A few billion people will not celebrate the new year next week. Based on other calendars, their calculations show that new year is weeks and even months away.
The Chinese new year will begin in early February. A month later, Muslims will celebrate the Islamic new year. Jews celebrate the new year as Rosh Hashanah, in September.
People in Ireland did not always celebrate New Year's Day on January 1st. The year started on March 25th, the feast of the Annunciation and Lady Day, until 1752, when the Gregorian calendar was introduced.
This system, which updated the calendar developed by Julius Caesar, continues to serve as the international standard for civil use, and regulates religious ceremonies in the Catholic and Protestant churches.
The different dates on which new year falls around the world illustrate many themes in the history of calendar-making, an occupation perhaps best thought of as stemming from a desire to organise units of time to satisfy the needs and preoccupations of society. Calendars were used to map agricultural cycles, for example. More importantly, they were used for controlling cycles of religious and civil events.
Some estimate that 40 calendars are in use, most of them restricted to particular regions or cultures. Across all cultures, one essential characteristic of calendars emerges. Regardless of their level of scientific sophistication, calendars are human constructs, usually bearing the mark of their religious origins.
Some calendars are regulated by astronomical observations, some carefully and redundantly enumerate every unit and some contain ambiguities and discontinuities. Some are codified in written laws; others are transmitted by oral tradition.
The main astronomical cycles are the day, based on the rotation of earth on its axis; the month, based on the moon's revolution around earth; and the year, based on earth's revolution around the sun.
Calendar complexity arises because these cycles of revolution do not comprise a whole number of days. Also, astronomical cycles are neither constant nor perfectly commensurable with each other.
Three distinct types of calendars have resulted from this situation. A solar calendar, of which the Gregorian calendar is an example, is designed to keep in synchronisation with the tropical year, which corresponds to the cycle of the seasons. Then there is the lunar calendar, such as that of Islam, which follows the phases of the moon without regard for the tropical year. Lastly, there is the lunisolar calendar, such as the Hebrew and Chinese calendars, whose sequence of months is based on the lunar-phase cycle, but with an extra month added every few years to bring the calendar back in phase with the tropical year.
The original purpose of the Gregorian calendar was ecclesiastical, to calculate the date of Easter. But it also had to correct several defects of the Julian calendar developed by Caesar, one of which meant Easter fell on inappropriate days.
For four centuries scholars debated the correct time for celebrating Easter - and how to regulate this time through a calendar. In the 16th century, Pope Gregory XIII established a commission to reform the calendar; in 1582, he signed a bull instituting its recommendations.
Christopher Clavius, a Jesuit, wrote the final explanation of the calendar, so an ordinary parish priest could calculate Easter. In his book Mapping Time: The Calendar And Its History, E. G. Richards says Clavius did not have modern measurements of the conjunction of celestial bodies or of the tropical year. Nor did he have the benefit of observations made with a telescope, "even though astronomical knowledge was approaching the point of explosive growth that began in the 17th century". Copernicus laid the groundwork for this revolution. Tycho Brache was still collecting astronomical data. (Kepler was nine. Galileo was a young man.)
The new calendar was spread through the Roman Catholic world. Protestant states initially rejected the calendar, but they gradually accepted it over the following centuries. The civil rules of the Gregorian calendar were slowly adopted around the world, carried by the British empire. It is now all but universally used.
But the calendar will not last forever. The length of the year is slowly decreasing, by about half a second a century. So our calendar will be a day slow by the year 4000.
