The traditional China calendar, or Former Calendar, Traditional Calendar or Lunar Calendar, is a lunisolar calendar which reckons years, months and days according to astronomical phenomena. It is defined by GB/T 33661-2017, "Calculation and promulgation of the Chinese calendar", issued by the Standardisation Administration of China on 12 May 2017.
The Julian calendar, proposed by Julius Caesar in 46 BC, was a reform of the Roman calendar. It took effect on 1 January 45 BC, by edict. It was the predominant calendar in the Roman world, most of Europe, and in European settlements in the Americas and elsewhere, until it was refined and gradually replaced by the Gregorian calendar, promulgated in 1582 by Pope Gregory XIII.
A leap year is a calendar year containing one additional day added to keep the calendar year synchronized with the astronomical or seasonal year. Because seasons and astronomical events do not repeat in a whole number of days, calendars that have the same number of days in each year drift over time with respect to the event that the year is supposed to track. By inserting an additional day or month into the year, the drift can be corrected. A year that is not a leap year is called a common year.
A week is a time unit equal to seven days. It is the standard time period used for cycles of rest days in most parts of the world, mostly alongside—although not strictly part of—the Gregorian calendar.
The proleptic Julian calendar is produced by extending the Julian calendar backwards to dates preceding AD 8 when the quadrennial leap year stabilized. The leap years that were actually observed between the implementation of the Julian calendar in 45 BC and AD 8 were erratic: see the Julian calendar article for details.
The Coptic calendar, also called the Alexandrian calendar, is a liturgical calendar used by the Coptic Orthodox Church and also used by the farming populace in Egypt. This calendar is based on the ancient Egyptian calendar. To avoid the calendar creep of the latter, a reform of the ancient Egyptian calendar was introduced at the time of Ptolemy III which consisted of the intercalation of a sixth epagomenal day every fourth year. However, this reform was opposed by the Egyptian priests, and the reform was not adopted until 25 BC, when the Roman Emperor Augustus imposed the Decree upon Egypt as its official calendar. To distinguish it from the Ancient Egyptian calendar, which remained in use by some astronomers until medieval times, this reformed calendar is known as the Coptic calendar. Its years and months coincide with those of the Ethiopian calendar but have different numbers and names.
The 38th century BC was a century which lasted from the year 3800 BC to 3701 BC.
A calendar era is the year numbering system used by a calendar. For example, the Gregorian calendar numbers its years in the Western Christian era. The instant, date, or year from which time is marked is called the epoch of the era. There are many different calendar eras such as Saka Era.
The sexagenary cycle, also known as the Stems-and-Branches or ganzhi, is a cycle of sixty terms used for reckoning time in China and the rest of the East Asian cultural sphere. It appears as a means of recording days in the first Chinese written texts, the Shang oracle bones of the late second millennium BC. Its use to record years began around the middle of the 3rd century BC. The cycle and its variations have been an important part of the traditional calendrical systems in Chinese-influenced Asian states and territories, particularly those of Japan, Korea, and Vietnam, with the old Chinese system still in use in Taiwan.
The Doomsday rule is an algorithm of determination of the day of the week for a given date. It provides a perpetual calendar because the Gregorian calendar moves in cycles of 400 years.
The Ethiopian calendar or Eritrean calendar is the principal calendar used in Ethiopia and also serves as the liturgical year for Christians in Eritrea and Ethiopia belonging to the Eritrean Orthodox Tewahedo Church, Ethiopian Orthodox Tewahedo Church, Eastern Catholic Churches, the Coptic Orthodox Church of Alexandria, and Ethiopian-Eritrean Evangelicalism. It is a solar calendar which in turn derives from the Egyptian calendar, but like the Julian calendar, it adds a leap day every four years without exception, and begins the year on August 29 or August 30 in the Julian calendar. A gap of 7–8 years between the Ethiopian and Gregorian calendars results from an alternative calculation in determining the date of the Annunciation.
Anno Mundi, abbreviated as AM, or Year After Creation, is a calendar era based on the biblical accounts of the creation of the world and subsequent history. Two such calendar eras have seen notable use historically:
442 is a year in the 5th century of the Gregorian calendar.
Year zero does not exist in the anno Domini system usually used to number years in the Gregorian calendar and in its predecessor, the Julian calendar. In this system, the year 1 BC is followed by AD 1. However, there is a year zero in astronomical year numbering and in ISO 8601:2004 as well as in all Buddhist and Hindu calendars.
420 AD is a year in the 5th century of the Gregorian calendar.
MÁVAG was a Hungarian rail vehicle producer. MÁVAG company was the second largest industrial enterprise after the Manfréd Weiss Steel and Metal Works in the Hungarian half of the Austro-Hungarian Monarchy. MÁVAG was the property of the Kingdom of Hungary. After the World War II MÁVAG was nationalized, and "Királyi" ("Royal") was removed from its name.
The Republic of China Calendar is the official calendar of the Republic of China. It is used to number the years for official purposes only in Taiwan area after 1949. It was used in Chinese mainland from 1912 until the establishment of the People's Republic of China in 1949.
Rata Die (R.D.) is a system for assigning numbers to calendar days, independent of any calendar, for the purposes of calendrical calculations. It was named by Howard Jacobson. The same system was used earlier, e.g., the REXX programming language since about 1980:
The base date of 1 January 0001 is determined by extending the current Gregorian calendar backward.
The Gregorian calendar is the most widely used civil calendar in the world. It is named after Pope Gregory XIII, who introduced it in October 1582. The calendar spaces leap years to make the average year 365.2425 days long, approximating the 365.2422-day tropical year that is determined by the Earth's revolution around the Sun. The rule for leap years is:
Every year that is exactly divisible by four is a leap year, except for years that are exactly divisible by 100, but these centurial years are leap years if they are exactly divisible by 400. For example, the years 1700, 1800, and 1900 are not leap years, but the year 2000 is.
The proleptic Gregorian calendar is produced by extending the Gregorian calendar backward to dates preceding its official introduction in 1582. In countries that adopted the Gregorian calendar later, dates occurring in the interim are sometimes "Gregorianized" as well. For example, George Washington was born on February 11, 1731, as Great Britain and its possessions were using the Julian calendar with English years starting on March 25 until September 1752. After the switch, that day became February 22, 1732, which is the date commonly given as Washington's birthday.
