Difference Between AD and BC

In the Julian and Gregorian calendars, the phrases anno Domini (AD) and before Christ (BC) are used to designate or number years. The phrase "anno Domini nostri Jesu Christi" translates to "in the year of our Lord Jesus Christ" and is derived from the complete original phrase "anno Domini nostri Jesu Christi," which literally means "in the year of our Lord Jesus Christ".

This conventionally reckoned year of Jesus' conception or birth, with AD signifying years from the beginning of this epoch and BC denoting years before the beginning of the era is on which the calendar period is based. In this arrangement, there is no year zero; consequently, the year AD 1 immediately succeeds the year 1 BC. Dionysius Exiguus of Scythia Minor invented this date method around 525, although it was not extensively utilized until the 9th century. 

Let us take a look at the origin and get to know more details on what is the difference between AD and BC.

Origin of A.D. and B.C.

The concept of counting years has been for as long as written records have existed, but the concept of synchronizing where everyone begins counting is very recent. The international practice now is to identify years based on a conventional estimate of the year Jesus was born — the "A.D." and "B.C." systems. The abbreviation "A.D." stands for anno domini, Latin for "in the year of the Lord," and alludes to the birth of Jesus Christ. "B.C." is an abbreviation meaning "before Christ." In English, "A.D." is commonly used before the year, thus "A.D. 2014" would be translated as "in the year of our lord 2014." 

In recent years, a new interpretation of B.C./A.D. has gained momentum. Many publications use the abbreviation "C.E." for "common era," and "B.C.E." for "before the common era." Let's start with some historical context before delving into how and why the system was created. Dionysius, named after Rome's 51st emperor, who reigned from A.D. 284 to A.D. 305 developed his system to replace the Diocletian system. Dionysius' Easter table began with the year "Anno Domini 532," which was followed by the year "Anno Diocletiani 247." Dionysius made the modification intentionally to erase the memory of this cruel persecution of Christians.

Dionysius never stated how he calculated the date of Jesus' birth, but some writers believe he utilized contemporary views about cosmology, planetary conjunctions, and the precession of equinoxes. Dionysius sought to establish A.D. 1 as the year of Jesus Christ's birth, but he was a few years off, which is why the best contemporary estimations place Christ's birth at 4 B.C.

The B.C. component was added two centuries after Dionysius, in 731, when the Venerable Bede of Northumbria wrote his "Ecclesiastical History of the English People." Dionysius' method has been widely utilized up to this time. Bede's work not only drew the A.D. system to the notice of other academics but also enlarged the system to cover years prior to A.D. 1. Dionysius sought to designate A.D. 1 as the year of Jesus Christ's birth, but he was wrong by a few years, which is why the best contemporary estimations place Christ's birth at 4 B.C.

How did AD and BC Come into Use?

After Holy Roman Emperor Charlemagne adopted the B.C./A.D. method for marking acts of governance throughout Europe in the ninth century, the system gained popularity. By the 15th century, the B.C./A.D. the system had been established throughout Western Europe. The system was inherent in the Gregorian calendar's introduction in the 16th century, and it later became an international standard in 1988, which was specified as an internationally accepted way of expressing dates and times, the International Organization for Standardization issued ISO 8601. In the late eighth century, the English clergyman and scholar Alcuin established Anno Domini as the period of choice for the Carolingian Renaissance on the continent of Europe. Its acceptance by Emperor Charlemagne and his successors, who popularized and extended the epoch across the Carolingian Empire, is ultimately at the heart of the system's popularity. 

According to the Catholic Encyclopedia, popes continued to use regnal years to date documents for some time, but from the 11th through the 14th centuries, the usage of AD became increasingly prevalent in Catholic countries. Portugal was the final Western European country to adopt Dionysius' method in 1422. Eastern Orthodox countries first began to use the AD calendar instead of the Byzantine calendar in 1700, when Russia did so, with others following suit in the nineteenth and twentieth centuries.

What is the Common Era?

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Image: Difference between BC and AD

The Common Period (CE) is one of the year notations used for the Gregorian calendar (and its predecessor, the Julian calendar), the world's most widely used calendar period. Before the Common Era (BCE) is the period preceding the Common Era (CE). BCE and CE are alternate notations for Dionysian BC and AD, respectively. The Dionysian era differentiates between eras by using the notations BC ("Before Christ") and AD ("After Christ") (Latin: Anno Domini, in [the] year of Lord). The two notation methods are numerically equivalent: "2021 CE" and "AD 2021" represent the present year, but "400 BCE" and "400 BC" both describe the same year. The Gregorian calendar is still widely used today and serves as an international standard for civil calendars. 

The term dates back to 1615, when it first appeared in a book by Johannes Kepler as annus aerae nostrae vulgaris (year of our common era), and to 1635 in English as "Vulgar Era."  The phrase "Common Era" first appeared in English in 1708, and was popularized by Jewish religious academics in the mid-nineteenth century.

We have seen the main difference between AD and BC in this article. The calendar period after the birth of Jesus Christ is denoted by the abbreviation AD. The year of Christ's birth is generally referred to as AD 1, and the year before is referred to as 1 BC. This calendaring system was developed around AD 525, although it was not generally adopted until AD 800. CE, which stands for Common Era, Christian Era, or Current Era, is an alternative to AD. There has been a campaign to replace the B.C. and A.D. designations with B.C.E and C.E., which stand for “before common era” and “common era,” respectively. The distinction is purely semantic—that is, AD 100 is the same as CE 100; the only difference is the name.