CALENDAR is a system of organizing days for social, religious, commercial, or administrative purposes. This is done by giving names to periods of time, typically days, weeks, months, and years. The name given to each day is known as a date. Periods in a calendar (such as years and months) are usually, though not necessarily, synchronized with the cycle of the sun or the moon. Many civilizations and societies have devised a calendar, usually derived from other calendars on which they model their systems, suited to their particular needs.

A calendar is also a physical device (often paper). This is the most common usage of the word. Other similar types of calendars can include computerized systems, which can be set to remind the user of upcoming events and appointments.

A calendar can also mean a list of planned events, such as a court calendar.

The English word calendar is derived from the Latin word kalendae, which was the Latin name of the first day of every month.


Celestial bodies ? the Sun, Moon, planets, and stars ? have provided us a reference for measuring the passage of time throughout our existence. Ancient civilizations relied upon the apparent motion of these bodies through the sky to determine seasons, months, and years.

We know little about the details of timekeeping in prehistoric eras, but wherever we turn up records and artifacts, we usually discover that in every culture, some people were preoccupied with measuring and recording the passage of time. Ice-age hunters in Europe over 20,000 years ago scratched lines and gouged holes in sticks and bones, possibly counting the days between phases of the moon. Five thousand years ago, Sumerians in the Tigris-Euphrates valley in today's Iraq had a calendar that divided the year into 30 day months, divided the day into 12 periods (each corresponding to 2 of our hours), and divided these periods into 30 parts (each like 4 of our minutes). We have no written records of Stonehenge, built over 4000 years ago in England, but its alignments show its purposes apparently included the determination of seasonal or celestial events, such as lunar eclipses, solstices and so on.

The earliest Egyptian calendar was based on the moon's cycles, but later the Egyptians realized that the "Dog Star" in Canis Major, which we call Sirius, rose next to the sun every 365 days, about when the annual inundation of the Nile began. Based on this knowledge, they devised a 365 day calendar that seems to have begun around 3100 BCE (Before the Common Era), which thus seems to be one of the earliest years recorded in history.


* 3114 BC Aug 12, - The solar calendar had 365 days divided into 18 months of 20 days each, with a short month of 5 days (considered unlucky days) at the end of each year. The Long Count counted days from a fixed starting point, the 12 August, 3114 BC, which according to the ...For instance, the sacred round which was made up of 260 days per year, was used to plan religious ceremonies. The solar calendar had 365 days divided into 18 months of 20 days each, with a short month of 5 days (considered unlucky days) at the end of each year. The Long Count counted days from a fixed starting point, the 12 August, 3114 BC, which according to the Mayas, was the day the universe began

* 701 BC all calendars appear to have been reorganized. Numa Pompilius, the second king of Rome, reorganized the original calendar of 360 days per year by adding 5 days per year. King Hezekiah, Numa's contemporary, reorganized his Jewish calendar by adding ...In 701 BC, all calendars appear to have been reorganized. Numa Pompilius, the second king of Rome, reorganized the original calendar of 360 days per year by adding 5 days per year. King Hezekiah, Numa's contemporary, reorganized his Jewish calendar by adding a month each Jewish leap year (on a cycle of 7 every 19 years).

* 46 BC - Julius Caesar corrected the calendar in 46 BC prior to the birth of Christ so that in the current Church Age , dates can be determined with reasonable accuracy. The Julian Calendar was very accurate and the Gregorian is even more accurate. Leap year follows the ...Since the Lord Jesus Christ controls history, all the calendars and clocks simply fit into his Plan. This means that the numbers of time have meaning per the clocks and calendars in use at the time. Julius Caesar corrected the calendar in 46 BC prior to the birth of Christ so that in the current Church Age , dates can be determined with reasonable accuracy

* 622 AD Jul 16, - Such concerns apart now, the moment at which the Islamic calendar begins to count, 1 Muharram of the year 1, coincides with Friday, 16 July, 622 AD Of course one can, and indeed should, make similar comparisons with other calendars . For example, it also ...Such concerns apart now, the moment at which the Islamic calendar begins to count, 1 Muharram of the year 1, coincides with Friday, 16 July, 622 AD Of course one can, and indeed should, make similar comparisons with other calendars . For example, it also coincides with the 10th of Ab, 4382, of the Jewish calendar.

* 1582 - Calendars define some notation to identify days in history. The Gregorian calendar, now in wide use, was established by Pope Gregory XIII in AD 1582 as an improvement over the less accurate Julian calendar that had been in use before. Both of these calendars ...Calendars define some notation to identify days in history. The Gregorian calendar, now in wide use, was established by Pope Gregory XIII in AD 1582 as an improvement over the less accurate Julian calendar that had been in use before. Both of these calendars also determine certain holidays. Unfortunately, the new one was not adopted everywhere at the same time


the HISTORY of CALENDARS spans several thousand years. In many early civilizations, calendar systems were developed. For example, in Sumer, the birthplace of the modern sexagesimal system, there were 12 months of 29 or 30 days apiece, much like the modern Gregorian calendar. Mesoamerican cultures also developed their own intricate calendars; the ancient Maya had two separate years?the 260-day Sacred Round, and the 365-day Vague Year. Classical Greek and Roman cultures also developed calendars; the ancient Athenians, for one, had a lunisolar calendar that lasted 364 days, with an intercalary month added every other year. The Romans used two different year lengths; the older one had 304 days divided into 10 months; the newer 365 days divided into 12 months; very much like the modern calendar. They counted years from the founding of Rome, or, sometimes, from the reign of the current consul.

During the early Middle Ages, various local calendars were used in Europe. The presently common Anno Domini system was developed in the 8th century, but the system only became common several centuries later, and even then, rival systems remained in use. Distinct from the rest of Europe, the Scandinavian Vikings maintained their own calendar during this time, which was divided into two seasons; summer and winter. A definition of the calendar day resembling the modern one was first stated in the latter part of the 13th century.

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the SUMERIAN CALENDAR
... The ancient Sumerian calendar divided a year into 12 lunar months of 29 or 30 days.
Each month began with the sighting of a new moon.
Sumerian months had no uniform name throughout Sumeria because of the religious diversity. This resulted in scribes and scholars referring to them as "the first month", "the fifth month" etc.
To keep the lunar year of 354 days in step with the solar year of 365.25 days an extra month was added periodically, much like a Gregorian leap year. Also, every six years the sumerian calendar included an extra month of 62 days.
There were no weeks in the Sumerian calendar.
Holy days and time off from work were usually celebrated on the first, seventh and fifteenth of each month. In addition to these holy days, there were also feast days which varied from city to city.
A day was divided into twelve hours, six daylight hours, each lasting one-sixth of the day, and six nighttime hours, each lasting one-sixth of the night. This meant the length of hours varied from season to season, daylight hours being shorter in the winter and longer in the summer and vice versa


the BABYLONIAN CALENDAR
... was a lunisolar calendar with years consisting of 12 lunar months, each beginning when a new crescent moon was first sighted low on the western horizon at sunset, plus an intercalary month inserted as needed by decree. The calendar is based on a Sumerian (Ur III) precedecessor preserved in the Umma calendar of Shulgi (c. 21st century BC).


the MAYA CALENDAR
... Of all the ancient calendar systems, the [Maya civilization|Maya] and other Mesoamerican systems are the most complex. The Mayan calendar had 2 years, the 260-day Sacred Round, or tzolkin, and the 365-day Vague Year, or haab.

A modern pictogram of the Mayan god Ahau, after which the 20th day of the tzolkin cycle was namedThe Sacred Round of 260 days is composed of two smaller cycles: the numbers 1 through 13, coupled with 20 different day names, mostly the names of gods: Imix, Ik, Akbal, Kan, Chicchan, Cimi, Manik, Lamat, Muluc, Oc, Chuen, Eb, Ben, Ix, Men, Cib, Caban, Eiznab, Cauac, and Ahau. The Sacred Round was used to determine important activities related to the gods and humans: name individuals, predict the future, decide on auspicious dates for battles, marriages, and so on.

The two cycles of 13 and 20 intermesh and are repeated without interruption: the cycle would begin with 1 Imix, then 2 Ik, then 3 Akbal and so on until the number 13 was reached, at which point the number cycle was restarted so 13 Ben would be followed by 1 Ix, 2 Men and so on. This time Imix would be numbered 8. The cycle ended after 260 days, with the last day being 13 Ahau.

The Vague Year of 365 days is similar to our modern calendar, consisting of 18 months of 20 days each, with an unlucky five day period at the end. The Vague Year had to do primarily with the seasons and agriculture, and was based on the solar cycle. The 18 Maya months are known, in order, as: Pop, Uo, Zip, Zotz, Tzec, Xuc, Yaxkin, Mol, Chen, Yax, Zac, Ceh, Mac, Kankin, Maun, Pax, Kayab and Cumku. The unlucky five-day period was known as uayeb, and was considered a time which could hold danger, death and bad luck


the HEBREW CALENDAR
... or Jewish calendar, is a lunisolar calendar used today predominantly for Jewish religious observances. It determines the dates for Jewish holidays and the appropriate public reading of Torah portions, yahrzeits (dates to commemorate the death of a relative), and daily Psalm reading, among many ceremonial uses. In Israel, it is an official calendar for civil purposes and provides a time frame for agriculture.

Originally the Hebrew calendar was used by Jews for all daily purposes, but following the conquest of Jerusalem by Pompey in 63 BCE (see also Iudaea province), Jews began additionally following the imperial civil calendar, which was decreed in 45 BCE, for civic matters such as the payment of taxes and dealings with government officials.

The Hebrew calendar has evolved over time. For example, until the Tannaitic period, the months were set by observation of a new crescent moon, with an additional month added every two or three years to keep Passover in the spring, again based on observation of natural events, namely the ripening of barley to reach the stage of "aviv" (nearly ripened crop). Through the Amoraic period and into the Geonic period, this system was displaced by mathematical rules. The principles and rules appear to have been settled by the time Maimonides compiled the Mishneh Torah in the 12th century.

Because of the roughly eleven-day difference between twelve lunar months and one solar year, the length of the Hebrew calendar year varies in a repeating 19-year Metonic cycle of 235 lunar months, with an intercalary lunar month added according to defined rules every two or three years, for a total of 7 times per 19 years. Seasonal references in the Hebrew calendar reflect its development in the region east of the Mediterranean and the times and climate of the Northern Hemisphere. The Hebrew calendar year is longer by about 6 minutes and 25+25/57 seconds than the present-day mean solar year, so that every 224 years, the Hebrew calendar will fall a full day behind the modern solar year, and about every 231 years it will fall a full day behind the Gregorian calendar year.

The present counting method for years use the Anno Mundi epoch, abbreviated AM or A.M. and also referred to as the Hebrew era. Hebrew year 5770 began on 19 September 2009 and ended on 8 September 2010. Hebrew year 5771 (a leap year) began on 9 September 2010 and ends on 28 September 2011


the ASSYRIAN CALENDAR
... is a lunar-based calendar that begins in the year 4750 BC, inspired by an estimate of the date of the first temple at Ashur, notably based on a series of articles published in the Assyrian magazine Gilgamesh, edited by the brothers Addi and Jean Alkhas and Nimrod Simono. The year begins with the first sight of Spring. The Assyrian new year is still celebrated every year with festivals and gatherings. As of April 1, 2010, it is the Assyrian year of 6760.


the ZOROASTRIAN CALENDAR
... is a religious Iranian calendar used by adherents of the Zoroastrian faith, and is an approximation of the tropical solar calendar. To this day, Zoroastrians, irrespective of geographic location, adhere to variations of this ancient Iranian calendar for religious purposes

Prior to the particular Zoroastrian calendar pertaining to the royal Shah dynasty, a common use of a 360-day year existed simultaneously since At least the mid-5 Th century BCE and estimated that at the time of Final Judgement the two systems would be out of sync by four years.

In 1006, the roaming New Year's Day once again coincided with the day of the vernal equinox, and (according to legend) it was resolved that the Zoroastrian calendar henceforth intercalate an additional month every 120 years as prescribed in Denkard III.419 (it must however be noted that the Denkard is itself a 9th century work). At some point between 1125 and 1250, the Parsi-Zoroastrians of the Indian subcontinent inserted such an embolismic month, named Aspandarmad vahizak (the month of Aspandarmad but with a vahizak suffix). That month would also be the last month intercalated: subsequent generations of Parsis neglected to insert a thirteenth month


the ISLAMIC CALENDAR
... is a lunar calendar consisting of 12 lunar months in a year of 354 or 355 days. It is used to date events in many Muslim countries (concurrently with the Gregorian calendar), and used by Muslims everywhere to determine the proper day on which to celebrate Islamic holy days and festivals. The first year was the year during which the emigration of the Islamic prophet Muhammad from Mecca to Medina, known as the Hijra, occurred. Each numbered year is designated either H for Hijra or AH for the Latin anno Hegirae (in the year of the Hijra). A limited number of years before Hijra (BH) are used to date events related to Islam, such as the birth of Muhammad in 53 BH.
The current Islamic year is 1432 AH, from approximately 7 December 2010 (evening) to 26 November 2011 (evening).

Being a purely lunar calendar, it is not synchronized with the seasons. With an annual drift of 11 or 12 days, the seasonal relation repeats about every 33 Islamic years.


the ROMAN CALENDAR
... changed its form several times in the time between the founding of Rome and the fall of the Roman Empire. This article generally discusses the early Roman or 'pre-Julian' calendars
The original Roman calendar is believed to have been a lunar calendar, which may have been based on one of the Greek lunar calendars. As the time between new moons averages 29.5 days, its months were constructed to be either hollow (29 days) or full (30 days). Full months were considered powerful and therefore auspicious; hollow months were unlucky. Unlike currently used dates, which are numbered sequentially from the beginning of the month, the Romans counted backwards from three fixed points: the Nones, the Ides and the Kalends of the following month. This system originated in the practice of "calling" the new month when the lunar crescent was first observed in the west after sunset. From the shape and orientation of the new moon, the number of days remaining to the nones would be proclaimed.

Roman writers claimed that their calendar was invented by Romulus, the founder of Rome around 753 BC. His version contained ten months with the vernal equinox in the first month. However, his months were not lunar:

The calendar year lasted 304 days and there were about 61 days of winter which were not assigned to any month. The later months were named based on their position in the calendar: Quintilis comes from quinque (meaning five), Sextilis from sex (meaning six), September from septem (meaning seven), October from octo (meaning eight), November from novem (meaning nine) and December from decem (meaning ten).


the JULIAN CALENDAR
... began in 45 BC (709 AUC) as a reform of the Roman calendar by Julius Caesar. It was chosen after consultation with the astronomer Sosigenes of Alexandria and was probably designed to approximate the tropical year (known at least since Hipparchus).

The Julian calendar has a regular year of 365 days divided into 12 months with a leap day added to February every four years. The Julian year is, therefore, on average 365.25 days long. The motivation for most calendars is to fix the number of days between return of the cycle of seasons (from Spring equinox to the next Spring equinox, for example), so that the calendar could be used as an aid to planting and other season-related activities. The cycle of seasons (tropical year) had been known since ancient times to be about 365 and 1/4 days long.

The more modern Gregorian calendar eventually superseded the Julian calendar: the reason is that a tropical year (or solar year) is actually about 11 minutes shorter than 365.25 days. These extra 11 minutes per year in the Julian calendar caused it to gain about three days every four centuries, when compared to the observed equinox times and the seasons. In the Gregorian calendar system, first proposed in the 16th century, this problem was dealt with by dropping some calendar days, in order to realign the calendar and the equinox times. Subsequently, the Gregorian calendar drops three leap year days across every four centuries.

The Julian calendar remained in use into the 20th century in some countries as a civil calendar, but has been replaced by the Gregorian calendar in nearly all countries. The Roman Catholic Church, the Eastern Rite Catholic Churches and Protestant churches have replaced the Julian calendar with the Gregorian calendar; however, the Orthodox Church (with the exception of Romania, Estonia and Finland) still use the Julian calendar for calculating the dates of moveable feasts. Some Orthodox churches have adopted the Revised Julian calendar for the observance of fixed feasts, while other Orthodox churches retain the Julian calendar for all purposes. The Julian calendar is still used by the Berber people of North Africa, and on Mount Athos.

The notation "Old Style" (OS) is sometimes used to indicate a date in the Julian calendar, as opposed to "New Style" (NS), which either represents the Julian date with the start of the year as 1 January or a full mapping onto the Gregorian calendar. This notation is used in reference to dates from tsarist Russia (the country did not switch to the new calendar until 1918).


the GREGORIAN CALENDAR
... also known as the Western calendar, or Christian calendar, is the internationally accepted civil calendar. It was introduced by Pope Gregory XIII, after whom the calendar was named, by a decree signed on 24 February 1582, a papal bull known by its opening words Inter gravissimas. The reformed calendar was adopted later that year by a handful of countries, with other countries adopting it over the following centuries. The motivation for the Gregorian reform was that the Julian calendar assumes that the time between vernal equinoxes is 365.25 days, when in fact it is about 11 minutes less. The error between these values was about 10 days, accumulated at the rate of about three days every four centuries, resulting in the equinox occurring on March 11 and moving steadily earlier in the calendar, by the time of the reform. Since the equinox was tied to the celebration of Easter, the Roman Catholic Church considered that this steady movement was undesirable.

The Gregorian calendar reform contained two parts, a reform of the Julian calendar as used up to Pope Gregory's time, together with a reform of the lunar cycle used by the Church along with the Julian calendar for calculating dates of Easter. The reform was a modification of a proposal made by the Calabrian doctor Aloysius Lilius (or Lilio). Lilius' proposal included reducing the number of leap years in four centuries from 100 to 97, by making 3 out of 4 centurial years common instead of leap years: this part of the proposal had been suggested before by, among others, Pietro Pitati. Lilio also produced an original and practical scheme for adjusting the epacts of the moon for completing the calculation of Easter dates, solving a long-standing difficulty that had faced proposers of calendar reform.

The Gregorian calendar continued the previous year-numbering system (Anno Domini), which counts years from the traditional Incarnation of Jesus, and which had spread throughout Europe during the Middle Ages. This year-numbering system is the predominant international standard today.

The Origins of English naming used by the Gregorian calendar

* January: Janus (Roman god of gates, doorways, beginnings & endings)

* February: Februus (Etruscan god of death) Februarius (mensis) (Latin for "month of purification (rituals)" it is said to be a Sabine word, the last month of ancient pre-450 BC Roman calendar). It is related to fever.

* March: Mars (Roman god of war)

* April: "Modern scholars associate the name with an ancient root meaning 'other', i.e the second month of a year beginning in March."

* May: Maia Maiestas (Roman goddess)

* June: Juno (Roman goddess, wife of Jupiter)

* July: Julius Caesar (Roman dictator) (month was formerly named Quintilis, the fifth month of the calendar of Romulus)

* August: Augustus (first Roman emperor) (month was formerly named Sextilis, the sixth month of Romulus)

* September: septem (Latin for seven, the seventh month of Romulus)

* October: octo (Latin for eight, the eighth month of Romulus)

* November: novem (Latin for nine, the ninth month of Romulus)

* December: decem (Latin for ten, the tenth month of Romulus)


these are the PROPOSED REFORMS of the Gregorian calendar:

Holocene calendar

International Fixed Calendar
- (also called the International Perpetual calendar)

World Calendar

World Season Calendar

Leap week calendars
1/ Pax Calendar
2/ Common-Civil-Calendar-and-Time
3/ Symmetry454