, as happened in 1967 and will happen again in 2043.
In China, the determination of when the New Year begins is based on a lunar calendar. One scheme of figuring out the date (there are several) placed the beginning of the year 4708 as February 3, 2011. It usually falls between 20 January and 20 February.
The Hindu New Year falls at the time and date the Sun enters Aries on the Hindu calendar, normally on 13 or 14 April depending on the Leap Year. And the Islamic New Year moves from year to year because the Islamic calendar is a lunar calendar.
The calendar now in general worldwide use had its origin in the desire for a solar calendar that kept in step with the seasons and possessed fixed rules of intercalation. Because it developed in Western Christendom, it had also to provide a method for dating movable religious feasts, the timing of which had been based on a lunar reckoning. To reconcile the lunar and solar schemes, features of the Roman republican calendar and the much earlier Egyptian calendar were combined.
So, at some point in the coming year, everyone should have a Happy New Year, but maybe not on January 1!