Calendar systems and calendar formats vary from region to region. Although the Gregorian calendar is used for business transactions in most countries, national conventions and government requirements make it important that computer applications accommodate local calendar formats. While there are a number of different calendars, they follow one of three ways of reckoning time:
- Solar: This format is is based on the time it takes the earth to orbit around the sun, approximately 365.2422 days. The Gregorian calendar used in most Western nations is a solar calendar. It was createdin 1582 to replace the less accurate Julian calendar. The Gregorian calendar counts years from the date traditionally held to be the birth of Jesus. The year is sometimes followed by A. D. (for the Latin Anno Domini, or Year of the Lord) or C. E. (for Common Era).
Several other calendar systems use the same month and day format but with a different way of counting years. In Japan, the years are counted based on the reign of the current Emperor (2003 is year 15 of the Heisei Era of the Emperor Akihito). In Taiwan, the years are counted from 1911, when the last emperor of the Qing Dynasty was overthrown and a republic formed (2003 is year 92 for Taiwan). In Thailand, years are numbered from the year traditionally given as the birth of the Buddha, 543 years before the Common Era, making 2003 the year 2546 of the Buddhist Era.
- Lunar: This system is based on the time it takes the moon to orbit the earth, or approximately 29.5306 days. A 12 months lunar year is 354.3672 days. A strictly lunar year lags a solar year by about 11 days every year. The Islamic Hijira calendar is a lunar calendar.
- Lunisolar: A lunisolar system is based primarily on the orbit of the moon, but inserts an additional month, an 'intercalary' month, every 2 or 3 years so that the beginning of the year falls approximately the same time as a solar year. The most common lunisolar model takes advantage of a phenomenon known as the Metonic cycle (named after the 5th Century B. C. E. Greek philosopher Meton, but actually discovered by Chinese astronomers centuries earlier), In the Metonic cycle, 235 lunar months equal almost exactly 19 solar years, so seven additional months are added during each 19- year period. Lunisolar calendars include the Chinese calendar and the Hebrew calendar.
There are also differences in how calendars are presented, including:
- Week start date: Typical calendar formats in North America follow the convention of beginning each week on the left with Sunday, followed by Monday to the right, and so on until Saturday. In many regions (e.g. Europe), the first day of week is Monday. In Islamic cultures, the first day of the week is Saturday, and in the Hebrew calendar, the week begins on Sunday.
- Direction: Days of the week can be displayed from left to right, right to left (in Hebrew or Arabic), or top to bottom (some European calendars).
- Numbering: Days are generally expressed in Arabic digits, but they can also be in other numerals or contains other information.
Presenting calendar information in the customer's preferred format and allowing him or her to enter dates information in their calendar system of choice will enhance the user experience and increase business in many countries. The remainder of this article discusses some of the commonly used calendars in the world. |
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