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50-610: The Iran International Exhibitions Company (IIEC) oversees and operates all international and specialized exhibitions held in Iran. Site features exhibitions calendar and provides trade laws and regulations. IIEC is affiliated with the Ministry of Industry, Mine and Trade . IIEC is located at the Tehran permanent fairground. This Iran -related article is a stub . You can help Misplaced Pages by expanding it . This Asian corporation or company article

100-415: 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, synchronized 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 synchronized with

150-545: 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. Intercalary month The solar or tropical year does not have

200-548: A calendar based on the reign of their current sovereign. For example, the year 2006 in Japan is year 18 Heisei, with Heisei being the era name of Emperor Akihito . 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

250-437: 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

300-435: 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 as part of

350-417: 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 the lunar phase. The Gregorian calendar is the de facto international standard and is used almost everywhere in the world for civil purposes. The widely used solar aspect is a cycle of leap days in a 400-year cycle designed to keep

400-484: 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

450-423: A given year may be determined using regular cycles such as the 19-year Metonic cycle ( Hebrew calendar and in the determination of Easter ) or using calculations of lunar phases ( Hindu lunisolar and Chinese calendars ). The Buddhist calendar adds both an intercalary day and month on a usually regular cycle. In principle, lunar calendars do not employ intercalation because they do not seek to synchronise with

500-534: 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. A lunisolar calendar is a lunar calendar that compensates by adding an extra month as needed to realign the months with the seasons. Prominent examples of lunisolar calendar are Hindu calendar and Buddhist calendar that are popular in South Asia and Southeast Asia . Another example

550-412: A matter of addition and subtraction. Other calendars have one (or multiple) larger units of time. Calendars that contain one level of cycles: Calendars with two levels of cycles: Cycles can be synchronized with periodic phenomena: 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,

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600-513: A sixth epagomenal day is intercalated every four years in some (Coptic, Ethiopian and French Republican calendars). The Solar Hijri calendar , used in Iran, is based on solar calculations and is similar to the Gregorian calendar in its structure, and hence the intercalation, with the exception that its epoch is the Hijrah . The Bahá'í calendar includes enough epagomenal days (usually 4 or 5) before

650-486: A whole number of days (it is about 365.24 days), but a calendar year must have a whole number of days. The most common way to reconcile the two is to vary the number of days in the calendar year. In solar calendars, this is done by adding an extra day ("leap day" or "intercalary day") to a common year of 365 days, about once every four years, creating a leap year that has 366 days ( Julian , Gregorian and Indian national calendars ). The Decree of Canopus , issued by

700-510: 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

750-429: Is a stub . You can help Misplaced Pages by expanding it . Calendar A calendar is a system of organizing days . This is done by giving names to periods of time , typically days, weeks , months and years . A date is the designation of a single and 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

800-604: Is based on the prohibition of intercalation ( nasi' ) by Muhammad , in Islamic tradition dated to a sermon given 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. There have been several modern proposals for reform of the modern calendar, such as the World Calendar , the International Fixed Calendar ,

850-470: 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. Historically, several countries have based their calendars on regnal years ,

900-471: 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. The early Roman calendar , created during the reign of Romulus , lumped

950-672: Is repeated approximately every 33 Islamic years. Various Hindu calendars remain in use in the Indian subcontinent, including the Nepali calendars , 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

1000-459: Is the Hebrew calendar, which uses a 19-year cycle . 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

1050-612: Is used in Iran and some parts of Afghanistan . The Assyrian calendar is in use by the members of the Assyrian community in the Middle East (mainly Iraq, Syria, Turkey, and Iran) and the diaspora. The first year of the calendar is exactly 4750 years prior to the start of the Gregorian calendar. The Ethiopian calendar or Ethiopic calendar is the principal calendar used in Ethiopia and Eritrea , with

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1100-416: Is usually no discernible order in the sequencing of 29- or 30-day month lengths. Traditionally, the first day of each month is the day (beginning at sunset) of the first sighting of the hilal (crescent moon) shortly after sunset. If the hilal is not observed immediately after the 29th day of a month (either because clouds block its view or because the western sky is still too bright when the moon sets), then

1150-514: The Hellenistic period they gave rise to the ancient Roman calendar and to various Hindu calendars . 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

1200-525: The Holocene calendar , and 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 and the massive upheaval that implementing them would involve, as well as their effect on cycles of religious activity. A full calendar system has a different calendar date for every day. Thus the week cycle is by itself not

1250-554: 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 . A fiscal calendar generally means the accounting year of a government or

1300-469: The solar year over the long term. The term calendar is taken from kalendae , 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. Latin calendarium meant 'account book, register' (as accounts were settled and debts were collected on the calends of each month). The Latin term

1350-530: The 61 days of the winter period them together as simply "winter." Over time, this period became January and February; through further changes over time (including the creation of the Julian calendar ) this calendar became the modern Gregorian calendar, introduced in the 1570s. 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,

1400-723: 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 business dealings (such as for

1450-494: The Julian calendar this was done every four years. In the Gregorian, years divisible by 100 but not 400 were exempted in order to improve accuracy. Thus, 2000 was a leap year; 1700, 1800, and 1900 were not. Epagomenal days are days within a solar calendar that are outside any regular month. Usually five epagomenal days are included within every year ( Egyptian , Coptic , Ethiopian , Mayan Haab' and French Republican Calendars ), but

1500-582: The Old Calendar) and the Revised Julian Calendar (often called the New Calendar). The Revised Julian Calendar is nearly the same as the Gregorian calendar, with the addition that years divisible by 100 are not leap years , except that years with remainders of 200 or 600 when divided by 900 remain leap years, e.g. 2000 and 2400 as in the Gregorian calendar. The Islamic calendar or Hijri calendar

1550-533: The Roman Rite of the Catholic Church, and generally include the liturgical seasons of Advent , Christmas , Ordinary Time (Time after Epiphany ), Lent , Easter , and Ordinary Time (Time after Pentecost ). Some Christian calendars do not include Ordinary Time and every day falls into a denominated season. The Eastern Orthodox Church employs the use of 2 liturgical calendars; the Julian calendar (often called

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1600-574: The Roman calendar contained remnants of a very ancient pre-Etruscan 10-month solar year. The first recorded physical calendars, dependent on the development of writing in the Ancient Near East , are the Bronze Age Egyptian and Sumerian calendars. During the Vedic period India developed a sophisticated timekeeping methodology and calendars for Vedic rituals. According to Yukio Ohashi,

1650-978: The Vedanga calendar in ancient India was based on astronomical studies during the Vedic Period and was not derived from other cultures. A large number of calendar systems in the Ancient Near East were based on the Babylonian calendar dating 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 . A great number of Hellenic calendars were developed in Classical Greece , and during

1700-483: The annual flooding of the Nile River. They built a calendar with 365 days, divided into 12 months of 30 days each, with 5 extra days at the end of the year. However, they did not include the extra bit of time in each year, and this caused their calendar to slowly become inaccurate. 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

1750-697: The dating of cheques ). Followers of the Baháʼí Faith use the Baháʼí calendar . The Baháʼí Calendar, also known as the Badi Calendar was first established by the Bab in the Kitab-i-Asma. The Baháʼí Calendar is also purely a solar calendar and comprises 19 months each having nineteen days. The Chinese , Hebrew , Hindu , and Julian calendars are widely used for religious and social purposes. The Iranian (Persian) calendar

1800-456: The day that begins at that sunset is the 30th. The tabular Islamic calendar , used in Iran, has 12 lunar months that usually alternate between 30 and 29 days every year, but an intercalary day is added to the last month of the year 12 times in a 33-year cycle. Some historians also linked the pre-Islamic practice of Nasi' to intercalation. The International Earth Rotation and Reference Systems Service can insert or remove leap seconds from

1850-418: The duration of the year aligned with the solar year . There is a lunar aspect which approximates the position of the moon during the year, and is used in the calculation of the date of Easter . 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). The Gregorian calendar

1900-460: 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. The Egyptians appear to have been the first to develop a solar calendar, using as a fixed point the annual sunrise reappearance of the Dog Star— Sirius , or Sothis—in the eastern sky, which coincided with

1950-467: The last day of any month (June and December are preferred). These are sometimes described as intercalary. ISO 8601 includes a specification for a 52/53-week year. Any year that has 53 Thursdays has 53 weeks; this extra week may be regarded as intercalary. The xiuhpōhualli (year count) system of the Aztec calendar had five intercalary days after the eighteenth and final month, the nēmontēmi , in which

2000-598: The last month ( علاء , ʿalāʾ ) to ensure that the following year starts on the March equinox . These are known as the Ayyám-i-Há . The solar year does not have a whole number of lunar months (it is about 365/29.5 = 12.37 lunations ), so a lunisolar calendar must have a variable number of months per year. Regular years have 12 months, but embolismic years insert a 13th "intercalary" or "leap" month or "embolismic" month every second or third year. Whether to insert an intercalary month in

2050-488: 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, believed that marks on a bone baton ( c.  25,000 BC ) represented

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2100-424: 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

2150-450: The observation of religious feast days. While the Gregorian calendar is itself historically motivated 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 several calendars in use for religious purposes. Western Christian liturgical calendars are based on the cycle of

2200-516: The pharaoh Ptolemy III Euergetes of Ancient Egypt in 239 BC, decreed a solar leap day system; an Egyptian leap year was not adopted until 25 BC, when the Roman Emperor Augustus instituted a reformed Alexandrian calendar . In the Julian calendar , as well as in the Gregorian calendar , which improved upon it, intercalation is done by adding an extra day to February in each leap year. In

2250-412: The seasons, and the motion of the moon is astronomically predictable. But religious lunar calendars rely on actual observation. The Lunar Hijri calendar , the purely lunar calendar observed by most of Islam, depends on actual observation of the first crescent of the moon and thus has no intercalation. Each month still has either 29 or 30 days, but due to the variable method of observations employed, there

2300-414: 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. 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

2350-399: 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 Christian Era ). The most important use of pre-modern calendars is keeping track of the liturgical year and

2400-610: 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). The course of the Sun and the Moon are the most salient regularly recurring natural events useful for timekeeping , and in pre-modern societies around the world lunation and the year were most commonly used as time units. Nevertheless,

2450-539: Was introduced in 1582 as a refinement to the Julian calendar , that 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, its adoption was mostly limited to Roman Catholic nations, but by the 19th century it had become widely adopted for the sake of convenience in international trade. The last European country to adopt it

2500-429: Was reformed by Julius Caesar in 46 BC. His "Julian" calendar was no longer dependent on the observation of the new moon, but followed an algorithm of introducing a leap day every four years. This created a dissociation of the calendar month from lunation . The Gregorian calendar , introduced in 1582, corrected most of the remaining difference between the Julian calendar and the solar year. The Islamic calendar

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