A 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. A date is the designation of a single, specific day within such a system. A calendar is also a physical record (often paper) of such a system. A calendar can also mean a list of planned events, such as a court calendar or a partly or fully chronological list of documents, such as a calendar of wills.

Periods in a calendar (such as years and months) are usually, though not necessarily, synchronised with the cycle of the sun or the moon. The most common type of pre-modern calendar was the lunisolar calendar, a lunar calendar that occasionally adds one intercalary month to remain synchronised with the solar year over the long term.

The term calendar is taken from calendae, the term for the first day of the month in the Roman calendar, related to the verb calare "to call out", referring to the "calling" of the new moon when it was first seen.[1] Latin calendarium meant "account book, register" (as accounts were settled and debts were collected on the calends of each month). The Latin term was adopted in Old French as calendier and from there in Middle English as calender by the 13th century (the spelling calendar is early modern). A calendar can be on paper or electronic device.

01 02 03 04 05 06
07 08 09 10 11 12 13
14 15 16 17 18 19 20
21 22 23 24 25 26 27
28 29 30  


Equinozio da Pizzo Vento,tramonto fondachelli fantina, sicilia
Equinox seen from the astronomic calendar of Pizzo Vento at Fondachelli Fantina, Sicily

The course of the sun and the moon are the most salient natural, regularly recurring events useful for timekeeping, thus in pre-modern societies worldwide lunation and the year were most commonly used as time units. Nevertheless, the Roman calendar contained remnants of a very ancient pre-Etruscan 10-month solar year.[2] The first recorded physical calendars, dependent on the development of writing in the Ancient Near East, are the Bronze Age Egyptian and Sumerian calendars.[3]

A large number of Ancient Near East calendar systems based on the Babylonian calendar date from the Iron Age, among them the calendar system of the Persian Empire, which in turn gave rise to the Zoroastrian calendar and the Hebrew calendar.[4]

A great number of Hellenic calendars developed in Classical Greece, and in the Hellenistic period gave rise to both the ancient Roman calendar and to various Hindu calendars.[5]

Calendars in antiquity were lunisolar, depending on the introduction of intercalary months to align the solar and the lunar years. This was mostly based on observation, but there may have been early attempts to model the pattern of intercalation algorithmically, as evidenced in the fragmentary 2nd-century Coligny calendar.

The Roman calendar was reformed by Julius Caesar in 45 BC. The Julian calendar was no longer dependent on the observation of the new moon but simply followed an algorithm of introducing a leap day every four years. This created a dissociation of the calendar month from the lunation.

The Islamic calendar is based on the prohibition of intercalation (nasi') by Muhammad, in Islamic tradition dated to a sermon held on 9 Dhu al-Hijjah AH 10 (Julian date: 6 March 632). This resulted in an observation-based lunar calendar that shifts relative to the seasons of the solar year.

Modern reforms

The first calendar reform of the early modern era was the Gregorian calendar, introduced in 1582 based on the observation of a long-term shift between the Julian calendar and the solar year.

There have been a number of modern proposals for reform of the calendar, such as the World Calendar, International Fixed Calendar, Holocene calendar, and, recently, the Hanke-Henry Permanent Calendar. Such ideas are mooted from time to time but have failed to gain traction because of the loss of continuity, massive upheaval in implementation, and religious objections.

Calendar systems

A full calendar system has a different calendar date for every day. Thus the week cycle is by itself not a full calendar system; neither is a system to name the days within a year without a system for identifying the years.

The simplest calendar system just counts time periods from a reference date. This applies for the Julian day or Unix Time. Virtually the only possible variation is using a different reference date, in particular, one less distant in the past to make the numbers smaller. Computations in these systems are just a matter of addition and subtraction.

Other calendars have one (or multiple) larger units of time.

Calendars that contain one level of cycles:

  • week and weekday – this system (without year, the week number keeps on increasing) is not very common
  • year and ordinal date within the year, e.g., the ISO 8601 ordinal date system

Calendars with two levels of cycles:

Cycles can be synchronized with periodic phenomena:

Sun and Moon Nuremberg chronicle
Sun and Moon, Schedel's Nuremberg Chronicle, 1493

Very commonly a calendar includes more than one type of cycle, or has both cyclic and non-cyclic elements.

Most calendars incorporate more complex cycles. For example, the vast majority of them track years, months, weeks and days. The seven-day week is practically universal, though its use varies. It has run uninterrupted for millennia.[6]

Solar calendars

Solar calendars assign a date to each solar day. A day may consist of the period between sunrise and sunset, with a following period of night, or it may be a period between successive events such as two sunsets. The length of the interval between two such successive events may be allowed to vary slightly during the year, or it may be averaged into a mean solar day. Other types of calendar may also use a solar day.

Lunar calendars

Not all calendars use the solar year as a unit. A lunar calendar is one in which days are numbered within each lunar phase cycle. Because the length of the lunar month is not an even fraction of the length of the tropical year, a purely lunar calendar quickly drifts against the seasons, which do not vary much near the equator. It does, however, stay constant with respect to other phenomena, notably tides. An example is the Islamic calendar. Alexander Marshack, in a controversial reading,[7] believed that marks on a bone baton (c. 25,000 BC) represented a lunar calendar. Other marked bones may also represent lunar calendars. Similarly, Michael Rappenglueck believes that marks on a 15,000-year-old cave painting represent a lunar calendar.[8]

Lunisolar calendars

A lunisolar calendar is a lunar calendar that compensates by adding an extra month as needed to realign the months with the seasons. An example is the Hebrew calendar which uses a 19-year cycle.

Calendar subdivisions

Nearly all calendar systems group consecutive days into "months" and also into "years". In a solar calendar a year approximates Earth's tropical year (that is, the time it takes for a complete cycle of seasons), traditionally used to facilitate the planning of agricultural activities. In a lunar calendar, the month approximates the cycle of the moon phase. Consecutive days may be grouped into other periods such as the week.

Because the number of days in the tropical year is not a whole number, a solar calendar must have a different number of days in different years. This may be handled, for example, by adding an extra day in leap years. The same applies to months in a lunar calendar and also the number of months in a year in a lunisolar calendar. This is generally known as intercalation. Even if a calendar is solar, but not lunar, the year cannot be divided entirely into months that never vary in length.

Cultures may define other units of time, such as the week, for the purpose of scheduling regular activities that do not easily coincide with months or years. Many cultures use different baselines for their calendars' starting years. For example, the year in Japan is based on the reign of the current emperor: 2006 was Year 18 of the Emperor Akihito.

Other calendar types

Arithmetic and astronomical calendars

JudischerKalender-1831 ubt.jpeg
Calendar of the Qahal, 5591 (1831)

An astronomical calendar is based on ongoing observation; examples are the religious Islamic calendar and the old religious Jewish calendar in the time of the Second Temple. Such a calendar is also referred to as an observation-based calendar. The advantage of such a calendar is that it is perfectly and perpetually accurate. The disadvantage is that working out when a particular date would occur is difficult.

An arithmetic calendar is one that is based on a strict set of rules; an example is the current Jewish calendar. Such a calendar is also referred to as a rule-based calendar. The advantage of such a calendar is the ease of calculating when a particular date occurs. The disadvantage is imperfect accuracy. Furthermore, even if the calendar is very accurate, its accuracy diminishes slowly over time, owing to changes in Earth's rotation. This limits the lifetime of an accurate arithmetic calendar to a few thousand years. After then, the rules would need to be modified from observations made since the invention of the calendar.

Complete and incomplete calendars

Calendars may be either complete or incomplete. Complete calendars provide a way of naming each consecutive day, while incomplete calendars do not. The early Roman calendar, which had no way of designating the days of the winter months other than to lump them together as "winter", is an example of an incomplete calendar, while the Gregorian calendar is an example of a complete calendar.

Calendars in use

The primary practical use of a calendar is to identify days: to be informed about or to agree on a future event and to record an event that has happened. Days may be significant for agricultural, civil, religious or social reasons. For example, a calendar provides a way to determine when to start planting or harvesting, which days are religious or civil holidays, which days mark the beginning and end of business accounting periods, and which days have legal significance, such as the day taxes are due or a contract expires. Also a calendar may, by identifying a day, provide other useful information about the day such as its season.

Calendars are also used to help people manage their personal schedules, time and activities, particularly when individuals have numerous work, school, and family commitments. People frequently use multiple systems, and may keep both a business and family calendar to help prevent them from overcommitting their time.

Calendars are also used as part of a complete timekeeping system: date and time of day together specify a moment in time. In the modern world, timekeepers can show time, date and weekday. Some may also show lunar phase.

Gregorian calendar

The Gregorian calendar is the de facto international standard, and is used almost everywhere in the world for civil purposes. It is a purely solar calendar, with a cycle of leap days in a 400-year cycle designed to keep the duration of the year aligned with the solar year.

Each Gregorian year has either 365 or 366 days (the leap day being inserted as 29 February), amounting to an average Gregorian year of 365.2425 days (compared to a solar year of 365.2422 days). It was introduced in 1582 as a refinement to the Julian calendar which had been in use throughout the European Middle Ages, amounting to a 0.002% correction in the length of the year.

During the Early Modern period, however, its adoption was mostly limited to Roman Catholic nations, but by the 19th century, it became widely adopted worldwide for the sake of convenience in international trade. The last European country to adopt the reform was Greece, in 1923.

The calendar epoch used by the Gregorian calendar is inherited from the medieval convention established by Dionysius Exiguus and associated with the Julian calendar. The year number is variously given as AD (for Anno Domini) or CE (for Common Era or, indeed, Christian Era).

Religious calendars

Hindu calendar 1871-72
A Hindu almanac (pancanga) for the year 1871/2 from Rajasthan (Library of Congress, Asian Division)

The most important use of pre-modern calendars is keeping track of the liturgical year and the observation of religious feast days.

While the Gregorian calendar is itself historically motivated in relation to the calculation of the Easter date, it is now in worldwide secular use as the de facto standard. Alongside the use of the Gregorian calendar for secular matters, there remain a number of calendars in use for religious purposes.

Eastern Christians, including the Orthodox Church, use the Julian calendar.

The Islamic calendar or Hijri 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 most of the 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. Its epoch is the Hijra (corresponding to AD 622) With an annual drift of 11 or 12 days, the seasonal relation is repeated approximately each 33 Islamic years.

Various Hindu calendars remain in use in the Indian subcontinent, including the Nepali calendar, Bengali calendar, Malayalam calendar, Tamil calendar, Vikrama Samvat used in Northern India, and Shalivahana calendar in the Deccan states.

The Buddhist calendar and the traditional lunisolar calendars of Cambodia, Laos, Myanmar, Sri Lanka and Thailand are also based on an older version of the Hindu calendar.

Most of the Hindu calendars are inherited from a system first enunciated in Vedanga Jyotisha of Lagadha, standardized in the Sūrya Siddhānta and subsequently reformed by astronomers such as Āryabhaṭa (AD 499), Varāhamihira (6th century) and Bhāskara II (12th century).

The Hebrew calendar is used by Jews worldwide for religious and cultural affairs, also influences civil matters in Israel (such as national holidays) and can be used there for business dealings (such as for the dating of cheques).

Bahá'ís worldwide use the Bahá'í calendar.The Baha'i Calendar, also known as the Badi Calendar was first established by the Bab in the Kitab-i-Asma. The Baha'i Calendar is also purely a solar calendar and comprises 19 months each having nineteen days.

National calendars

The Chinese, Hebrew, Hindu, and Julian calendars are widely used for religious and social purposes.

The Iranian (Persian) calendar is used in Iran and some parts of Afghanistan. The Ethiopian calendar or Ethiopic calendar is the principal calendar used in Ethiopia and Eritrea, with the Oromo calendar also in use in some areas. In neighboring Somalia, the Somali calendar co-exists alongside the Gregorian and Islamic calendars. In Thailand, where the Thai solar calendar is used, the months and days have adopted the western standard, although the years are still based on the traditional Buddhist calendar.

Fiscal calendars

Pieter Brueghel the Younger (or workshop) The Payment of the Tithes Bonhams
The Payment of the Tithes (The tax-collector), also known as Village Lawyer, by Pieter Brueghel the Younger or workshop

A fiscal calendar generally means the accounting year of a government or a business. It is used for budgeting, keeping accounts and taxation. It is a set of 12 months that may start at any date in a year. The US government's fiscal year starts on 1 October and ends on 30 September. The government of India's fiscal year starts on 1 April and ends on 31 March. Small traditional businesses in India start the fiscal year on Diwali festival and end the day before the next year's Diwali festival.

In accounting (and particularly accounting software), a fiscal calendar (such as a 4/4/5 calendar) fixes each month at a specific number of weeks to facilitate comparisons from month to month and year to year. January always has exactly 4 weeks (Sunday through Saturday), February has 4 weeks, March has 5 weeks, etc. Note that this calendar will normally need to add a 53rd week to every 5th or 6th year, which might be added to December or might not be, depending on how the organization uses those dates. There exists an international standard way to do this (the ISO week). The ISO week starts on a Monday, and ends on a Sunday. Week 1 is always the week that contains 4 January in the Gregorian calendar.


Petaluma and Santa Rosa Railroad Co. Calendar
A calendar from the Petaluma and Santa Rosa Railroad

The term calendar applies not only to a given scheme of timekeeping but also to a specific record or device displaying such a scheme, for example an appointment book in the form of a pocket calendar (or personal organizer), desktop calendar, a wall calendar, etc.

In a paper calendar one or two sheets can show a single day, a week, a month, or a year. If a sheet is for a single day, it easily shows the date and the weekday. If a sheet is for multiple days it shows a conversion table to convert from weekday to date and back. With a special pointing device, or by crossing out past days, it may indicate the current date and weekday. This is the most common usage of the word.

In the US Sunday is considered the first day of the week and so appears on the far left and Saturday the last day of the week appearing on the far right. In Britain the weekend may appear at the end of the week so the first day is Monday and the last day is Sunday. The US calendar display is also used in Britain.

It is common to display the Gregorian calendar in separate monthly grids of seven columns (from Monday to Sunday, or Sunday to Saturday depending on which day is considered to start the week – this varies according to country) and five to six rows (or rarely, four rows when the month of February contains 28 days beginning on the first day of the week), with the day of the month numbered in each cell, beginning with 1. The sixth row is sometimes eliminated by marking 23/30 and 24/31 together as necessary.

When working with weeks rather than months, a continuous format is sometimes more convenient, where no blank cells are inserted to ensure that the first day of a new month begins on a fresh row.

Calendaring software

Calendaring software provides users with an electronic version of a calendar, and may additionally provide an appointment book, address book or contact list. Calendaring is a standard feature of many PDAs, EDAs, and smartphones. The software may be a local package designed for individual use (e.g., Lightning extension for Mozilla Thunderbird, Microsoft Outlook without Exchange Server, or Windows Calendar) or may be a networked package that allows for the sharing of information between users (e.g., Mozilla Sunbird, Windows Live Calendar, Google Calendar, or Microsoft Outlook with Exchange Server).

See also



  1. ^ New Shorter Oxford English Dictionary
  2. ^ "Religion in the Etruscan period" in Roman religion in Encyclopædia Britannica
  3. ^ citation needed
  4. ^ citation needed
  5. ^ citation needed
  6. ^ Zerubavel 1985.
  7. ^ James Elkins, Our beautiful, dry, and distant texts (1998) 63ff.
  8. ^ "Oldest lunar calendar identified". BBC News. 16 October 2000. Retrieved 14 March 2013.


  • "calendar", American Heritage Dictionary (5th ed.), 2017
  • Birashk, Ahmad (1993), A comparative Calendar of the Iranian, Muslim Lunar, and Christian Eras for Three Thousand Years, Mazda Publishers, ISBN 978-0-939214-95-2
  • Björnsson, Árni (1995) [1977], High Days and Holidays in Iceland, Reykjavík: Mál og menning, ISBN 978-9979-3-0802-7, OCLC 186511596
  • Dershowitz, Nachum; Reingold, Edward M (1997), Calendrical Calculations, Cambridge University Press, ISBN 978-0-521-56474-8, archived from the original on 17 October 2002 with Online Calculator
  • Doggett, LE (1992), "Calendars", in Seidelmann, P. Kenneth (ed.), Explanatory Supplement to the Astronomical Almanac, University Science Books, ISBN 978-0-935702-68-2, archived from the original on 1 April 2004
  • Richards, EG (1998), Mapping Time, the calendar and its history, Oxford University Press, ISBN 978-0-19-850413-9
  • Rose, Lynn E (1999), Sun, Moon, and Sothis, Kronos Press, ISBN 978-0-917994-15-9
  • Schuh, Dieter (1973), Untersuchungen zur Geschichte der Tibetischen Kalenderrechnung (in German), Wiesbaden: Franz Steiner Verlag, OCLC 1150484
  • Spier, Arthur (1986), The Comprehensive Hebrew Calendar, Feldheim Publishers, ISBN 978-0-87306-398-2
  • Zerubavel, Eviatar (1985), The Seven Day Circle: The History and Meaning of the Week, University of Chicago Press, ISBN 978-0-226-98165-9

Further reading

  • Fraser, Julius Thomas (1987), Time, the Familiar Stranger (illustrated ed.), Amherst: Univ of Massachusetts Press,, ISBN 978-0-87023-576-4, OCLC 15790499
  • Whitrow, Gerald James (2003), What is Time?, Oxford: Oxford University Press, ISBN 978-0-19-860781-6, OCLC 265440481
  • C.K, Raju (2003), The Eleven Pictures of Time, SAGE Publications Pvt. Ltd, ISBN 978-0-7619-9624-8
  • C.K, Raju (1994), Time: Towards a Consistent Theory, Springer, ISBN 978-0-7923-3103-2

External links

Anno Domini

The terms anno Domini (AD) and before Christ (BC) are used to label or number years in the Julian and Gregorian calendars. The term anno Domini is Medieval Latin and means "in the year of the Lord", but is often presented using "our Lord" instead of "the Lord", taken from the full original phrase "anno Domini nostri Jesu Christi", which translates to "in the year of our Lord Jesus Christ".

This calendar era is based on the traditionally reckoned year of the conception or birth of Jesus of Nazareth, with AD counting years from the start of this epoch, and BC denoting years before the start of the era. There is no year zero in this scheme, so the year AD 1 immediately follows the year 1 BC. This dating system was devised in 525 by Dionysius Exiguus of Scythia Minor, but was not widely used until after 800.The Gregorian calendar is the most widely used calendar in the world today. For decades, it has been the unofficial global standard, adopted in the pragmatic interests of international communication, transportation, and commercial integration, and recognized by international institutions such as the United Nations.Traditionally, English followed Latin usage by placing the "AD" abbreviation before the year number. However, BC is placed after the year number (for example: AD 2019, but 68 BC), which also preserves syntactic order. The abbreviation is also widely used after the number of a century or millennium, as in "fourth century AD" or "second millennium AD" (although conservative usage formerly rejected such expressions). Because BC is the English abbreviation for Before Christ, it is sometimes incorrectly concluded that AD means After Death, i.e., after the death of Jesus. However, this would mean that the approximate 33 years commonly associated with the life of Jesus would neither be included in the BC nor the AD time scales.Terminology that is viewed by some as being more neutral and inclusive of non-Christian people is to call this the Current or Common Era (abbreviated as CE), with the preceding years referred to as Before the Common or Current Era (BCE). Astronomical year numbering and ISO 8601 avoid words or abbreviations related to Christianity, but use the same numbers for AD years.

Bengali calendars

The Bengali Calendar or Bangla Calendar (Bengali: বঙ্গাব্দ, lit. 'Baṅgābda') is a luni-solar calendar used in the Bengal region of the Indian subcontinent. A revised version of the calendar is the national and official calendar in Bangladesh and an earlier version of the calendar is followed in the Indian states of West Bengal, Tripura and Assam. The New Year in the Bengali calendar is known as Pohela Boishakh.

The Bengali era is called Bengali Sambat (BS) or the Bengali year (বাংলা সন Bangla Sôn, বাংলা সাল Bangla sal, or Bangabda) has a zero year that starts in 593/594 CE. It is 594 less than the AD or CE year in the Gregorian calendar if it is before Pôhela Bôishakh, or 593 less if after Pôhela Bôishakh.

The revised version of the Bengali calendar was officially adopted in Bangladesh in 1987. Among the Bengali community in India, the traditional Bengali Hindu calendar continues to be in use, and it sets the Hindu festivals.

Calendar of saints

The calendar of saints is a traditional Christian method of organizing a liturgical year by associating each day with one or more saints and referring to the day as the feast day or feast of said saint. The word "feast" in this context does not mean "a large meal, typically a celebratory one", but instead "an annual religious celebration, a day dedicated to a particular saint".The system arose from the early Christian custom of commemorating each martyr annually on the date of their death, or birth into heaven, a date therefore referred to in Latin as the martyr's dies natalis ("day of birth"). In the Eastern Orthodox Church, a calendar of saints is called a Menologion. "Menologion" may also mean a set of icons on which saints are depicted in the order of the dates of their feasts, often made in two panels.

Chinese calendar

The traditional China calendar (officially known as the Rural Calendar [農曆; 农历; Nónglì; 'farming calendar']), or Former Calendar (舊曆; 旧历; Jiùlì), Traditional Calendar (老曆; 老历; Lǎolì) or Lunar Calendar (陰曆; 阴历; Yīnlì; 'yin calendar'), is a lunisolar calendar which reckons years, months and days according to astronomical phenomena. It is defined by GB/T 33661-2017, "Calculation and promulgation of the Chinese calendar", issued by the Standardisation Administration of China on 12 May 2017.

Although modern day China uses the Gregorian calendar, the traditional Chinese calendar governs holidays (such as the Chinese New Year) in China and in overseas Chinese communities. It lists the dates of traditional Chinese holidays and guides people in selecting auspicious days for weddings, funerals, moving, or starting a business.

Like Chinese characters, variants of this calendar are used in different parts of the Chinese cultural sphere. Korea, Vietnam, and the Ryukyu Islands adopted the calendar, and it evolved into Korean, Vietnamese, and Ryukyuan calendars. The main difference from the traditional Chinese calendar is the use of different meridians, which leads to some astronomical events—and calendar events based on them—falling on different dates. The traditional Japanese calendar also derived from the Chinese calendar (based on a Japanese meridian), but its official use in Japan was abolished in 1873 as part of reforms after the Meiji Restoration. Calendars in Mongolia and Tibet have absorbed elements of the traditional Chinese calendar, but are not direct descendants of it.Days begin and end at midnight, and months begin on the day of the new moon. Years begin on the second (or third) new moon after the winter solstice. Solar terms govern the beginning and end of each month. Written versions in ancient China included stems and branches of the year and the names of each month, including leap months as needed. Characters indicated whether a month was long (大, 30 days) or short (小, 29 days); stem branches for the first, eleventh, and 21st days, and the date, stem branch and time of the solar terms.

Common Era

Common Era or Current Era (CE) is one of the notation systems for the world's most widely used calendar era. BCE (Before the Common Era or Before the Current Era) is the era before CE. BCE and CE are alternatives to the Dionysian BC and AD system respectively. The Dionysian era distinguishes eras using AD (anno Domini, "[the] year of [the] Lord") and BC ("before Christ"). Since the two notation systems are numerically equivalent, "2019 CE" corresponds to "AD 2019" and "400 BCE" corresponds to "400 BC". Both notations refer to the Gregorian calendar (and its predecessor, the Julian calendar). The year-numbering system utilized by the Gregorian calendar is used throughout the world today, and is an international standard for civil calendars.The expression has been traced back to 1615, when it first appeared in a book by Johannes Kepler as the Latin usage annus aerae nostrae vulgaris, and to 1635 in English as "Vulgar Era". The term "Common Era" can be found in English as early as 1708, and became more widely used in the mid-19th century by Jewish religious scholars. In the later 20th century, the use of CE and BCE was popularized in academic and scientific publications, and more generally by authors and publishers wishing to emphasize sensitivity to non-Christians, by not explicitly referencing Jesus as "Christ" and Dominus ("Lord") through use of the abbreviation "AD".


Easter, also called Pascha (Greek, Latin) or Resurrection Sunday, is a festival and holiday commemorating the resurrection of Jesus from the dead, described in the New Testament as having occurred on the third day after his burial following his crucifixion by the Romans at Calvary c. 30 AD. It is the culmination of the Passion of Jesus, preceded by Lent (or Great Lent), a 40-day period of fasting, prayer, and penance.

Most Christians refer to the week before Easter as "Holy Week", which contains the days of the Easter Triduum, including Maundy Thursday, commemorating the Maundy and Last Supper, as well as Good Friday, commemorating the crucifixion and death of Jesus. In Western Christianity, Eastertide, or the Easter Season, begins on Easter Sunday and lasts seven weeks, ending with the coming of the 50th day, Pentecost Sunday. In Eastern Christianity, the season of Pascha begins on Pascha and ends with the coming of the 40th day, the Feast of the Ascension.

Easter and the holidays that are related to it are moveable feasts which do not fall on a fixed date in the Gregorian or Julian calendars which follow only the cycle of the Sun; rather, its date is offset from the date of Passover and is therefore calculated based on a lunisolar calendar similar to the Hebrew calendar. The First Council of Nicaea (325) established two rules, independence of the Jewish calendar and worldwide uniformity, which were the only rules for Easter explicitly laid down by the council. No details for the computation were specified; these were worked out in practice, a process that took centuries and generated a number of controversies. It has come to be the first Sunday after the ecclesiastical full moon that occurs on or soonest after 21 March, but calculations vary.

Easter is linked to the Jewish Passover by much of its symbolism, as well as by its position in the calendar. In most European languages the feast is called by the words for passover in those languages; and in the older English versions of the Bible the term Easter was the term used to translate passover. Easter customs vary across the Christian world, and include sunrise services, exclaiming the Paschal greeting, clipping the church, and decorating Easter eggs (symbols of the empty tomb). The Easter lily, a symbol of the resurrection, traditionally decorates the chancel area of churches on this day and for the rest of Eastertide. Additional customs that have become associated with Easter and are observed by both Christians and some non-Christians include egg hunting, the Easter Bunny, and Easter parades. There are also various traditional Easter foods that vary regionally.

Fiscal year

A fiscal year (or financial year, or sometimes budget year) is the period used by governments for accounting and budget purposes, which varies between countries. It is also used for financial reporting by business and other organizations. Laws in many jurisdictions require company financial reports to be prepared and published on an annual basis, but generally do not require the reporting period to align with the calendar year (1 January to 31 December). Taxation laws generally require accounting records to be maintained and taxes calculated on an annual basis, which usually corresponds to the fiscal year used for government purposes. The calculation of tax on an annual basis is especially relevant for direct taxation, such as income tax. Many annual government fees—such as Council rates, licence fees, etc.—are also levied on a fiscal year basis, while others are charged on an anniversary basis.

The "fiscal year end" (FYE) is the date that marks the end of the fiscal year. Some companies—such as Cisco Systems—end their fiscal year on the same day of the week each year, e.g. the day that is closest to a particular date (for example, the Friday closest to 31 December). Under such a system, some fiscal years will have 52 weeks and others 53 weeks.

The calendar year is used as the fiscal year by about 65% of publicly traded companies in the United States and for a majority of large corporations in the UK and elsewhere, with notable exceptions being in Australia, New Zealand and Japan.Many universities have a fiscal year which ends during the summer to align the fiscal year with the academic year (and, in some cases involving public universities, with the state government's fiscal year), and because the university is normally less busy during the summer months. In the northern hemisphere this is July to the next June. In the southern hemisphere this is calendar year, January to December. Some media/communication-based organizations use a broadcast calendar as the basis for their fiscal year.

The fiscal year is usually denoted by the calendar year in which it ends, so United States federal government spending incurred on 14 November 2019 would belong to fiscal year 2020, operating on a fiscal calendar of October–September.

Gregorian calendar

The Gregorian calendar is the calendar used in most of the world. It is named after Pope Gregory XIII, who introduced it in October 1582. The calendar spaces leap years to make the average year 365.2425 days long, approximating the 365.2422-day tropical year that is determined by the Earth's revolution around the Sun. The rule for leap years is:

Every year that is exactly divisible by four is a leap year, except for years that are exactly divisible by 100, but these centurial years are leap years if they are exactly divisible by 400. For example, the years 1700, 1800, and 1900 are not leap years, but the year 2000 is.

The calendar was developed as a correction to the Julian calendar, shortening the average year by 0.0075 days to stop the drift of the calendar with respect to the equinoxes. To deal with the 10 days' difference (between calendar and reality) that this drift had already reached, the date was advanced so that 4 October 1582 was followed by 15 October 1582. There was no discontinuity in the cycle of weekdays or of the Anno Domini calendar era. The reform also altered the lunar cycle used by the Church to calculate the date for Easter (computus), restoring it to the time of the year as originally celebrated by the early Church.

The reform was adopted initially by the Catholic countries of Europe and their overseas possessions. Over the next three centuries, the Protestant and Eastern Orthodox countries also moved to what they called the Improved calendar, with Greece being the last European country to adopt the calendar in 1923. To unambiguously specify a date during the transition period, (or in history texts), dual dating is sometimes used to specify both Old Style and New Style dates (abbreviated as O.S and N.S. respectively). Due to globalization in the 20th century, the calendar has also been adopted by most non-Western countries for civil purposes. The calendar era carries the alternative secular name of "Common Era".

Hebrew calendar

The Hebrew or Jewish calendar (הַלּוּחַ הָעִבְרִי, Ha-Luah ha-Ivri) 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 readings, among many ceremonial uses. In Israel, it is used for religious purposes, provides a time frame for agriculture and is an official calendar for civil purposes, although the latter usage has been steadily declining in favor of the Gregorian calendar.

The present Hebrew calendar is the product of evolution, including a Babylonian influence. Until the Tannaitic period (approximately 10–220 CE), the calendar employed a new crescent moon, with an additional month normally added every two or three years to correct for the difference between twelve lunar months and the solar year. The year in which it was added was based on observation of natural agriculture-related events in ancient Israel. Through the Amoraic period (200–500 CE) and into the Geonic period, this system was gradually displaced by the mathematical rules used today. The principles and rules were fully codified by Maimonides in the Mishneh Torah in the 12th century. Maimonides' work also replaced counting "years since the destruction of the Temple" with the modern creation-era Anno Mundi.

The Hebrew lunar year is about eleven days shorter than the solar year and uses the 19-year Metonic cycle to bring it into line with the solar year, with the addition of an intercalary month every two or three years, for a total of seven times per 19 years. Even with this intercalation, the average Hebrew calendar year is longer by about 6 minutes and 40 seconds than the current mean tropical year, so that every 217 years the Hebrew calendar will fall a day behind the current mean tropical year; and about every 238 years it will fall a day behind the mean Gregorian calendar year.The era used since the Middle Ages is the Anno Mundi epoch (Latin for "in the year of the world"; Hebrew: לבריאת העולם‎, "from the creation of the world"). As with Anno Domini (A.D. or AD), the words or abbreviation for Anno Mundi (A.M. or AM) for the era should properly precede the date rather than follow it.

AM 5779 began at sunset on 9 September 2018 and will end at sunset on 29 September 2019.

Hindu calendar

Hindu calendar is a collective term for the various lunisolar calendars traditionally used in the Indian subcontinent. They adopt a similar underlying concept for timekeeping, but differ in their relative emphasis to moon cycle or the sun cycle and the names of months and when they consider the New Year to start. Of the various regional calendars, the most studied and known Hindu calendars are the Shalivahana Shaka found in South India, Vikram Samvat (Bikrami) found in North and Central regions of India, Tamil calendar used in Tamil Nadu, and the Bengali calendar used in the Bengal – all of which emphasize the lunar cycle. Their new year starts in spring. In contrast, in regions such as Kerala, the solar cycle is emphasized and this is called the Malayalam calendar, their new year starts in autumn, and these have origins in the second half of the 1st millennium CE. A Hindu calendar is sometimes referred to as Panchanga (पञ्चाङ्ग).The ancient Hindu calendar conceptual design is also found in the Jewish calendar, but different from the Gregorian calendar. Unlike Gregorian calendar which adds additional days to lunar month to adjust for the mismatch between twelve lunar cycles (354 lunar days) and nearly 365 solar days, the Hindu calendar maintains the integrity of the lunar month, but insert an extra full month by complex rules, every few years, to ensure that the festivals and crop-related rituals fall in the appropriate season.The Hindu calendars have been in use in the Indian subcontinent since ancient times, and remains in use by the Hindus in India and Nepal particularly to set the Hindu festival dates such as Holi, Maha Shivaratri, Vaisakhi, Raksha Bandhan, Pongal, Onam, Krishna Janmashtami, Durga Puja, Ram Navami, Pana Sankranti, Vishu and Diwali. Early Buddhist communities of India adopted the ancient Indian calendar, later Vikrami calendar and then local Buddhist calendars. Buddhist festivals continue to be scheduled according to a lunar system. The Buddhist calendar and the traditional lunisolar calendars of Cambodia, Laos, Myanmar, Sri Lanka and Thailand are also based on an older version of the Hindu calendar. Similarly, the ancient Jain traditions have followed the same lunisolar system as the Hindu calendar for festivals, texts and inscriptions. However, the Buddhist and Jain timekeeping systems have attempted to use the Buddha and the Mahavira's lifetimes as their reference points.The Hindu calendar is also important to the practice of Hindu astrology and zodiac system.

ISO 8601

ISO 8601 Data elements and interchange formats – Information interchange – Representation of dates and times is an international standard covering the exchange of date- and time-related data. It was issued by the International Organization for Standardization (ISO) and was first published in 1988. The purpose of this standard is to provide an unambiguous and well-defined method of representing dates and times, so as to avoid misinterpretation of numeric representations of dates and times, particularly when data are transferred between countries with different conventions for writing numeric dates and times.

In general, ISO 8601 applies to representations and formats of dates in the Gregorian (and potentially proleptic Gregorian) calendar, of times based on the 24-hour timekeeping system (with optional UTC offset), of time intervals, and combinations thereof. The standard does not assign any specific meaning to elements of the date/time to be represented; the meaning will depend on the context of its use. In addition, dates and times to be represented cannot include words with no specified numerical meaning in the standard (e.g., names of years in the Chinese calendar) or that do not use characters (e.g., images, sounds).In representations for interchange, dates and times are arranged so the largest temporal term (the year) is placed to the left and each successively smaller term is placed to the right of the previous term. Representations must be written in a combination of Arabic numerals and certain characters (such as "-", ":", "T", "W", and "Z") that are given specific meanings within the standard; the implication is that some commonplace ways of writing parts of dates, such as "January" or "Thursday", are not allowed in interchange representations.

Islamic calendar

The Islamic, Muslim, or Hijri calendar (Arabic: التقويم الهجري‎ at-taqwīm al-hijrī) is a lunar calendar consisting of 12 lunar months in a year of 354 or 355 days. It is used to determine the proper days of Islamic holidays and rituals, such as the annual period of fasting and the proper time for the pilgrimage to Mecca. The civil calendar of almost all countries where the religion is predominantly Muslim is the Gregorian calendar. Notable exceptions to this rule are Iran and Afghanistan, which use the Solar Hijri calendar. Rents, wages and similar regular commitments are generally paid by the civil calendar.The Islamic calendar employs the Hijri era whose epoch was established as the Islamic New Year of 622 AD/CE. During that year, Muhammad and his followers migrated from Mecca to Yathrib (now Medina) and established the first Muslim community (ummah), an event commemorated as the Hijra. In the West, dates in this era are usually denoted AH (Latin: Anno Hegirae, "in the year of the Hijra") in parallel with the Christian (AD), Common (CE) and Jewish eras (AM). In Muslim countries, it is also sometimes denoted as H from its Arabic form (سَنة هِجْريّة, abbreviated هـ). In English, years prior to the Hijra are reckoned as BH ("Before the Hijra").The current Islamic year is 1440 AH. In the Gregorian calendar, 1440 AH runs from approximately 11 September 2018 to 30 August 2019.

Julian calendar

The Julian calendar, proposed by Julius Caesar in 46 BC (708 AUC), was a reform of the Roman calendar. It took effect on 1 January 45 BC (709 AUC), by edict. It was the predominant calendar in the Roman world, most of Europe, and in European settlements in the Americas and elsewhere, until it was refined and gradually replaced by the Gregorian calendar, promulgated in 1582 by Pope Gregory XIII.

The Julian calendar is still used in parts of the Eastern Orthodox Church, in parts of Oriental Orthodoxy and Anabaptism, as well as by the Berbers.

During the 20th and 21st centuries, the date according to the Julian calendar is 13 days behind the Gregorian date, and after the year 2100 will be one day more.


A month is a unit of time, used with calendars, which is approximately as long as a natural period related to the motion of the Moon; month and Moon are cognates. The traditional concept arose with the cycle of Moon phases; such months (lunations) are synodic months and last approximately 29.53 days. From excavated tally sticks, researchers have deduced that people counted days in relation to the Moon's phases as early as the Paleolithic age. Synodic months, based on the Moon's orbital period with respect to the Earth-Sun line, are still the basis of many calendars today, and are used to divide the year.

Old Style and New Style dates

Old Style (O.S.) and New Style (N.S.) are terms sometimes used with dates to indicate that the calendar convention used at the time described is different from that in use at the time the document was being written. There were two calendar changes in Great Britain and its colonies, which may sometimes complicate matters: the first was to change the start of the year from Lady Day (25 March) to 1 January; the second was to discard the Julian calendar in favour of the Gregorian calendar. Closely related is the custom of dual dating, where writers gave two consecutive years to reflect differences in the starting date of the year, or to include both the Julian and Gregorian dates.

Beginning in 1582, the Gregorian calendar replaced the Julian in Roman Catholic countries. This change was implemented subsequently in Protestant and Orthodox countries, usually at much later dates. In England and Wales, Ireland, and the British colonies, the change to the start of the year and the changeover from the Julian calendar occurred in 1752 under the Calendar (New Style) Act 1750. In Scotland, the legal start of the year had already been moved to 1 January (in 1600), but Scotland otherwise continued to use the Julian calendar until 1752. Thus "New Style" can either refer to the start of year adjustment, or to the adoption of the Gregorian calendar.

In Russia, new style dates came into use in early 1918. Other countries in Eastern Orthodoxy adopted new style dating for their civil calendars but most continue to use the Julian calendar for religious use. In English-language histories of other countries (especially Russia), the Anglophone OS/NS convention is often used to identify which calendar is being used when giving a date. is a web-based suite of webmail, contacts, tasks, and calendaring services from Microsoft. One of the world's first webmail services, it was founded in 1996 as Hotmail (stylized as HoTMaiL) by Sabeer Bhatia and Jack Smith in Mountain View, California, and headquartered in Sunnyvale. Microsoft acquired Hotmail in 1997 for an estimated $400 million and launched it as MSN Hotmail, later rebranded to Windows Live Hotmail as part of the Windows Live suite of products. Microsoft released the final version of Hotmail in October 2011 and it was replaced by in 2013.

Pahela Baishakh

Pahela Baishakh (Bengali: পহেলা বৈশাখ, meaning: first of Baishakh) or Bangla Noboborsho (Bengali: বাংলা নববর্ষ, meaning: Bengali New Year) is the first day of Bengali calendar. It is celebrated on 14 April as a national holiday in Bangladesh and on 14 or 15 April in the Indian states of West Bengal, Tripura and parts of Assam and Odisha by people of Bengali heritage, irrespective of their religious faith.The festival date is set according to the solar Bengali calendar as the first day of its first month Baishakh. It therefore almost always falls on or about 14 April every year on the Gregorian calendar. The same day is observed elsewhere as the traditional solar new year and a harvest festival by Hindus and Sikhs, and is known by other names such as Vaisakhi in central and north India, Vishu in Kerala and Puthandu in Tamil Nadu.The festival is celebrated with processions, fairs and family time. The traditional greeting is "Shubho Noboborsho" (শুভ নববর্ষ, lit. "Happy New Year"). The festive Mangal Shobhajatra is organized in Bangladesh since 1989. In 2016, the UNESCO declared this festivity organized by the Faculty of Fine Arts, University of Dhaka as a cultural heritage of humanity.

Vikram Samvat

Vikram Samvat (IAST: Vikrama Samvat) (abbreviated as V.S. (or VS) or B.S. (or BS)); Listen ) (also called the Vikrami calendar) is the historical Hindu calendar from the Indian subcontinent and the official calendar of modern-day India and Nepal. It uses lunar months and solar sidereal years.


A year is the orbital period of the Earth moving in its orbit around the Sun. Due to the Earth's axial tilt, the course of a year sees the passing of the seasons, marked by change in weather, the hours of daylight, and, consequently, vegetation and soil fertility. The current year is 2019.

In temperate and subpolar regions around the planet, four seasons are generally recognized: spring, summer, autumn, and winter. In tropical and subtropical regions, several geographical sectors do not present defined seasons; but in the seasonal tropics, the annual wet and dry seasons are recognized and tracked.

A calendar year is an approximation of the number of days of the Earth's orbital period as counted in a given calendar. The Gregorian calendar, or modern calendar, presents its calendar year to be either a common year of 365 days or a leap year of 366 days, as do the Julian calendars; see below. For the Gregorian calendar, the average length of the calendar year (the mean year) across the complete leap cycle of 400 years is 365.2425 days. The ISO standard ISO 80000-3, Annex C, supports the symbol a (for Latin annus) to represent a year of either 365 or 366 days. In English, the abbreviations y and yr are commonly used.

In astronomy, the Julian year is a unit of time; it is defined as 365.25 days of exactly 86,400 seconds (SI base unit), totalling exactly 31,557,600 seconds in the Julian astronomical year.The word year is also used for periods loosely associated with, but not identical to, the calendar or astronomical year, such as the seasonal year, the fiscal year, the academic year, etc. Similarly, year can mean the orbital period of any planet; for example, a Martian year and a Venusian year are examples of the time a planet takes to transit one complete orbit. The term can also be used in reference to any long period or cycle, such as the Great Year.

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