The terms anno Domini (AD) and before Christ (BC) are used when designating years in the Julian and Gregorian calendars. The term anno Domini is Medieval Latin and means "in the year of the Lord" but is often presented using "our Lord" instead of "the Lord", taken from the full original phrase "anno Domini nostri Jesu Christi", which translates to "in the year of our Lord Jesus Christ". The form "BC" is specific to English, and equivalent abbreviations are used in other languages: the Latin form, rarely used in English, is Ante Christum natum (ACN) or Ante Christum (AC).
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 of such a system. A calendar can also mean a list of planned events, such as a court calendar, or a partly or fully chronological list of documents, such as a calendar of wills.
The Hijri calendar, also known in English as the Muslim calendar and Islamic calendar, is a lunar calendar consisting of 12 lunar months in a year of 354 or 355 days. It is used to determine the proper days of Islamic holidays and rituals, such as the annual fasting and the annual season for the great pilgrimage. In almost all countries where the predominant religion is Islam, the civil calendar is the Gregorian calendar, with Syriac month-names used in the Levant and Mesopotamia but the religious calendar is the Hijri one.
Intercalation or embolism in timekeeping is the insertion of a leap day, week, or month into some calendar years to make the calendar follow the seasons or moon phases. Lunisolar calendars may require intercalations of both days and months.
The New Year is the time or day at which a new calendar year begins and the calendar's year count increments by one. Many cultures celebrate the event in some manner. In the Gregorian calendar, the most widely used calendar system today, New Year occurs on January 1. This was also the first day of the year in the original Julian calendar and the Roman calendar.
In chronology and periodization, an epoch or reference epoch is an instant in time chosen as the origin of a particular calendar era. The "epoch" serves as a reference point from which time is measured.
A solar calendar is a calendar whose dates indicate the season or almost equivalently the apparent position of the Sun relative to the stars. The Gregorian calendar, widely accepted as a standard in the world, is an example of a solar calendar. The main other types of calendar are lunar calendar and lunisolar calendar, whose months correspond to cycles of Moon phases. The months of the Gregorian calendar do not correspond to cycles of the Moon phase.
The Iranian calendars or Iranian chronology are a succession of calendars created and used for over two millennia in Iran, also known as Persia. One of the longest chronological records in human history, the Iranian calendar has been modified many times for administrative, climatic, and religious purposes. The most influential person in laying the frameworks for the calendar and its precision was the 11th century Persian polymath, hakim Omar Khayyam. The modern Iranian calendar is currently the official civil calendar in Iran and Afghanistan.
The Thai solar calendar was adopted by King Chulalongkorn in 1888 CE as the Siamese version of the Gregorian calendar, replacing the Thai lunar calendar as the legal calendar in Thailand. Years are now counted in the Buddhist Era (B.E.): พุทธศักราช, พ.ศ.RTGS: Phutthasakkarat which is 543 years ahead of the Gregorian calendar.
The history of calendars covers practices with ancient roots as people created and used various methods to keep track of days and larger divisions of time. Calendars commonly serve both cultural and practical purposes and are often connected to astronomy and agriculture.
A calendar era is the period of time elapsed since one epoch of a calendar and, if it exists, before the next one. For example, it is the year 2023 as per the Gregorian calendar, which numbers its years in the Western Christian era.
The Ethiopian calendar, or Ge'ez calendar is the official calendar of Ethiopia. It is used as both the civil calendar and an ecclesiastical calendar. It is the liturgical year for Ethiopian and Eritrean Christians belonging to the Orthodox Tewahedo Churches, Eastern Catholic Churches, and Eastern Protestant Christian P'ent'ay Churches. The Ethiopian calendar is a solar calendar that has much in common with the Coptic calendar of the Coptic Orthodox Church of Alexandria and Coptic Catholic Church, but like the Julian calendar, it adds a leap day every four years without exception, and begins the year on 29 or 30 August in the Julian calendar. A gap of seven to eight years between the Ethiopian and Gregorian calendars results from an alternative calculation in determining the date of the Annunciation.
The Buddhist calendar is a set of lunisolar calendars primarily used in Tibet, Cambodia, Laos, Myanmar, India, Sri Lanka, and Thailand as well as in Malaysia, Singapore and Vietnam by Chinese populations for religious or official occasions. While the calendars share a common lineage, they also have minor but important variations such as intercalation schedules, month names and numbering, use of cycles, etc. In Thailand, the name Buddhist Era is a year numbering system shared by the traditional Thai lunar calendar and by the Thai solar calendar.
Vikram Samvat, also known as the Vikrami calendar or, in Nepal, Nepal Sambat, is a Hindu calendar historically used in the Indian subcontinent and still used in several states.. It is a lunisolar calendar, using twelve to thirteen lunar months each solar sidereal years. The year count of the Vikram Samvat calendar is usually 57 years ahead of the Gregorian calendar, except during January to April, when it is ahead by 56 years.
The Hijri year or era is the era used in the Islamic lunar calendar. It begins its count from the Islamic New Year in which Muhammad and his followers migrated from Mecca to Yathrib in 622 CE. This event, known as the Hijrah, is commemorated in Islam for its role in the founding of the first Muslim community (ummah).
In Thailand, two main calendar systems are used alongside each other: the Thai solar calendar, based on the Gregorian calendar and used for official and most day-to-day purposes, and the Thai lunar calendar, used for traditional events and Buddhist religious practices.
The Arabic names of the months of the Gregorian calendar are usually phonetic Arabic pronunciations of the corresponding month names used in European languages. An exception is the Syriac calendar used in Iraq and the Levant, whose month names are inherited via Classical Arabic from the Babylonian and Hebrew lunisolar calendars and correspond to roughly the same time of year.
The Burmese calendar is a lunisolar calendar in which the months are based on lunar months and years are based on sidereal years. The calendar is largely based on an older version of the Hindu calendar, though unlike the Indian systems, it employs a version of the Metonic cycle. The calendar therefore has to reconcile the sidereal years of the Hindu calendar with the Metonic cycle's near tropical years by adding intercalary months and days at irregular intervals.
The Gregorian calendar is the calendar used in most parts of the world. It went into effect in October 1582 following the papal bull Inter gravissimas issued by Pope Gregory XIII, which introduced it as a modification of, and replacement for, the Julian calendar. The principal change was to space leap years differently so as to make the average calendar year 365.2425 days long, more closely approximating the 365.2422-day 'tropical' or 'solar' year that is determined by the Earth's revolution around the Sun.
The adoption of the Gregorian Calendar was an event in the early modern history of most cultures and societies, marking a change from their traditional dating system to the modern dating system – the Gregorian calendar – that is widely used around the world today. Some states adopted the new calendar from 1582, some did not do so before the early twentieth century, and others did so at various dates between. A few still have not, but except for these, the Gregorian calendar is now the world's civil calendar universally, although in many places an old style calendar remains used in religious or traditional contexts. During – and for some time after – the change between systems, it has been common to use the terms "Old Style" and "New Style" when giving dates, to indicate which calendar was used to reckon them.
