Muslim Calendar

Muslim Calendar

The Muslim calendar (also called the Islamic calendar, or Hijrah) is a dating system used in the Muslim world that is based on a year of 12 months. Each month begins with the sighting of the crescent of the new moon as it emerges from eclipse. The months of the Muslim calendar are Muharram, Safar, Rabi I, Rabi II, Jumada I, Jumada II, Rajab, ShaAban, Ramadan, Shawwal, Dhu al-QaAdah, and Dhu al- Hijjah.
In the standard Muslim calendar the months are alternately 30 and 29 days long except for the 12th month, Dhu al-Hijjah, the length of which is varied in a 30-year cycle intended to keep the calendar in step with the true phases of the Moon. In 11 years of this cycle, Dhu al-Hijjah has 30 days, and in the other 19 years it has 29. Thus the year has either 354 or 355 days. No months are intercalated, so that the named months do not remain in the same seasons but retrogress through the entire solar, or seasonal, year (of about 365.25 days) every 32.5 solar years.

There are some exceptions to this calendar in the Muslim world. Turkey uses the Gregorian calendar, while the Iranian Muslim calendar is based on a solar year. The Iranian calendar still begins from the same dating point as other Muslim calendars—that is, some 10 years prior to the death of Muhammad in AD 632. Thus, the Gregorian year AD 2010 corresponds to the Hijrah years of AH 1431–32.

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Jewish Calendar

Jewish Calendar

The Jewish calendar is lunisolar—i.e., regulated by the positions of both the Moon and the Sun. It consists usually of 12 alternating lunar months of 29 and 30 days each (except for Heshvan and Kislev, which sometimes have either 29 or 30 days), and totals 353, 354, or 355 days per year.The average lunar year (354 days) is adjusted to the solar year (365¼ days) by the periodic introduction of leap years in order to assure that the major festivals fall in their proper season. The leap year consists of an additional 30-day month called First Adar, which always precedes the month of (Second) Adar. (During leap year, the Adar holidays are postponed to Second Adar.) A leap year consists of either 383, 384, or 385 days and occurs seven times during every 19-year period (the so-called Metonic cycle). Among the consequences of the lunisolar structure are these: (1) The number of days in a year may vary considerably, from 353 to 385 days. (2)The first day of a month can fall on any day of the week, that day varying from year to year. Consequently, the days of the week upon which an annual Jewish festival falls vary from year to year despite the festival’s fixed position in the Jewish month. The months of the Jewish calendar and their Gregorian equivalents are as follows:

JEWISH MONTH GREGORIAN MONTH(S)
Tishri September–October
Heshvan, or Marheshvan October–November
Kislev November–December
Tevet December–January
Shevat January–February
Adar February–March
Nisan March–April
Iyyar April–May
Sivan May–June
Tammuz June–July
Av July–August
Elul August–September

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Julian and Gregorian Calendars

Julian and Gregorian Calendars

The Julian calendar, also called the Old Style calendar, is a dating system established by Julius Caesar as a reform of the Roman republican calendar. Caesar, advised by the Alexandrian astronomer Sosigenes, made the new calendar solar, not lunar, and he took the length of the solar year as 365¼ days. The year was divided into 12 months, all of which had either 30 or 31 days except February, which contained 28 days in common (365-day) years and 29 in every fourth year (a leap year, of 366 days). Because of misunderstandings, the calendar was not established in smooth operation until AD 8. Further, Sosigenes had overestimated the length of the year by 11 minutes 14 seconds, and by the mid-1500s, the cumulative effect of this error had shifted the dates of the seasons by about 10 days from Caesar’s time.
This inaccuracy led Pope Gregory XIII to reform the Julian calendar. His Gregorian calendar, also called the New Style calendar, is still in general use. Gregory’s proclamation in 1582 restored the calendar to the seasonal dates of AD 325, an adjustment of 10 days. Although the amount of regression was some 14 days by Pope Gregory’s time, Gregory based his reform on restoration of the vernal equinox, then falling on 11 March, to the date (21 March) it had in AD 325, the time of the Council of Nicaea. Advancing the calendar 10 days after 4 Oct 1582, the day following being reckoned as 15 October, effected the
change.
The Gregorian calendar differs from the Julian only in that no century year is a leap year unless it is exactly divisible by 400 (e.g., 1600, 2000). A further refinement, the designation of years evenly divisible by 4,000 as common (not leap) years, will keep the Gregorian calendar accurate to within one day in 20,000 years.

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Daylight Saving Time

Daylight Saving Time

Also called summer time, daylight saving time is a system for uniformly advancing clocks, especially in summer, so as to extend daylight hours during conventional waking time. In the Northern Hemisphere, clocks are usually set ahead one hour in late March or in April and are set back one hour in late September or in October; most Southern Hemisphere countries that observe daylight saving time set clocks ahead in October or November and reset them in March or April. Equatorial countries do not observe daylight saving time because daylight hours stay about the same from season to season in the lower latitudes. The practice was first suggested in a whimsical essay by Benjamin Franklin in 1784. In 1907 an Englishman,William Willett, campaigned for setting the clock ahead by 80 minutes in four moves of 20 minutes each during the spring and summer months. In 1908 the British House of Commons rejected a bill to advance the clock by one hour in the spring and return Greenwich Mean (standard) Time in the autumn. Several countries, including Australia, Great Britain,Germany, and the United States, adopted summer daylight saving time during World War I to conserve fuel by reducing the need for artificial light. During World War II, clocks were kept continuously advanced by an hour in some nations—for instance, in the US from 9 Feb 1942 to 30 Sep 1945—and England used “double summer time” during part of the year, advancing clocks two hours from the standard time during the summer and one hour during the winter months. In 2005 the US Congress changed the law governing daylight saving time, moving the start of daylight saving time from the first Sunday in April to the second Sunday in March, while moving the end date from the last Sunday in October to the first Sunday in November starting in 2007. In most of the countries of Western Europe, daylight saving time starts on the last Sunday in March and ends on the last Sunday in October.

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