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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 Julian calendar, proposed by Julius Caesar in 708 AUC (46 BC), was a reform of the Roman calendar. It took effect on 1 January 709 AUC (45 BC), by edict. It was designed with the aid of Greek mathematicians and Greek astronomers such as Sosigenes of Alexandria.
AD 8 (VIII) was a leap year starting on Sunday of the Julian calendar. In the Roman Empire, it was known as the Year of the Consulship of Camillus and Quinctilianus. The denomination "AD 8" for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.
A leap year is a calendar year containing an 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 calendar obtained by extension earlier in time than its invention or implementation is called the "proleptic" version of the calendar. Likewise, the proleptic Gregorian calendar is occasionally used to specify dates before the introduction of the Gregorian calendar in 1582. Because the Julian calendar was used before that time, one must explicitly state that a given quoted date is based on the proleptic Gregorian calendar if that is the case.
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.
The Gregorian calendar is the calendar used in most of the world. It is named after Pope Gregory XIII, who introduced it in October 1582.
The Julian calendar itself was introduced by Julius Caesar, and as such is older than the introduction of the Anno Domini era (or the "Common Era"), counting years since the birth of Christ as calculated by Dionysus Exiguus in the 6th century, and widely used in medieval European annals since about the 8th century, notably by Bede. The proleptic Julian calendar uses Anno Domini throughout, including for dates of Late Antiquity when the Julian calendar was in use but Anno Domini wasn't, and for times predating the introduction of the Julian calendar. Years are given cardinal numbers, using inclusive counting (AD 1 is the first year of the Anno Domini era, immediately preceded by 1 BC, the first year preceding the Anno Domini era, there is no "zeroth" year). Thus, the year 1 BC of the proleptic Julian calendar is a leap year.
Gaius Julius Caesar, known by his nomen and cognomen Julius Caesar, was a populist Roman dictator, politician, and military general who played a critical role in the events that led to the demise of the Roman Republic and the rise of the Roman Empire. He was also a historian and wrote Latin prose.
The terms anno Domini (AD) and before Christ (BC) are used to label or number years in the Julian and Gregorian calendars. The term anno Domini is Medieval Latin and means "in the year of the Lord", but is often presented using "our Lord" instead of "the Lord", taken from the full original phrase "anno Domini nostri Jesu Christi", which translates to "in the year of our Lord Jesus Christ".
Common Era (CE) is one of the notation systems for the world's most widely used calendar era. BCE is the era before CE. BCE and CE are alternatives to the Dionysian BC and AD system respectively. The Dionysian era distinguishes eras using AD and BC. Since the two notation systems are numerically equivalent, "2019 CE" corresponds to "AD 2019" and "400 BCE" corresponds to "400 BC". Both notations refer to the Gregorian calendar. The year-numbering system used by the Gregorian calendar is used throughout the world today, and is an international standard for civil calendars.
This is to be distinguished from the astronomical year numbering, introduced in 1740 by French astronomer Jacques Cassini, which considers each New Year an integer on a time axis, with year 0 corresponding to 1 BC, and "year −1" corresponding to 2 BC, so that in this system, Julian leap years have a number divisible by four.
Astronomical year numbering is based on AD/CE year numbering, but follows normal decimal integer numbering more strictly. Thus, it has a year 0; the years before that are designated with negative numbers and the years after that are designated with positive numbers. Astronomers use the Julian calendar for years before 1582, including the year 0, and the Gregorian calendar for years after 1582, as exemplified by Jacques Cassini (1740), Simon Newcomb (1898) and Fred Espenak (2007).
Jacques Cassini was a French astronomer, son of the famous Italian astronomer Giovanni Domenico Cassini.
New Year is the time or day at which a new calendar year begins and the calendar's year count increments by one.
The determination of leap years in the proleptic Julian calendar (in either numbering) is distinct from the question of which years were historically considered leap years during the Roman era, due to the leap year error: Between 45 BC and AD 8, the leap day was somewhat unsystematic.Thus there is no simple way to find an equivalent in the proleptic Julian calendar of a date quoted using either the Roman pre-Julian calendar or the Julian calendar before AD 8. The year 46 BC itself is a special case: because of the historical introduction of the Julian calendar in that year, it was allotted 445 days. Before then, the Roman Republican calendar used a system of intercalary months rather than leap days.
The Roman Empire was the post-Republican period of ancient Rome, consisting of large territorial holdings around the Mediterranean sea in Europe, North Africa and West Asia ruled by emperors. From the accession of Caesar Augustus to the military anarchy of the third century, it was a principate with Italy as metropole of the provinces and its city of Rome as sole capital. The Roman Empire was then ruled by multiple emperors and divided into a Western Roman Empire, based in Milan and later Ravenna, and an Eastern Roman Empire, based in Nicomedia and later Constantinople. Rome remained the nominal capital of both parts until 476 AD, when it sent the imperial insignia to Constantinople following the capture of Ravenna by the barbarians of Odoacer and the subsequent deposition of Romulus Augustus. The fall of the Western Roman Empire to Germanic kings, along with the hellenization of the Eastern Roman Empire into the Byzantine Empire, is conventionally used to mark the end of Ancient Rome and the beginning of the Middle Ages.
The Roman calendar was the calendar used by the Roman kingdom and republic. The term often includes the Julian calendar established by the reforms of the dictator Julius Caesar and emperor Augustus in the late 1st century BC and sometimes includes any system dated by inclusive counting towards months' kalends, nones, and ides in the Roman manner. The term usually excludes the Alexandrian calendar of Roman Egypt, which continued the unique months of that land's former calendar; the Byzantine calendar of the later Roman Empire, which usually dated the Roman months in the simple count of the ancient Greek calendars; and the Gregorian calendar, which refined the Julian system to bring it into still closer alignment with the solar year and is the basis of the current international standard.
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.
AD 1 (I), 1 AD or 1 CE is the epoch year for the Anno Domini calendar era. It was the first year of the Common Era (CE), of the 1st millennium and of the 1st century. It was a common year starting on Saturday or Sunday, a common year starting on Saturday by the proleptic Julian calendar, and a common year starting on Monday by the proleptic Gregorian calendar. In its time, year 1 was known as the Year of the Consulship of Caesar and Paullus, named after Roman consuls Gaius Caesar and Lucius Aemilius Paullus, and less frequently, as year 754 AUC within the Roman Empire. The denomination "AD 1" for this year has been in consistent use since the mid-medieval period when the anno Domini (AD) calendar era became the prevalent method in Europe for naming years. It was the beginning of the Christian/Common era. The preceding year is 1 BC; there is no year 0 in this numbering scheme. The Anno Domini dating system was devised in AD 525 by Dionysius Exiguus.
Julian day is the continuous count of days since the beginning of the Julian Period and is used primarily by astronomers, and in software for easily calculating elapsed days between two events.
An epoch, for the purposes of chronology and periodization, 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.
Year 1 BC was a common year starting on Friday or Saturday of the Julian calendar and a leap year starting on Thursday of the Proleptic Julian calendar. It is also a leap year starting on Saturday, in the Proleptic Gregorian calendar. At the time, it was known as the Year of the Consulship of Lentulus and Piso. The denomination 1 BC for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years. The following year is 1 AD in the widely used Julian calendar, which does not have a "year zero".
Year 3 BC was a common year starting on Wednesday or Thursday of the Julian calendar and a common year starting on Tuesday of the Proleptic Julian calendar. At the time, it was known as the Year of the Consulship of Lentulus and Messalla. The denomination 3 BC for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.
Year 5 BC was a common year starting on Monday or Tuesday of the Julian calendar and a leap year starting on Saturday of the Proleptic Julian calendar. In the Roman world, it was known as the Year of the Consulship of Augustus and Sulla. The denomination 5 BC for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.
Year 9 BC was either a common year starting on Wednesday, Thursday or Friday or a leap year starting on Thursday of the Julian calendar and a leap year starting on Monday of the Proleptic Julian calendar. At the time, it was known as the Year of the Consulship of Drusus and Crispinus. The denomination 9 BC for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.
Year 10 BC was either a common year starting on Tuesday, Wednesday or Thursday or a leap year starting on Tuesday or Wednesday of the Julian calendar and a common year starting on Sunday of the Proleptic Julian calendar. At the time, it was known as the Year of the Consulship of Maximus and Antonius. The denomination 10 BC for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.
Year 21 BC was either a common year starting on Monday, Tuesday or Wednesday or a leap year starting on Tuesday of the Julian calendar and a leap year starting on Sunday of the Proleptic Julian calendar. At the time, it was known as the Year of the Consulship of Lollius and Lepidus. The denomination 21 BC for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.
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.
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.
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 P'ent'ay Churches. The Ethiopian calendar 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:
The Holocene calendar, also known as the Holocene Era or Human Era (HE), is a year numbering system that adds exactly 10,000 years to the currently dominant numbering scheme, placing its first year near the beginning of the Holocene geological epoch and the Neolithic Revolution, when humans transitioned from a hunter-gatherer lifestyle to agriculture and fixed settlements. The current year by the Gregorian calendar, AD 2019 is 12019 HE in the Holocene calendar. The HE scheme was first proposed by Cesare Emiliani in 1993.
Year zero does not exist in the Anno Domini (AD) 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.
The tables below list equivalent dates in the Julian and Gregorian calendars. Years are given in astronomical year numbering.