Millions across the globe this week greeted the start of the new year by tacking up a fresh calendar on their wall, or checking the one installed on their Palm Pilot or computer terminal.
It wasn’t always so simple to track time.
Civilizations have grappled for centuries with the best way to measure the passage of time with varying results. The Gregorian calendar, generally accepted as the main system for calculating time, isn’t the only measuring stick. Chinese, Islamic and Hebrew calendars, among others, still help its users mark time, specifically various holy days and months crucial to their respective faiths.
Calendars fall into two general categories, lunar and solar models. The former, used by Muslims, marks time by the appearance of the moon. Solar calendars, such as the Gregorian system, examine how the Earth revolves around the sun.
Some calendars, like the Chinese calendar, are lunisolar, combining elements of both.
A lunar month, measured by the moon running through its cycles, lasts about 29 1/2 days. Calendars based upon lunar calculations make for 354-day years.
The solar year, which calculates the time the Earth takes to revolve around the sun, clocks in at 365 days, five hours and nearly 49 minutes. That trip is slowing ever so slightly, at a rate of half a second per century.
A day is measured by the rotation of the Earth on its axis, while a seasonal year is counted as the passing of the sun over the Earth’s equator from the Southern to the Northern hemisphere, a time known as the vernal equinox.
The week is considered an artificial construct credited to early Jewish cultures.
The Gregorian calendar, the most dominant model, evolved from Julius Caesar’s Roman calendar, which drew from calculations made in Egyptian cultures and refined by Roman scholars. It originally featured 10 months of alternating 29- and 30-day periods.
Pope Gregory XIII put the finishing touches on what is today’s calendar, based on the Julian calendar that had flourished for more than 1,500 years.
The Gregorian calendar now ran for 356 and a quarter days, an aberration which led the pope to trim 10 days out of October 1582 to restore balance.
He then created leap years, additional days tacked on to February’s 28-day total to complete the balance.
Great Britain and its colonies adopted the calendar named after the pontiff in 1752. By that time, though, the calendar had to be tweaked again, with officials dropping 11 days.
Naeem Baig, secretary general to the Islamic Circle of North America in New York, says the lunar-based Islamic calendar still guides those of the Muslims faith.
“For Muslims around the world it’s important that the calendar should be followed,” says Mr. Baig, whose group supports the practice of Islam through educational classes and positive promotion of the religion.
Its calendar is based on lunar months, a time period that begins with a thin new crescent moon that can be seen in the western sky after sunset.
Ramadan, the holy month of fasting, falls on a different time each year. The holy month began Nov. 16 last year. This year, it will fall about Nov. 6 or 7, he says.
The Islamic calendar’s start date falls on 622 by the Gregorian calendar’s standard. It refers to the year the prophet Mohammed traveled from Mecca to Medina to found the first Islamic community, Mr. Baig says. The trip is known as the Hijrah, which means “to break off from the relations or abandon one’s tribe” in Arabic.
The calendar divides time into 30-year cycles. Nineteen of those years feature 354 days, the remaining 11 have 355 days.
The 12 Islamic months, which have 30 and 29 days, alternately, are Muharram, Safar, Rabi I, Rabi II, Jumada I, Jumada II, Rajab, Shaban, Ramadan, Shawwal, Dhu al-Qa’dah and Dhu al-Hijah.
The current year, according to the Muslim calendar, is 1422.
“For normal business practices, it’s still the Gregorian calendar [which is used],” he says, due to its mass acceptance and accuracy to the Earth’s seasons.
“No Islamic country uses the Islamic calendar for civil use except Saudi Arabia,” says Syed Khalid Shaukat, creator of www.moonsighting.com, which helps Muslims monitor the first visibility of the lunar crescent to better track Islamic time.
While Muslim holy periods like Ramadan shift depending upon the calendar, Jewish religious times have a more structured base, says Marsha Rosenblit, professor of Jewish studies at the University of Maryland College Park.
“Ancient Israelites who developed the calendar didn’t like the idea of having the festival moved around,” she says. “Passover is a spring holiday.”
The Jewish calendar is the official calendar of the Jewish faith and of Israel, she says. It begins with the supposed date of creation, about 3760 years and three months before Christ’s birth.
According to the Hebrew calendar, the year 2002 is considered 5762.
The Hebrew year’s 12 months are Tishri, Heshvan, Kislev, Tevet, Shevat, Adar, Nisan, Iyar, Sivan, Tammuz, Ab and Elul, which are alternately 30 and 29 days.
Days of the week are given numeral titles, except for the seventh day, known as the Sabbath. Days range from sunset to sunset, with the Sabbath beginning at sunset Friday and ending at sunset Saturday.
Seven times during every 19-year period, an extra 29-day month, called Veadar, is inserted between Adar and Nisan to balance out the calendar. During those times, Adar has 30, not 29 days.
With the Chinese calendar, years were originally measured in cycles of 60, with 2000 being the 17th year of the 78th cycle. The 60-year cycles grew less important over time, says David Pankenier, professor of Chinese at Lehigh University in Bethlehem, Pa. Instead, cycles were sometimes measured casually by the length of an emperor’s reign.
The Chinese calendar is a lunisolar model, meaning the months are based on the lunar cycle and leap months are added sporadically to keep it aligned with the solar cycle.
“Over 19 years, an intercalation of seven additional months [is made] to get solar years and lunar year to closely coincide,” Mr. Pankenier says. A true lunar calendar does not include leap months.
That tinkering affects the start of the calendar’s new year.
Chinese New Year typically falls between Jan. 21 and Feb. 21, 45 days after the winter solstice which always falls in the 11th month.
Due to gaps made by lunar calendars, the new year falls about 11 days earlier each year. If that makes the new year begin before Jan. 21, a leap month is installed to push it back into the accepted zone.
Unlike the Muslim calendar, the Chinese model isn’t a strictly lunar construct.
Other global calendars include Indonesian, Tibetan, Indian, Aztec and Mayan. The latter included 18 20-day months, known as vinals.