A page from the Hindu calendar 1871–1872.

A calendar is a system of organizing days for a social, religious, commercial or administrative purpose. This organization 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 cycles of some astronomical phenomenon, such as the cycle of the sun, or the moon. A calendar marks the days of the year. ... Image File history File links Size of this preview: 221 × 598 pixelsFull resolution (640 × 1731 pixel, file size: 307 KB, MIME type: image/jpeg) Faithful reproductions of two-dimensional original works cannot attract copyright in the U.S. according to the rule in Bridgeman Art Library v. ... Image File history File links Size of this preview: 221 × 598 pixelsFull resolution (640 × 1731 pixel, file size: 307 KB, MIME type: image/jpeg) Faithful reproductions of two-dimensional original works cannot attract copyright in the U.S. according to the rule in Bridgeman Art Library v. ... A page from the Hindu calendar 1871-72. ... This article is about the concept of time. ... Look up day in Wiktionary, the free dictionary. ... For more details on each day of the week, see days of the week. ... Look up Month in Wiktionary, the free dictionary. ... A year (from Old English gÄ“r) is the time between two recurrences of an event related to the orbit of the Earth around the Sun. ... A date in a calendar is a reference to a particular day represented within a calendar system. ... Astronomy, which etymologically means law of the stars, (from Greek: αστρονομία = άστρον + νόμος) is a science involving the observation and explanation of events occurring outside Earth and its atmosphere. ...

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.

As a subset, 'calendar' is also used to denote a list of particular set of planned events (for example, court calendar).

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. For more details on each day of the week, see days of the week. ... A year (from Old English gēr) is the time between two recurrences of an event related to the orbit of the Earth around the Sun. ...

The simplest calendar system just counts days from a reference day. This applies for the Julian day. Virtually the only possible variation is using a different reference day, 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. “JDN” redirects here. ...

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: ISO 8601 is an international standard for date and time representations issued by the International Organization for Standardization (ISO). ...

• year, month, and day – most systems, including the Gregorian calendar (and its very similar predecessor, the Julian calendar), the Islamic calendar, and the Hebrew calendar
• year, week, and weekday – e.g. the ISO week date

Cycles can be synchronized with periodic phenomena: Look up Month in Wiktionary, the free dictionary. ... For the calendar of religious holidays and periods, see liturgical year. ... The Julian calendar was a reform of the Roman calendar which was introduced by Julius Caesar in 46 BC and came into force in 45 BC (709 ab urbe condita). ... The Islamic calendar or Muslim calendar (Arabic: التقويم الهجري; at-taqwīm al-hijrī; Persian: تقویم هجري قمری ‎ taqwīm-e hejri-ye qamari; also called the Hijri calendar) is the calendar used to date events in many predominantly Muslim countries, and used by Muslims everywhere to determine the proper day on which to celebrate... The Hebrew calendar (‎) or Jewish calendar is a lunisolar calendar used by Jews for predominantly religious purposes. ... The ISO week date system is a leap week calendar system that is part of the ISO 8601 date and time standard. ...

• A lunar calendar is synchronized to the motion of the Moon (lunar phases); an example is the Islamic calendar.
• A solar calendar is based on perceived seasonal changes synchronized to the apparent motion of the Sun; an example is the Persian calendar.
• There are some calendars that appear to be synchronized to the motion of Venus, such as some of the ancient Egyptian calendars; synchronization to Venus appears to occur primarily in civilizations near the Equator.
• The week cycle is an example of one that is not synchronized to any external phenomenon (although it may have been derived from lunar phases, beginning anew every month).

Very commonly a calendar includes more than one type of cycle, or has both cyclic and acyclic elements. A lunisolar calendar is synchronized both to the motion of the moon and to the apparent motion of the sun; an example is the Hebrew calendar. This article is about Earths moon. ... Moon phase redirects here. ... The Islamic calendar or Muslim calendar (Arabic: التقويم الهجري; at-taqwīm al-hijrī; Persian: تقویم هجري قمری ‎ taqwīm-e hejri-ye qamari; also called the Hijri calendar) is the calendar used to date events in many predominantly Muslim countries, and used by Muslims everywhere to determine the proper day on which to celebrate... The seasonal year is the time between successive recurrences of a seasonal event such as the flooding of a river, the migration of a species of bird, or the flowering of a species of plant. ... This article is in need of attention. ... For other uses, see Venus (disambiguation). ... The pyramids are the most recognizable symbols of the civilization of ancient Egypt. ... World map showing the equator in red For other uses, see Equator (disambiguation). ... For more details on each day of the week, see days of the week. ... The Hebrew calendar (‎) or Jewish calendar is a lunisolar calendar used by Jews for predominantly religious purposes. ...

Many calendars incorporate simpler calendars as elements. For example, the rules of the Hebrew calendar depend on the seven-day week cycle (a very simple calendar), so the week is one of the cycles of the Hebrew calendar. It is also common to operate two calendars simultaneously, usually providing unrelated cycles, and the result may also be considered a more complex calendar. For example, the Gregorian calendar has no inherent dependence on the seven-day week, but in Western society the two are used together, and calendar tools indicate both the Gregorian date and the day of week. For the calendar of religious holidays and periods, see liturgical year. ... Occident redirects here. ...

The week cycle is shared by various calendar systems (although the significance of special days such as Friday, Saturday, and Sunday varies). Systems of leap days usually do not affect the week cycle. The week cycle was not even interrupted when 10, 11, 12, or 13 dates were skipped when the Julian calendar was replaced by the Gregorian calendar by various countries.

Mayan Calendar

Main article: Mayan calendar

The Maya calendar is a system of complex and highly developed calendars created by the Maya Civilization of pre-Columbian Mesoamerica. ...

Solar calendars

Main article: Solar calendar

A solar calendar is a calendar whose dates indicate the position of the earth on its revolution around the sun (or equivalently the apparent position of the sun moving on the celestial sphere). ...

Days used by 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. Solar time is based on the idea that when the sun reaches its highest point in the sky, it is noon. ... A typical sunrise, in New Zealand A sunrise through clouds over Oakland, California. ... A composite image showing the terminator dividing night from day, running across Europe and Africa. ... This article is about the time of day. ... Solar time is based on the idea that when the sun reaches its highest point in the sky, it is noon. ...

Calendar reform

Main article: Calendar reform

There have been a number of proposals for reform of the calendar, such as the World Calendar, International Fixed Calendar and Holocene calendar. The United Nations considered adopting such a reformed calendar for a while in the 1950s, but these proposals have lost most of their popularity. Calendar reform is any proposed reform of a calendar. ... The World Calendar is a proposed reform of the Gregorian calendar created by Elisabeth Achelis of Brooklyn, New York in 1930. ... The International Fixed calendar (also known as the International Perpetual calendar, the Cotsworth plan, the Eastman plan, the 13 Month calendar or the Equal Month calendar) is a proposal for calendar reform providing for a year of 13 months of 28 days each, with one day at the end of... H.E. redirects here. ... UN redirects here. ...

Lunar calendars

Main article: Lunar calendar

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 don't vary much near the equator. It does, however, stay constant with respect to other phenomena, notably tides. An example is the Islamic calendar. A lunar calendar is a calendar that is based on cycles of the moon phase. ... A lunar calendar is a calendar that is based on cycles of the moon phase. ... Moon phase redirects here. ... A tropical year is the length of time that the Sun, as viewed from the Earth, takes to return to the same position along the ecliptic (its path among the stars on the celestial sphere). ... World map showing the equator in red For other uses, see Equator (disambiguation). ... This article is about tides in the Earths oceans. ... The Islamic calendar or Muslim calendar (Arabic: التقويم الهجري; at-taqwīm al-hijrī; Persian: تقویم هجري قمری ‎ taqwīm-e hejri-ye qamari; also called the Hijri calendar) is the calendar used to date events in many predominantly Muslim countries, and used by Muslims everywhere to determine the proper day on which to celebrate...

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. A lunisolar calendar is a calendar whose date indicates both the moon phase and the time of the solar year. ... The Hebrew calendar (‎) or Jewish calendar is a lunisolar calendar used by Jews for predominantly religious purposes. ...

Lunar calendars are believed to be the oldest calendars invented by mankind. Cro-Magnon people are claimed to have invented one around 32,000 BC. The Cro-Magnons (IPA: or anglicised IPA: ) form the earliest known European examples of Homo sapiens, the species to which modern humans belong. ...

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. Look up Month in Wiktionary, the free dictionary. ... A year (from Old English gēr) is the time between two recurrences of an event related to the orbit of the Earth around the Sun. ... A solar calendar is a calendar whose dates indicate the position of the earth on its revolution around the sun (or equivalently the apparent position of the sun moving on the celestial sphere). ... A tropical year is the length of time that the Sun, as viewed from the Earth, takes to return to the same position along the ecliptic (its path among the stars on the celestial sphere). ... This article or section is in need of attention from an expert on the subject. ... For more details on each day of the week, see days of 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 (29 February) 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. February 29 is a day added into a leap year of the Gregorian calendar. ... For the 1921 film starring Fatty Arbuckle, see Leap Year (film). ... Intercalation is the insertioffn of an extra day, week or month into some calendar years to make the calendar follow the seasons. ...

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. For more details on each day of the week, see days of the week. ... The Emperor , literally heavenly sovereign,[1] formerly often called the Mikado) of Japan is the countrys monarch. ... For Prince Komatsu, see Prince Komatsu Akihito. ...

See Decade, Century, Millennium For other senses of this word, see decade (disambiguation). ... A century (From the Latin cent, one hundred) is one hundred consecutive years. ... A millennium (pl. ...

Other calendar types

Arithmetic and astronomical calendars

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. A stone (2. ...

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.

Uses

The primary practical use of a calendar is to identify days: to be informed about and/or to agree on a future event and to record an event that has happened. Days may be significant for civil, religious or social reasons. For example, a calendar provides a way to determine 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. Vacation redirects here. ...

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. In economics, a business (also called firm or enterprise) is a legally recognized organizational entity designed to provide goods and/or services to consumers or corporate entities such as governments, charities or other businesses. ... A family calendar is a scheduling system used by busy families to keep track of appointments and activities for multiple family members. ...

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, written calendars are no longer an essential part of such systems, as the advent of accurate clocks has made it possible to record time independently of astronomical events. For alternate uses of time, see Time (disambiguation) or see TIME (magazine). ... This article is about the concept of time. ... For other uses, see Clock (disambiguation). ...

Currently used calendars

Calendars in widespread use today include the Gregorian calendar, which is the de facto international standard, and is used almost everywhere in the world for civil purposes, including in the People's Republic of China and India (along with the Indian national calendar). Due to the Gregorian calendar's obvious connotations of Western Christianity, non-Christians and even some Christians sometimes justify its use by replacing the traditional era notations "AD" and "BC" ("Anno Domini" and "Before Christ") with "CE" and "BCE" ("Common Era" and "Before Common Era"). The Hindu calendars are some of the most ancient calendars of the world. Eastern Christians of eastern Europe and western Asia used for a long time the Julian Calendar, that of the old Orthodox church, in countries like Russia. For over 1500 years, Westerners used the Julian Calendar also. For the calendar of religious holidays and periods, see liturgical year. ... De facto is a Latin expression that means in fact or in practice. It is commonly used as opposed to de jure (meaning by law) when referring to matters of law or governance or technique (such as standards), that are found in the common experience as created or developed without... The Indian national calendar (sometimes called Saka calendar) is the official civil calendar in use in India. ... Topics in Christianity Movements · Denominations · Other religions Ecumenism · Preaching · Prayer Music · Liturgy · Calendar Symbols · Art · Criticism Important figures Apostle Paul · Church Fathers Constantine · Athanasius · Augustine Anselm · Aquinas · Palamas · Luther Calvin · Wesley Arius · Marcion of Sinope Archbishop of Canterbury · Catholic Pope Coptic Pope · Ecumenical Patriarch Christianity Portal This box:      Western Christianity... Look up AD, ad-, and ad in Wiktionary, the free dictionary. ... BC may stand for: Before Christ (see Anno Domini) : an abbreviation used to refer to a year before the beginning of the year count that starts with the supposed year of the birth of Jesus. ... BCE redirects here. ... A page from the Hindu calendar 1871-72. ... Eastern Christianity refers collectively to the Christian traditions and churches which developed in Greece, the Balkans, the rest of Eastern Europe, Asia Minor, the Middle East, northeastern Africa and southern India over several centuries of religious antiquity. ... The Julian calendar was a reform of the Roman calendar which was introduced by Julius Caesar in 46 BC and came into force in 45 BC (709 ab urbe condita). ...

While the Gregorian calendar is widely used in Israel's business and day-to-day affairs, the Hebrew calendar, 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 checks). The Hebrew calendar (‎) or Jewish calendar is a lunisolar calendar used by Jews for predominantly religious purposes. ... Languages Historical Jewish languages Hebrew, Yiddish, Ladino, others Liturgical languages: Hebrew and Aramaic Predominant spoken languages: The vernacular language of the home nation in the Diaspora, significantly including English, Hebrew, Yiddish, and Russian Religions Judaism Related ethnic groups Arabs and other Semitic groups For the Jewish religion, see Judaism. ... Example of a Canadian cheque. ...

The Persian calendar is used in Iran and Afghanistan. The Islamic calendar is used by most non-Persian Muslims worldwide. The Chinese, Hebrew, Hindu, and Julian calendars are widely used for religious and/or social purposes. The Ethiopian calendar or Ethiopic calendar is the principal calendar used in Ethiopia and Eritrea. In Thailand, the months and days have adopted the western standard, although the years are still based on the traditional Buddhist Calendar. The Iranian calendar (Persian: ), also known as Persian calendar or (mistakenly) the Jalāli Calendar is an astronomical solar calendar currently used in Iran and Afghanistan as the main official calendar. ... The Islamic calendar or Muslim calendar (Arabic: التقويم الهجري; at-taqwīm al-hijrī; Persian: تقویم هجري قمری ‎ taqwīm-e hejri-ye qamari; also called the Hijri calendar) is the calendar used to date events in many predominantly Muslim countries, and used by Muslims everywhere to determine the proper day on which to celebrate... There is also a collection of Hadith called Sahih Muslim A Muslim (Arabic: مسلم, Persian: Mosalman or Mosalmon Urdu: مسلمان, Turkish: Müslüman, Albanian: Mysliman, Bosnian: Musliman) is an adherent of the religion of Islam. ... The Hebrew calendar (‎) or Jewish calendar is a lunisolar calendar used by Jews for predominantly religious purposes. ... A page from the Hindu calendar 1871-72. ... The Julian calendar was a reform of the Roman calendar which was introduced by Julius Caesar in 46 BC and came into force in 45 BC (709 ab urbe condita). ... The Ethiopian calendar (Amharic: የኢትዮጵያ ዘመን አቆጣጠር ), also called the Geez calendar, is the principal calendar used in Ethiopia and is also the liturgical year of Christians in Eritrea belonging to the Eritrean Orthodox Tewahdo Church, Eastern Catholic Church of Eritrea and Lutheran (Evangelical Church of Eritrea), where it is commonly known... Buddhism is a variety of teachings, sometimes described as a religion[1] or way of life that attempts to identify the causes of human suffering and offer various ways that are claimed to end, or ease suffering. ...

Even where there is a commonly used calendar such as the Gregorian calendar, alternate calendars may also be used, such as a fiscal calendar or the astronomical year numbering system^[1]. A fiscal year (or financial year or accounting reference date) is a 12-month period used for calculating annual (yearly) financial statements in businesses and other organizations. ...

Fiscal calendars

Main article: Fiscal calendar

A fiscal calendar (such as a 5/4/4 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 5 weeks (Sunday through Saturday), February has 4 weeks, March has 4 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. A fiscal year or financial year is a 12-month period used for calculating annual (yearly) financial reports in businesses and other organizations. ... ISO 8601 is an international standard for date and time representations issued by the International Organization for Standardization (ISO). ... is the 4th day of the year in the Gregorian calendar. ... For the calendar of religious holidays and periods, see liturgical year. ...

School calendars

A school calendar incorporates school dates, anniversaries, school masses and carnivals (e.g. swimming and athletic carnivals). School calendars also include many reminders for school students, staff and parents.

Gregorian Calendar with Easter Sunday

Calculating the calendar of a previous year (for the Gregorian calendar taking account of the week) is a relatively easy matter when Easter Sunday is not included on the calendar. However, calculating for Easter Sunday is difficult because the calculation requires the knowledge of the full moon cycle. Easter Sunday is on the first Sunday after the first full moon after the Vernal Equinox according to the computus. So, this makes an additional calculation necessary on top of the normal calculation for January 1st and the calculation of whether or not the year is a leap year. For the calendar of religious holidays and periods, see liturgical year. ... For more details on each day of the week, see days of the week. ... Easter (also called Pascha) is generally accounted the most important holiday of the Christian year, observed March or April each year to celebrate the Resurrection of Jesus from the dead (after his death by crucifixion; see Good Friday), which Christians believe happened at about this time of year, almost two... Illumination of Earth by Sun on the day of equinox The vernal equinox (or spring equinox) marks the beginning of astronomical spring. ... Computus (Latin for computation) is the calculation of the date of Easter in the Christian calendar. ...

There are only 14 different calendars when Easter Sunday is not involved. Each calendar is determined by the day of the week January 1st falls on and whether or not the year is a leap year. However, when Easter Sunday is included, there are 70 different calendars (two for each date of Easter).

At-A-Glance 2004-2005 calendar

Image File history File links Size of this preview: 600 × 600 pixelsFull resolution (1200 × 1200 pixels, file size: 159 KB, MIME type: image/jpeg) File historyClick on a date/time to view the file as it appeared at that time. ... Image File history File links Size of this preview: 600 × 600 pixelsFull resolution (1200 × 1200 pixels, file size: 159 KB, MIME type: image/jpeg) File historyClick on a date/time to view the file as it appeared at that time. ...

Physical calendars

A calendar is also a physical device (often paper) (for example, a desktop calendar or a wall calendar). 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. A wall calendar is a calendar intended for placement on a wall. ...

The sale of physical calendars has been restricted in some countries, and given as a monopoly to universities and national academies. Examples include the Prussian Academy of Sciences and the University of Helsinki, which had a monopoly on the sale of calendars in Finland until the 1990s. This article is about the economic term. ... For the community in Florida, see University, Florida. ... A national academy is a body, usually operating with state financial support and approval, that co-ordinates the activities of research in (nearly always) the sciences and (sometimes) other disciplines. ... The Prussian Academy of Sciences (German: ) was an academy established in Berlin on July 11, 1700. ... University of Helsinki is not to be confused with Helsinki University of Technology. ...

Calendars in computing

• Electronic calendar
• Category:Calendaring standards

Packages are available that enable users to use electronic versions of a variety of office tools such as calendar, appointment book, address book and contact list. ...

Layout

There are different layouts for calendars.

A table for each week Image File history File links No higher resolution available. ...

See also

• Calendrical calculation
• Calendar reform
• Real-Time Clock (RTC), which underlies the Calendar software on modern computers.
• Time for divisions smaller than one day

A Calendrical calculation is a calculation concerning calendar dates. ... Calendar reform is any proposed reform of a calendar. ... A real-time clock (RTC) is a computer clock (most often in the form of an integrated circuit chip) that keeps track of the current time even when the computer is turned off. ... This article is about the concept of time. ...

List of calendars

Main article: List of calendars

A Tunisian calendar showing Gregorian, Islamic and Berber dates // Afghan calendar (Afghan Calendar Project) Armenian calendar Astronomical year numbering Baháí calendar Bengali calendar Berber calendar Buddhist calendar Chinese calendar Coptic calendar Ethiopian calendar Fiscal year Germanic calendar (still in use by Ásatrúar) Gregorian calendar Hebrew calendar Hindu calendars Indian... A calendar is a system for assigning calendar dates to days. ... A Tunisian calendar showing Gregorian, Islamic and Berber dates // Afghan calendar (Afghan Calendar Project) Armenian calendar Astronomical year numbering Baháí calendar Bengali calendar Berber calendar Buddhist calendar Chinese calendar Coptic calendar Ethiopian calendar Fiscal year Germanic calendar (still in use by Ásatrúar) Gregorian calendar Hebrew calendar Hindu calendars Indian... Astronomical year numbering is based on BCE/CE (or BC/AD) year numbering, but follows normal decimal integer numbering more strictly. ... For the calendar of religious holidays and periods, see liturgical year. ... The Islamic calendar or Muslim calendar (Arabic: التقويم الهجري; at-taqwīm al-hijrī; Persian: تقویم هجري قمری ‎ taqwīm-e hejri-ye qamari; also called the Hijri calendar) is the calendar used to date events in many predominantly Muslim countries, and used by Muslims everywhere to determine the proper day on which to celebrate... The ISO week date system is a leap week calendar system that is part of the ISO 8601 date and time standard. ... A lunisolar calendar is a calendar whose date indicates both the moon phase and the time of the solar year. ... A solar calendar is a calendar whose dates indicate the position of the earth on its revolution around the sun (or equivalently the apparent position of the sun moving on the celestial sphere). ... A lunar calendar is a calendar that is based on cycles of the moon phase. ... The Assyrian calender is a lunar-based calender that begins in the year 4750 BC, marking the finishing of the first temple build by the Assyrians for the God Ashur. ... The Attic calendar is the calendar that was in use in ancient Attica, the ancestral territory of the Athenian polis. ... The sun stone also called the Aztec calendar on display at the National Museum of Anthropology in Mexico City. ... The Tonalpohualli,the day-count in English, is the 260 day sacred calendar of early Mesoamericans. ... The Xiuhpohualli was a calendar cycle constructed from a count of 365 days, used by the Aztecs and other Nahua peoples from the central Mexican region during the Postclassic period of Mesoamerican chronology. ... In the Babylonian calendar a year consisted of 12 lunar months, each beginning when a new crescent moon was first sighted low on the western horizon at sunset. ... The Baháí calendar, also called the Badí‘ calendar, used by the Baháí Faith, is a solar calendar with regular years of 365 days, and leap years of 366 days. ... The Bengali calendar (Bengali: ) or Bangla calendar is a traditional solar calendar used in Bangladesh and Indias eastern states of West Bengal, Assam and Tripura. ... The Berber calendar is the annual calendar used by Berber people in North Africa. ... Bikram Samwat (Bikram Sambat, Devnagari:बिक्रम संवत, abbreviated B.S.) is the calendar established by Indian emperor Vikramaditya. ... The Buddhist calendar is used on mainland southeast Asia in the countries of Cambodia, Laos, Thailand, and Myanmar (formerly Burma) in several related forms. ... The term Celtic calendar is used to refer to a variety of calendars used by Celtic-speaking peoples at different times in history. ... The Coptic calendar, also called the Alexandrian calendar, is used by the Coptic Orthodox Church. ... A French Revolutionary Calendar in the Historical Museum of Lausanne. ... The Hebrew calendar (‎) or Jewish calendar is a lunisolar calendar used by Jews for predominantly religious purposes. ... A page from the Hindu calendar 1871-72. ... The Javanese calendar is a calendar still in use by the Javanese people of Indonesia concurrently with two other important calendars, the Gregorian calendar and the Islamic calendar. ... The Juche Idea (also Juche Sasang or Chuche; pronounced // in Korean, approximately joo-cheh) is the official state ideology of North Korea and the political system based on it. ... The Revised Julian calendar is a calendar that was considered for adoption by the Eastern Orthodox churches at a synod in Istanbul in May 1923. ... Malayalam calendar (also known as Malayalam Era or Kollavarsham) is a solar Sidereal calendar used in the state of Kerala in South India. ... The Maya calendar is a system of distinct calendars and almanacs used by the Maya civilization of pre-Columbian Mesoamerica, and by some modern Maya communities in highland Guatemala. ... Tzolkin (in the revised Guatemala Mayan languages Academy orthography which is now preferred, formerly and commonly tzolkin) is the name bestowed by Mayanist scholars upon the version of the 260-day Mesoamerican calendar which was used by the Maya civilization of pre-Columbian Mesoamerica. ... The Maya Haab calendar is a 365-day solar calendar whose dates indicate the position of the Sun at noon relative to the zenith over the Yucatan peninsula. ... A calendar that commemorates the first year of the Republic as well as the election of Sun Yat-sen as the provisional President. ... The Nanakshahi (Punjabi: , ) calendar is a solar calendar that was adopted by the Shiromani Gurdwara Prabhandak Committee to determine the dates for important Sikh events. ... Nepal Sambat (Nepal Bhasa: नेपाल सम्बत) is a lunar calendar. ... The Pawukon is a 210 day calendar that has its origins in the Hindu religion in Bali, Indonesia. ... The Roman calendar changed its form several times in the time between the foundation of Rome and the fall of the Roman Empire. ... Page of the Soviet revolutionary calendar showing December 12, 1937 The Soviet revolutionary calendar was in use in the USSR from 1929 to 1940. ... The Tamil Calendar is followed by the Tamil speaking state of Tamil Nadu and Kerala in India, and by the Tamil population in Malaysia, Singapore & Sri Lanka. ... The Thai lunar calendar or Patitin Chantarakati (Thai: ปฏิทินจันทรคติ) was replaced by the Patitin Suriyakati (ปฎิทินสุริยคติ) Thai solar calendar in AD 1888 2431 BE for most purposes, but the Chantarakati still determines most Buddhist feast or holy days, as well as a day for the famous Loy Krathong festival. ... The Thai solar, or Suriyakati (สุริยคติ), calendar is used in traditional and official contexts in Thailand, although the Western calendar is sometimes used in business. ... The Tibetan calendar is a lunisolar calendar, that is, the Tibetan year is composed of either 12 or 13 lunar months, each beginning and ending with a new moon. ... Tết display in Ho Chi Minh City Tết Nguyên Đán (Sino-Vietnamese for Feast of the First Morning, derived from Hán nôm 節元旦), more commonly known by its shortened name Tết, is the most important holiday in Vietnam. ... By the traditional Xhosa calendar, the year began in June and ended in May, when Canopus, a large star visible in the Southern Hemisphere, signalled the time for harvesting. ... The Zoroastrian calendar is a religious calendar used by members of the Zoroastrian faith, and it is an approximation of the (tropical) solar calendar. ... Runic calendar - Norwegian - carved wood. ... The Pre-Columbian people of Mesoamerica kept track of time with calendars which had ritual and religious meaning. ... Long Count redirects here. ... In the Mesoamerican calendars, Calendar Round dates are composed by interlacing the dates of the Tzolkin 260 day period (eg the Tzolkin) with that of the 365 day period (known in the Maya language as the Haab). ... The Julian calendar was a reform of the Roman calendar which was introduced by Julius Caesar in 46 BC and came into force in 45 BC (709 ab urbe condita). ... The calendar of saints is a traditional Christian method of organising a liturgical year on the level of days by associating each day with one or more saints, and referring to the day as that saints day. ... The Eastern Orthodox liturgical calendar describes and dictates the rhythm of the life of the Eastern Orthodox Church. ... The month of October from a liturgical calendar for Abbotsbury Abbey. ... The Darian Calendar is a system of time-keeping designed to serve the needs of any possible future human settlers on the planet Mars. ... The Discordian calendar is an alternative calendar used by some adherents of Discordianism. ... A perpetual calendar is a calendar which is good for a span of many years, such as the Runic calendar. ... A wall calendar is a calendar intended for placement on a wall. ... Economic calendar is a type of calendar that is intended to inform financiers and traders about the scheduled major economic numbers (like CPI, PMI, Jobless Claims), government reports and speeches of the most influential persons of the financial world. ...

Sources

• Calendrical Calculations; Nachum Dershowitz and Edward M. Reingold; Cambridge University Press, 1997; ISBN 0-521-56474-3; Book Info; Online Calculator
• Mapping Time, the calendar and its history; E G Richards; Oxford University Press, 1998; ISBN 0-19-850413-6
• A comparative Calendar of the Iranian, Muslim Lunar, and Christian Eras for Three Thousand Years; Ahmad Birashk; Mazda Publishers, 1993; ISBN 0-939214-95-4
• The Comprehensive Hebrew Calendar; Arthur Spier; Feldheim Publishers, 1986; ISBN 0-87306-398-8
• High Days and Holidays in Iceland; Árni Björnsson; Mál og menning, 1995; ISBN 9979-3-0802-8
• Explanatory Supplement to the Astronomical Almanac; P. Kenneth Seidelmann, ed.; University Science Books, 1992; ISBN 0-935702-68-7; Chapter 12: Calendars by L. E. Doggett
• Sun, Moon, and Sothis; Lynn E. Rose; Kronos Press, 1999; ISBN 0-917994-15-9
• Dieter Schuh (1973). Untersuchungen zur Geschichte der Tibetischen Kalenderrechnung. Wiesbaden: Franz Steiner Verlag GMBH. OCLC 1150484. 

Edward M. Reingold is a computer scientist active in the fields of algorithms, data structures and calendrical calculations. ... The Online Computer Library Center (OCLC) was founded in 1967 and originally named the Ohio College Library Center. ...

References

External links

Look up calendar in Wiktionary, the free dictionary.

Wikisource has the text of the 1911 Encyclopædia Britannica article Calendar.

v • d • e   Time   Major concepts Time · Eternity · Arguments for eternity · Immortality Deep time · History · Past · Present · Future · Futurology Time Portal Measurement and Standards Chronometry · UTC · UT · TAI · Second · Minute · Hour · Sidereal time · Solar time · Time zone Clock · Horology · History of timekeeping devices · Astrarium · Marine chronometer · Sundial · Water clock Wikipedia does not have an article with this exact name. ... Wiktionary (a portmanteau of wiki and dictionary) is a multilingual, Web-based project to create a free content dictionary, available in over 151 languages. ... Image File history File links Wikisource-logo. ... The original Wikisource logo. ... Encyclopædia Britannica, the eleventh edition The Encyclopædia Britannica Eleventh Edition (1910–1911) is perhaps the most famous edition of the Encyclopædia Britannica. ... This article is about the concept of time. ... This article is about the concept of time. ... While in the popular mind, eternity often simply means existing for an infinite, i. ... Arguments for eternity composed a particularly important area of philosophical debate among Greek, Jewish, Islamic, and Christian philosophers during the ancient and medieval periods. ... The Fountain of Eternal Life in Cleveland, Ohio Immortality (or eternal life) is the concept of living in physical or spiritual form for an infinite length of time, or in a state of timelessness. ... Deep time is the theory that Earth is billions of years old and thus had a long history of development and change. ... HIStory – Past, Present and Future, Book I is a double album by American singer Michael Jackson released in June 1995 and remains Jacksons most conflicting and controversial release. ... The past is the portion of the timeline that has already occurred; it is the opposite of the future. ... Present redirects here. ... For other uses, see Future (disambiguation). ... Futurology is the detailed critical inspection and reasoning of the state in which things will develop in the future on the basis of existing circumstances in history. ... Image File history File links Portal. ... A time scale specifies divisions of time. ... Wikipedia does not yet have an article with this exact name. ... UTC redirects here. ... Universal Time (UT) is a timescale based on the rotation of the Earth. ... International Atomic Time (TAI, from the French name Temps Atomique International) is a high-precision atomic time standard that tracks proper time on Earths geoid. ... This article is about the unit of time. ... This article is about the unit of time, angle and right ascension. ... The hour (symbol: h) is a unit of time. ... Sidereal time is time measured by the apparent diurnal motion of the vernal equinox, which is very close to, but not identical with, the motion of stars. ... Solar time is based on the idea that when the sun reaches its highest point in the sky, it is noon. ... Timezone and TimeZone redirect here. ... For other uses, see Clock (disambiguation). ... Horology is the study of the science and art of timekeeping devices. ... An astrarium, also called a planetarium, is the mechanical representation of the cyclic nature of astronomical objects in one timepiece. ... A marine chronometer is a timekeeper precise enough to be used as a portable time standard, used to determine longitude by means of celestial navigation. ... For other uses, see Sundial (disambiguation). ... A water clock or clepsydra is a device for measuring time by letting water regularly flow out of a container usually by a tiny aperture. ... Calendar · Day · Week · Month · Year · Tropical year · Julian · Gregorian · Islamic Look up day in Wiktionary, the free dictionary. ... For more details on each day of the week, see days of the week. ... Look up Month in Wiktionary, the free dictionary. ... A year (from Old English gÄ“r) is the time between two recurrences of an event related to the orbit of the Earth around the Sun. ... A tropical year is the length of time that the Sun, as viewed from the Earth, takes to return to the same position along the ecliptic (its path among the stars on the celestial sphere). ... The Julian calendar was a reform of the Roman calendar which was introduced by Julius Caesar in 46 BC and came into force in 45 BC (709 ab urbe condita). ... For the calendar of religious holidays and periods, see liturgical year. ... The Islamic calendar or Muslim calendar (Arabic: التقويم الهجري; at-taqwÄ«m al-hijrÄ«; Persian: تقویم هجري قمری ‎ taqwÄ«m-e hejri-ye qamari; also called the Hijri calendar) is the calendar used to date events in many predominantly Muslim countries, and used by Muslims everywhere to determine the proper day on which to celebrate...   Intercalation · Leap second · Leap year Chronology Astronomical chronology · Geologic Time · Geological history · Geochronology · Archaeological dating Calendar era · Regnal year · Chronicle · Timeline · Periodization Religion and Mythology Time and fate deities · Wheel of time · Kāla · Kalachakra · Prophecy · Dreamtime Philosophy Causality · Eternalism · Eternal return · Event · The Unreality of Time · A-series and B-series · B-Theory of time Endurantism · Four dimensionalism · Perdurantism · Presentism · Temporal finitism · Temporal parts Physical Sciences Time in physics · Spacetime · Absolute time and space · T-symmetry Arrow of time · Chronon · Fourth dimension · Planck epoch · Planck time · Time domain Intercalation is the insertioffn of an extra day, week or month into some calendar years to make the calendar follow the seasons. ... A leap second is a one-second adjustment to civil time in order to keep it close to the mean solar time. ... For the 1921 film starring Fatty Arbuckle, see Leap Year (film). ... For the novel by Michael Crichton, see Timeline (novel). ... Diagram of geological time scale. ... Geological time scale. ... Geochronology is the science of determining the age of rocks, fossils, and sediments. ... Dating material drawn from the archaeological record can made by a direct study of a artifact or may be deduced by association with materials found in the context the item is drawn from or inferred by its point of discovery in the sequence relative to datable contexts. ... A calendar era is the year numbering system used by a calendar. ... Regnal year: the year of the reign of a sovereign. ... Generally a chronicle (Latin chronica, from Greek Χρόνος) is historical account of facts and events in chronological order. ... For other uses, see Timeline (disambiguation). ... Periodization is the attempt to categorize or divide time into discrete named blocks. ... Wheel of time may refer to: The Wheel of time or history, a religious concept predominant in Buddhism and Hinduism The Wheel of Time, a fantasy book series by author Robert Jordan The Wheel of Time (computer game), an action first-person shooter based on the series The Timewheel, a... is the Sanskrit for time (from a root to enumerate; unrelated to black whence ). It denotes a fixed or right point in time (compare rtu, kairos). ... Kālacakra (Sanskrit कालचक्र; Tibetan དུས་ཀྱི་འཁོར་ལོ་ dus kyi khor lo) is a term used in Tantric Buddhism that means time-wheel or time-cycles. It refers both to a Tantric deity (Tib. ... For other uses, see Prophecy (disambiguation). ... opens chapter nine of The Dreaming Universe (1994) entitled The Dreamtime with a quote from The Last Wave, a film by Peter Weir: Aboriginals believe in two forms of time. ... Philosophy of space and time is the branch of philosophy concerned with the issues surrounding the ontology, epistemology, and character of space and time. ... Causality or causation denotes the relationship between one event (called cause) and another event (called effect) which is the consequence (result) of the first. ... Eternalism is a philosophical approach to the ontological nature of time. ... Eternal return or sometimes eternal recurrence is a concept originating from ancient Egypt and developed in the teachings of Pythagoras. ... This page is a candidate for speedy deletion because: this page is a test If you disagree with its speedy deletion, please explain why on its talk page or at Wikipedia:Speedy deletions. ... Wikisource has original text related to this article: The Unreality of Time To meet Wikipedias quality standards, this article or section may require cleanup. ... A-series and B-series are terms introduced by the Scottish idealist philosopher John McTaggart in 1908 which have become classic terms of reference in modern discussions of the philosophy of time, even outside the analytic tradition. ... The B-theory of time is a term, given to one a two positions taken by theorists, in the philosophy of time. ... This article or section is in need of attention from an expert on the subject. ... In the philosophy of time, four dimensionalism is the view that reality is a four-dimensional continuum composed of time and space (spacetime). ... Perdurantism or perdurance theory is a philosophical theory of persistence and identity. ... In the philosophy of time, presentism is the belief that neither the future nor the past exists. ... Temporal Parts are used in contemporary metaphysics in the debate over persistence of material objects. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... For other uses of this term, see Spacetime (disambiguation). ... In physics, the concept of absolute time and absolute space are hypothetical models in which time either runs at the same rate for all the observers in the universe or the rate of time of each observer can be scaled to the absolute time by multiplying the rate by a... T-symmetry is the symmetry of physical laws under a time-reversal transformation— The universe is not symmetric under time reversal, although in restricted contexts one may find this symmetry. ... This article or section does not cite its references or sources. ... A chronon is a hypothetical concept in theoretical physics intended to describe a quantum of time. ... For other uses, see Fourth dimension (disambiguation). ... Named after Max Planck, in cosmology the Planck epoch (or Planck Era) is the earliest period of time in the history of the universe, from zero to 10-43 seconds (one Planck time), during which all four fundamental forces were unified and elementary particles did not yet exist. ... In physics, the Planck time (tP), is the unit of time in the system of natural units known as Planck units. ... Time-domain is a term used to describe the analysis of mathematical functions, or real-life signals, with respect to time. ... Theory of relativity · Time dilation · Gravitational time dilation · Coordinate time · Proper time Psychology Consciousness and spacetime · Mental chronometry · Reaction time · Sense of time · Specious present Sociology and Anthropology Futures studies · Long Now Foundation · Time discipline · Time use research Economics Newtonian time in economics · Time value of money Related topics Space · Duration · Time capsule · Time travel · Time signature · System time · Carpe diem · Tempus fugit

v • d • e Time measurement and standards Major subjects Time · Chronometry · Orders of magnitude · Units of time · Metrology Time Portal International standards UTC · UT · TAI · ISO 31-1 · Second · DUT1 · Leap second · IERS Terrestrial Time · Geocentric Coordinate Time · Barycentric Coordinate Time -1... Time dilation is the phenomenon whereby an observer finds that anothers clock which is physically identical to their own is ticking at a slower rate as measured by their own clock. ... Gravitational time dilation is a consequence of Albert Einsteins theories of relativity and related theories which causes time to pass at different rates in regions of a different gravitational potential; the higher the local distortion of spacetime due to gravity, the slower time passes. ... Coordinate time is the interval of time independent of relativistic time dilation. ... In relativity, proper time is time measured by a single clock between events that occur at the same place as the clock. ... Space-time theories of consciousness relate the geometrical features of conscious experience, such as viewing things in space-time at a point, to the geometrical properties of the universe itself. ... // Definition and history Psychologists have investigated mental chronometry for over 100 years. ... Reaction time (RT) is the elapsed time between the presentation of a sensory stimulus and the subsequent behavioral response. ... Although the sense of time is not associated with a specific sensory system, the work of psychologists and neuroscientists indicates that our brains do have a system governing the perception of time. ... The specious present is the time duration wherein ones perceptions are considered to be in the present. ... Future studies reflects on how today’s changes (or the lack thereof) become tomorrow’s reality. ... The Long Now Foundation, established in 1996, is a private organization that seeks to become the seed of a very long-term cultural institution. ... In sociology and anthropology, time discipline is the general name given to social and economic rules, conventions, customs, and expectations governing the measurement of time, the social currency and awareness of time measurements, and peoples expectations concerning the observance of these customs by others. ... Time use research is a developing interdisciplinary field of study dedicated to knowing how people allocate their time during an average day. ... The time value of money is the premise that an investor prefers to receive a payment of a fixed amount of money today, rather than an equal amount in the future, all else being equal. ... This article is about the idea of space. ... A duration is an amount of time or a particular time interval. ... For other uses, see Time capsule (disambiguation). ... Time travel is a concept that has long fascinated humanity—whether it is Merlin experiencing time backwards, or religious traditions like Mohammeds trip to Jerusalem and ascent to heaven, returning before a glass knocked over had spilt its contents. ... The time signature (also known as meter signature) is a notational convention used in Western musical notation to specify how many beats are in each measure and what note value constitutes one beat. ... In computer science and computer programming, system time represents a computer systems notion of the passing of time. ... For other uses, see Carpe diem (disambiguation). ... Tempus fugit on a sundial Tempus fugit is a Latin expression meaning time flees, more commonly translated as time flies. It is frequently used as an inscription on clocks. ... A time scale specifies divisions of time. ... This article is about the concept of time. ... Wikipedia does not yet have an article with this exact name. ... // The pages linked in the right-hand column contain lists of times that are of the same order of magnitude (power of ten). ... Metrology (from Greek metron (measure), and -logy) is the science of measurement. ... Image File history File links Portal. ... UTC redirects here. ... Universal Time (UT) is a timescale based on the rotation of the Earth. ... International Atomic Time (TAI, from the French name Temps Atomique International) is a high-precision atomic time standard that tracks proper time on Earths geoid. ... ISO 31-1 is the part of international standard ISO 31 that defines names and symbols for quantities and units related to space and time. ... This article is about the unit of time. ... The time correction DUT1 is the difference between the Universal Time scale UT1 (which corresponds to the Earths rotation) and the Coordinated Universal Time (UTC) (which corresponds, except for a constant offset, to International Atomic Time (TAI)). DUT1 = UT1 - UTC DUT1 is maintained in the range -0. ... A leap second is a one-second adjustment to civil time in order to keep it close to the mean solar time. ... The International Earth Rotation and Reference Systems Service is the body responsible for maintaining global time and reference frame standards, notably through its Earth Orientation Parameter (EOP) and International Celestial Reference System (ICRS) groups. ... Terrestrial Time (TT) is the modern time standard for time on the surface of the Earth. ... Geocentric Coordinate Time (TCG) is a coordinate time standard intended to be used as the independent variable of time for all calculations pertaining to precession, nutation, the Moon, and artificial satellites of the Earth. ... Barycentric Coordinate Time (TCB) was defined in 1991 by the International Astronomical Union as one of the replacements for the ill-defined Barycentric Dynamical Time (TDB). ... Civil time · Minute · Hour · 12-hour clock · 24-hour clock · ISO 8601 Civil time is another name for mean solar time reckoned from midnight. ... This article is about the unit of time, angle and right ascension. ... The hour (symbol: h) is a unit of time. ... The 12-hour clock is a timekeeping convention in which the 24 hours of the day are divided into two periods called ante meridiem (a. ... The 24-hour clock is a convention of time keeping in which the day runs from midnight to midnight and is divided into 24 hours, numbered from 0 to 23. ... ISO 8601 is an international standard for date and time representations issued by the International Organization for Standardization (ISO). ... International Date Line · Solar time · Time zone · Daylight saving time · Time offset · Annum Obsolete standards Ephemeris time · Barycentric Dynamical Time · Greenwich Mean Time · Prime Meridian Time in physics Spacetime · Chronon · Cosmological decade · Planck epoch · Planck time · T-symmetry Theory of relativity · Time dilation · Gravitational time dilation · Coordinate time · Proper time “Date line” redirects here. ... Solar time is based on the idea that when the sun reaches its highest point in the sky, it is noon. ... Timezone and TimeZone redirect here. ... Although DST is common in Europe and North America, most of the worlds people do not use it. ... A time offset is defined by international convention as a number of hours and minutes from Coordinated Universal Time in Greenwich, England. ... Annum is a Latin noun meaning year. ... Ephemeris Time (ET) is a now obsolete time scale used in ephemerides of celestial bodies, in particular the Sun (as observed from the Earth), Moon, planets, and other members of the solar system. ... Barycentric Dynamical Time (TDB) was defined by the International Astronomical Union (IAU) in 1976 to be used as the relativistic replacement for the non-relativistic Ephemeris Time which had been used in the ephemerides starting in 1960. ... GMT redirects here. ... Location of the Prime Meridian Image:Prime Meridian. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... For other uses of this term, see Spacetime (disambiguation). ... A chronon is a hypothetical concept in theoretical physics intended to describe a quantum of time. ... A cosmological decade ( CÐ ) is a division of the lifetime of the cosmos. ... Named after Max Planck, in cosmology the Planck epoch (or Planck Era) is the earliest period of time in the history of the universe, from zero to 10-43 seconds (one Planck time), during which all four fundamental forces were unified and elementary particles did not yet exist. ... In physics, the Planck time (tP), is the unit of time in the system of natural units known as Planck units. ... T-symmetry is the symmetry of physical laws under a time-reversal transformation— The universe is not symmetric under time reversal, although in restricted contexts one may find this symmetry. ... -1... Time dilation is the phenomenon whereby an observer finds that anothers clock which is physically identical to their own is ticking at a slower rate as measured by their own clock. ... Gravitational time dilation is a consequence of Albert Einsteins theories of relativity and related theories which causes time to pass at different rates in regions of a different gravitational potential; the higher the local distortion of spacetime due to gravity, the slower time passes. ... Coordinate time is the interval of time independent of relativistic time dilation. ... In relativity, proper time is time measured by a single clock between events that occur at the same place as the clock. ... Time domain · Continuous time · Discrete time · Absolute time and space Horology Clock · Astrarium · Atomic clock · Hourglass · Marine chronometer · Radio clock · Sundial · Watch · Water clock History of timekeeping devices · Equation of time · Complication Calendar Day · Week · Month · Year · Decade · Century · Millennium Astronomical · Julian · Gregorian · Islamic · Lunisolar · Solar · Lunar · Epact · Intercalation · Leap year Time-domain is a term used to describe the analysis of mathematical functions, or real-life signals, with respect to time. ... A continuous signal or a continuous time signal is a varying quantity (a signal) that can be, or is expressed, as a continuous function of an independent variable, usually time. ... Discrete time is non-continuous time. ... In physics, the concept of absolute time and absolute space are hypothetical models in which time either runs at the same rate for all the observers in the universe or the rate of time of each observer can be scaled to the absolute time by multiplying the rate by a... Horology is the study of the science and art of timekeeping devices. ... For other uses, see Clock (disambiguation). ... An astrarium, also called a planetarium, is the mechanical representation of the cyclic nature of astronomical objects in one timepiece. ... “Nuclear Clock” redirects here. ... For other uses, see Hourglass (disambiguation). ... A marine chronometer is a timekeeper precise enough to be used as a portable time standard, used to determine longitude by means of celestial navigation. ... A radio clock A radio clock is a clock that is synchronized by a time code bit stream transmitted by a radio transmitter connected to a time standard such as an atomic clock. ... For other uses, see Sundial (disambiguation). ... For other uses, see Watch (disambiguation). ... A water clock or clepsydra is a device for measuring time by letting water regularly flow out of a container usually by a tiny aperture. ... The equation of time is the difference, over the course of a year, between time as read from a sundial and a clock. ... In horology terms, a complication in a mechanical timepiece is any feature beyond that of a simple hours, minutes, and seconds movement. ... Look up day in Wiktionary, the free dictionary. ... For more details on each day of the week, see days of the week. ... Look up Month in Wiktionary, the free dictionary. ... A year (from Old English gÄ“r) is the time between two recurrences of an event related to the orbit of the Earth around the Sun. ... For other senses of this word, see decade (disambiguation). ... A century (From the Latin cent, one hundred) is one hundred consecutive years. ... A millennium (pl. ... Astronomical year numbering is based on BCE/CE (or BC/AD) year numbering, but follows normal decimal integer numbering more strictly. ... The Julian calendar was a reform of the Roman calendar which was introduced by Julius Caesar in 46 BC and came into force in 45 BC (709 ab urbe condita). ... For the calendar of religious holidays and periods, see liturgical year. ... The Islamic calendar or Muslim calendar (Arabic: التقويم الهجري; at-taqwÄ«m al-hijrÄ«; Persian: تقویم هجري قمری ‎ taqwÄ«m-e hejri-ye qamari; also called the Hijri calendar) is the calendar used to date events in many predominantly Muslim countries, and used by Muslims everywhere to determine the proper day on which to celebrate... A lunisolar calendar is a calendar whose date indicates both the moon phase and the time of the solar year. ... A solar calendar is a calendar whose dates indicate the position of the earth on its revolution around the sun (or equivalently the apparent position of the sun moving on the celestial sphere). ... A lunar calendar is a calendar that is based on cycles of the moon phase. ... The epact (from Greek: epaktai hèmerai = added days) is, as the second Canon of the Gregorian Calendar reform puts it, nothing else than the number of days which the common solar year of 365 days surpasses the common lunar year of 354 days (Latin: Epacta nihil aliud est quam... Intercalation is the insertioffn of an extra day, week or month into some calendar years to make the calendar follow the seasons. ... For the 1921 film starring Fatty Arbuckle, see Leap Year (film). ... Tropical year · Equinox · Solstice · Days of the week · Calculating the day of the week · Dominical letter Archaeology & geology International Commission on Stratigraphy · Geologic Time · Archaeological dating Astronomical chronology Nuclear time scale · Precession · Sidereal time · Galactic year Unusual units Fortnight · Jiffy · Lustrum · Saeculum · Shake · Tide Related topics Chronology · Duration · System time · Mental chronometry · Time value of money · Timekeeper

v • d • e Chronology Major subjects Time · Astronomy · Geology · Paleontology · Archaeology · History Time Portal Eras and Epochs Calendar Eras: Ab urbe condita · Anno Domini / Common Era · Anno Mundi · Spanish era · Before Present · Hijri Egyptian · Sothic cycle · Hindu units of measurement · Hindu Yugas A tropical year is the length of time that the Sun, as viewed from the Earth, takes to return to the same position along the ecliptic (its path among the stars on the celestial sphere). ... For other uses, see Equinox (disambiguation). ... “Summer solstice” redirects here. ... This article is about days of the week. ... This article details various mathematical algorithms to calculate the day of the week for any particular date in the past or future. ... The days of the year are sometimes designated letters A, B, C, D, E, F and G in a cycle of 7 as an aid for finding the day of week of a given calendar date and in calculating Easter. ... The International Commission on Stratigraphy concerns itself with stratigraphy on a global scale. ... Diagram of geological time scale. ... Dating material drawn from the archaeological record can made by a direct study of a artifact or may be deduced by association with materials found in the context the item is drawn from or inferred by its point of discovery in the sequence relative to datable contexts. ... The precession of Earths axis of rotation with respect to inertial space is also called the precession of the equinoxes. ... Sidereal time is time measured by the apparent diurnal motion of the vernal equinox, which is very close to, but not identical with, the motion of stars. ... // Galactic time NGC 4414, a typical spiral galaxy alike our Milky Way Galactic time, not to confuse with siderial time, is the time that is described by our spin relative to the center of the galaxy. ... Look up fortnight in Wiktionary, the free dictionary. ... The term jiffy (or jiffie) is used in different applications for various different short periods of time, usually 1/60 of a second. ... Lustrum was a sacrifice for expiation and purification offered by one of the censors of Rome in name of the Roman people at the close of the taking of the census, and which took place after a period of five years, so that the name came to denote a period... A saeculum is a length of time roughly equal to the lifetime of a person, or about 90 years. ... A shake is an informal unit of time equal to 10 nanoseconds, or 10-8 seconds. ... A tide is an obsolete or archaic term for time, period or season, such as eventide, shrovetide, Eastertide, etc. ... For the novel by Michael Crichton, see Timeline (novel). ... A duration is an amount of time or a particular time interval. ... In computer science and computer programming, system time represents a computer systems notion of the passing of time. ... // Definition and history Psychologists have investigated mental chronometry for over 100 years. ... The time value of money is the premise that an investor prefers to receive a payment of a fixed amount of money today, rather than an equal amount in the future, all else being equal. ... Look up timekeeper in Wiktionary, the free dictionary. ... For the novel by Michael Crichton, see Timeline (novel). ... This article is about the concept of time. ... For other uses, see Astronomy (disambiguation). ... This article includes a list of works cited but its sources remain unclear because it lacks in-text citations. ... Paleontology, palaeontology or palæontology (from Greek: paleo, ancient; ontos, being; and logos, knowledge) is the study of prehistoric life forms on Earth through the examination of plant and animal fossils. ... For referencing in Wikipedia, see Wikipedia:Citing sources. ... HIStory – Past, Present and Future, Book I is a double album by American singer Michael Jackson released in June 1995 and remains Jacksons most conflicting and controversial release. ... Image File history File links Download high resolution version (800x697, 123 KB) fr:: Montre gousset cs:: Kapesní hodinky de: Deutsch: Taschenuhr en: English: Pocket watch it: Italiano: Orologio da taschino (cipolla) es: Español: Reloj de bolsillo Template:ગુજરાતી ગુજરાતી: ખિસ્સામાં રાખવાની ઘડિયાળ ja: 日本語: 懐中時計 pl: Polski: Zegarek kieszonkowy pt: Português: Relógio de bolso... Image File history File links Portal. ... An era is a long period of time with different technical and colloquial meanings, and usages in language. ... In chronology, an epoch (or epochal date, or epochal event) means an instant in time chosen as the origin of a particular era. ... A calendar era is the year numbering system used by a calendar. ... Ab urbe condita (related with Anno urbis conditae: AUC or a. ... AD redirects here. ... BCE redirects here. ... Anno Mundi (AM, in the year of the world) refers to a Calendar era counting from the creation of the world. ... The Spanish era or Era of the Caesars refers to the dating system used in Hispania until the fourteenth century and the adoption of Anno Domini. ... Before Present (BP) years are the units of time (counted backwards to the past) used to report raw radiocarbon ages and dates referenced to the BP scale origin in the year AD 1950 (identical to 1950 CE). ... The Islamic calendar or Muslim calendar (Arabic: التقويم الهجري; at-taqwÄ«m al-hijrÄ«; Persian: تقویم هجري قمری ‎ taqwÄ«m-e hejri-ye qamari; also called the Hijri calendar) is the calendar used to date events in many predominantly Muslim countries, and used by Muslims everywhere to determine the proper day on which to celebrate... The Sothic cycle or Canicular period is a period of 1461 ancient Egyptian years (of 365 days) or 1460 Julian years (averaging 365. ... // The astronomical time cycles mentioned in ancient Hindu astronomical and Puranic texts are remarkably similar to each other. ... Yuga (Devnāgari: युग) in Hindu philosophy refers to an epoch or era within a cycle of four ages: the Satya Yuga (or Krita Yuga), the Treta Yuga, the Dvapara Yuga and finally the Kali Yuga. ... Regnal year: Canon of Kings · King lists · Limmu · Seleucid era · Era name: Chinese · Japanese · Korean Calendars Pre-Julian Roman · Original Julian · Proleptic Julian · Revised Julian Gregorian · Proleptic Gregorian · Old Style and New Style Regnal year: the year of the reign of a sovereign. ... The Canon of Kings was a dated list of kings used by ancient astronomers as a convenient means to date astronomical phenomena, such as eclipses. ... Limmu was an Assyrian eponym. ... Coin of Philip V of Macedon (ruled 221–179 BC). ... An era name was assigned as the name of each year by the leader (emperor or king) of the East Asian countries of China, Korea, Japan, and Vietnam during some portion of their history. ... The Roman calendar changed its form several times in the time between the foundation of Rome and the fall of the Roman Empire. ... The Julian calendar was a reform of the Roman calendar which was introduced by Julius Caesar in 46 BC and came into force in 45 BC (709 ab urbe condita). ... The proleptic Julian calendar is produced by extending the Julian calendar to dates preceding its official introduction in 45 BC. Historians since Bede have traditionally represented the years preceding AD 1 as 1 BC, 2 BC, etc. ... The Revised Julian calendar is a calendar that was considered for adoption by the Eastern Orthodox churches at a synod in Istanbul in May 1923. ... For the calendar of religious holidays and periods, see liturgical year. ... The proleptic Gregorian calendar is produced by extending the Gregorian Calendar to dates preceding its official introduction in 1582. ... Old Style redirects here. ... Lunisolar · Solar · Lunar · Islamic · Chinese sexagenary cycle A lunisolar calendar is a calendar whose date indicates both the moon phase and the time of the solar year. ... A solar calendar is a calendar whose dates indicate the position of the earth on its revolution around the sun (or equivalently the apparent position of the sun moving on the celestial sphere). ... A lunar calendar is a calendar that is based on cycles of the moon phase. ... The Islamic calendar or Muslim calendar (Arabic: التقويم الهجري; at-taqwÄ«m al-hijrÄ«; Persian: تقویم هجري قمری ‎ taqwÄ«m-e hejri-ye qamari; also called the Hijri calendar) is the calendar used to date events in many predominantly Muslim countries, and used by Muslims everywhere to determine the proper day on which to celebrate... The Chinese sexagenary cycle (Chinese: ; pinyin: ) is a cyclic numeral system of 60 combinations of the two basic cycles, the ten Heavenly Stems (天干; tiāngān) and the twelve Earthly Branches (地支; dìzhÄ«). These have been traditionally used as a means of numbering days and years, not only in China... Astronomical year numbering · ISO week date Astronomic time and techniques Astronomical chronology · Cosmic Calendar · Ephemeris · Galactic year · Metonic cycle · Milankovitch cycles Geologic time and techniques Deep time · Geological history · Eon · Eras · Periods · Faunal stage Chronostratigraphy · Geochronology · Isotope geochemistry · Law of superposition · Optical dating · Samarium-neodymium dating Archaeological techniques Dating methodology Absolute dating · Incremental dating · Archaeomagnetic dating · Dendrochronology · Glottochronology · Ice core · Lichenometry · Paleomagnetism · Radiocarbon dating · Radiometric dating · Tephrochronology · Thermoluminescence dating · Uranium-lead dating Relative dating · Seriation · Stratification Astronomical year numbering is based on BCE/CE (or BC/AD) year numbering, but follows normal decimal integer numbering more strictly. ... The ISO week date system is a leap week calendar system that is part of the ISO 8601 date and time standard. ... An ephemeris (plural: ephemerides) (from the Greek word ephemeros = daily) is a device giving the positions of astronomical objects in the sky. ... // Galactic time NGC 4414, a typical spiral galaxy alike our Milky Way Galactic time, not to confuse with siderial time, is the time that is described by our spin relative to the center of the galaxy. ... The Metonic cycle or Enneadecaeteris in astronomy and calendar studies is a particular approximate common multiple of the year (specifically, the seasonal tropical year) and the synodic month. ... Milankovitch cycles are the collective effect of changes in the Earths movements upon its climate, named after Serbian civil engineer and mathematician Milutin Milanković. The eccentricity, axial tilt, and precession of the Earths orbit vary in several patterns, resulting in 100,000 year ice age cycles of the... Diagram of geological time scale. ... Deep time is the theory that Earth is billions of years old and thus had a long history of development and change. ... Geological time scale. ... In general usage, an eon (sometimes spelled æon) is an arbitrarily designated period of time. ... A geologic era is a subdivision of geologic time that is a separate classification that divides the Phanerozoic Eon into three parts timeframes. ... A geologic period is a subdivision of geologic time that divides an era into smaller timeframes. ... Faunal stages are a subdivision of geologic time used primarily by paleontologists who study fossils rather than by geologists who study rock formations. ... Chronostratigraphy is the branch of stratigraphy that studies the age of rock strata in relation to time. ... Geochronology is the science of determining the age of rocks, fossils, and sediments. ... Isotope geochemistry is an aspect of Geology based upon study of the relative and absolute concentrations of the elements and their isotopes in the Earth. ... See here for the superposition principle of physics. ... Optical dating is a method of determining how long ago minerals were last exposed to daylight. ... This article needs to be cleaned up to conform to a higher standard of quality. ... Dating material drawn from the archaeological record can made by a direct study of a artifact or may be deduced by association with materials found in the context the item is drawn from or inferred by its point of discovery in the sequence relative to datable contexts. ... Absolute dating is the process of determining a specific archaeological date. ... Incremental dating techniques allow the construction of year-by-year annual chronologies, which can be fixed ( linked to the present day and thus calendar or sidereal time) or floating. ... Archaeomagnetism (adjective archaeomagnetic) is the science of how to interpret signatures of the Earths magnetic field at past times that are recorded in archaeological materials. ... The growth rings of an unknown tree species, at Bristol Zoo, England Pinus taeda Cross section showing annual rings, Cheraw, South Carolina Pine stump showing growth rings Dendrochronology or tree-ring dating is the method of scientific dating based on the analysis of tree-ring growth patterns. ... Glottochronology refers to methods in historical linguistics used to estimate the time at which languages diverged, based on the assumption that the basic (core) vocabulary of a language changes at a constant average rate. ... Ice Core sample taken from drill. ... Lichens are a symbiotic relationship between algal and fungal communities and they increase in size radially as they grow. ... Paleomagnetism refers to the study of the record of the Earths magnetic field preserved in various magnetic minerals through time. ... Radiocarbon dating is a radiometric dating method that uses the naturally occurring isotope carbon-14 (14C) to determine the age of carbonaceous materials up to about 60,000 years. ... Radiometric dating (often called radioactive dating) is a technique used to date materials, based on a comparison between the observed abundance of particular naturally occurring radioactive isotopes and their known decay rates. ... Tephrochronology is a geochronolgical technique that utilises discreet layers of tephra—volcanic ash from a single eruption— to create a chronological framework in which palaeoenvironmental or archaeological records can be placed. ... Thermoluminescence (TL) dating is the determination by means of measuring the accumulated radiation dose of the time elapsed since material containing crystalline minerals was either heated (lava, ceramics) or exposed to sunlight (sediments). ... Radiometric dating is a technique used to date materials based on a knowledge of the decay rates of naturally occurring isotopes, and the current abundances. ... Before the advent of absolute dating in the 20th century, archaeologists and geologists were largely limited to the use of Relative Dating techniques. ... In archaeology, seriation is a method in relative dating in which artifacts of numerous sites, in the same culture, are placed in chronological order. ... In archaeology, especially in the course of excavation, stratification is of major interest and significance. ... Genetic techniques Amino acid dating · Molecular clock Related topics Chronicle · New Chronology · Periodization · Synchronoptic view · Timeline · Year zero · Circa · Floruit