Anno Domini (AD or A.D.) and Before Christ (BC or B.C.) are designations used to label or number years used with the Julian and Gregorian calendars. The term Anno Domini is Medieval Latin, translated as In the year of the Lord, and as in the year of Our Lord.:782 It is sometimes specified more fully as Anno Domini Nostri Iesu (Jesu) Christi ("In the Year of Our Lord Jesus Christ"). This calendar era is based on the traditionally reckoned year of the conception or birth of Jesus of Nazareth, with AD counting years from the start of this epoch, and BC denoting years before the start of the era. There is no year zero in this scheme, so the year AD 1 immediately follows the year 1 BC. This dating system was devised in 525, but was not widely used until after 800.
The Gregorian calendar is the most widely used calendar in the world today. For decades, it has been the unofficial global standard, adopted for pragmatic interests of international communication, transportation, and commercial integration, and recognized by international institutions such as the United Nations and the Universal Postal Union.
Traditionally, English followed Latin usage by placing the abbreviation before the year number for AD. Since BC is not derived from Latin it is placed after the year number (for example: AD 2014, but 68 BC). However, placing the AD after the year number (as in "2014 AD") is also becoming common usage. The abbreviation is also widely used after the number of a century or millennium, as in "fourth century AD" or "second millennium AD" (although conservative usage formerly rejected such expressions). Because BC is the English abbreviation for Before Christ, it is sometimes incorrectly concluded that AD means After Death, i.e., after the death of Jesus. However this would mean that the ~33 years commonly associated with the life of Jesus would not be present in either BC or AD time scales.
Terminology that is viewed by some as being more neutral and inclusive of non-Christian peoples is to call this the Christian, Current, or Common Era (abbreviated as CE or C.E.), with the preceding years referred to as Before the Common, Christian, or Current Era (BCE or B.C.E.). Astronomical year numbering and ISO 8601 avoid words or abbreviations related to Christianity, but use the same numbers for years AD.
The Anno Domini dating system was devised in 525 by Dionysius Exiguus to enumerate the years in his Easter table. His system was to replace the Diocletian era that had been used in an old Easter table because he did not wish to continue the memory of a tyrant who persecuted Christians. The last year of the old table, Diocletian 247, was immediately followed by the first year of his table, AD 532. When he devised his table, Julian calendar years were identified by naming the consuls who held office that year—he himself stated that the "present year" was "the consulship of Probus Junior", which was 525 years "since the incarnation of our Lord Jesus Christ". Thus Dionysius implied that Jesus' Incarnation occurred 525 years earlier, without stating the specific year during which his birth or conception occurred. "However, nowhere in his exposition of his table does Dionysius relate his epoch to any other dating system, whether consulate, Olympiad, year of the world, or regnal year of Augustus; much less does he explain or justify the underlying date.":778
- In modern times Incarnation is synonymous with the conception, but some ancient writers, such as Bede, considered Incarnation to be synonymous with the Nativity
- The civil, or consular year began on 1 January but the Diocletian year began on 29 August
- There were inaccuracies in the list of consuls
- There were confused summations of emperors' regnal years
It has also been speculated by Georges Declercq that Dionysius' desire to replace Diocletian years with a calendar based on the incarnation of Christ was to prevent people from believing the imminent end of the world. At the time it was believed that the Resurrection and end of the world would occur 500 years after the birth of Jesus. The old Anno Mundi calendar theoretically commenced with the creation of the world based on information in the Old Testament. It was believed that based on the Anno Mundi calendar Jesus was born in the year 5500 (or 5500 years after the world was created) with the year 6000 of the Anno Mundi calendar marking the end of the world. Anno Mundi 6000 (approximately AD 500) was thus equated with the resurrection of Christ and the end of the world  but this date had already passed in the time of Dionysius. Dionysius therefore searched for a new end of the world at a later date. He was heavily influenced by ancient cosmology, in particular the doctrine of the Great Year that places a strong emphasis on planetary conjunctions. Dionysius decided that when all the planets were in conjunction this cosmic event would mark the end of the world. Dionysius accurately calculated that this conjunction would occur in May AD 2000, about 1500 years after the life of Dionysius. Dionysius then applied another cosmological timing mechanism based on precession of the equinoxes (that had only been discovered about six centuries earlier). Though incorrect, many people at the time believed that the precessional cycle was 24,000 years which included twelve astrological ages of 2,000 years each. Dionysius believed that if the planetary alignment of May 2000 marked the end of an age, then the birth of Jesus Christ marked the beginning of the age 2,000 years earlier on the 23rd March (the date of the Northern Hemisphere Spring Equinox and beginning of many yearly calendars from ancient times). He therefore deducted 2,000 years from the May 2000 conjunction to produce AD 1 for the incarnation of Christ even though modern scholars and the Roman Catholic Church acknowledge that the birth of Jesus was a few years earlier than AD 1.
The Anglo-Saxon historian the Venerable Bede, who was familiar with the work of Dionysius Exiguus, used Anno Domini dating in his Ecclesiastical History of the English People, finished in 731. In this same history he also used another Latin term, "ante vero incarnationis dominicae tempus" ("the time before the Lord's true incarnation"), equivalent to the English "before Christ", to identify years before the first year of this era, thus establishing the standard of not using a year zero, even though he used zero in his computus. Both Dionysius and Bede regarded Anno Domini as beginning at the incarnation of Jesus, but "the distinction between Incarnation and Nativity was not drawn until the late 9th century, when in some places the Incarnation epoch was identified with Christ's conception, i.e., the Annunciation on March 25" (Annunciation style).:881
On the continent of Europe, Anno Domini was introduced as the era of choice of the Carolingian Renaissance by Alcuin. Its endorsement by Emperor Charlemagne and his successors popularizing the usage of the epoch and spreading it throughout the Carolingian Empire ultimately lies at the core of the system's prevalence. According to the Catholic Encyclopedia, popes continued to date documents according to regnal years for some time, but usage of AD gradually became more common in Roman Catholic countries from the 11th to the 14th centuries. In 1422, Portugal became the last Western European country to switch to the system begun by Dionysius. Eastern Orthodox countries only began to adopt AD instead of the Byzantine calendar in 1700 when Russia did so, with others adopting it in the 19th and 20th centuries.
Even though Anno Domini was in widespread use by the 9th century, Before Christ (or its equivalent) did not become common until much later. Bede used the expression "anno igitur ante incarnationem Dominicam" (before the Incarnation of the Lord) twice. "Anno an xpi nativitate" (before the birth of Christ) is found in 1474 in a work by a German monk. In 1627, the French Jesuit theologian Denis Pétau (Dionysius Petavius in Latin), with his work De doctrina temporum, popularized the usage ante Christum (Latin for "Before Christ") to mark years prior to AD.
Change of year
When the reckoning from Jesus' incarnation started replacing the previous dating systems in western Europe, different people chose different Christian feast days to begin the year: Christmas, Annunciation, or Easter. Thus, depending on the time and place, year number changed on different days, which created slightly different styles in chronology:
- from 25 March 753 AUC (today in 1 BC), i.e. from the incarnation of Jesus. That first "Annunciation style" appeared in Arles at the end of the 9th century then spread to Burgundy and northern Italy. It was not commonly used and was called "calculus pisanus" since it was adopted in Pisa and survived there till 1750.
- from 25 December 753 AUC (today in 1 BC), i.e. from the birth of Jesus. It was called "Nativity style" and had been spread by the Venerable Bede together with the Anno Domini in the early Middle Ages. That reckoning of the year of Grace from Christmas was used in France, England and most of western Europe (except Spain) till the 12th century (when it was replaced by Annunciation style), and in Germany till the second quarter of the 13th century.
- from 25 March 754 AUC (today in AD 1). That second "Annunciation style" may have originated in Fleury Abbey in the early 11th century but it was spread by the Cistercians. Florence adopted that style in opposition to the one of Pisa, so it got the name of "calculus florentinus". It soon spread in France and also in England where it became common in the late 12th century and lasted until 1751.
- from Easter, starting in 754 AUC (AD 1). That "mos gallicanus" bound to a movable feast was introduced in France by king Philip Augustus (1165–1180–1223), maybe to establish a new style in the provinces reconquered from England. However, it never spread beyond the ruling élite.
With these various styles, the same day could, in some cases, be dated in 1099, 1100 or 1101. The Annunciation style also caused a major problem: in some years, there was no Easter, and in other years, that feast was celebrated twice; for example, Easter occurred on 23 March 1504 (i.e. in 1505 for us) and on 12 April 1506, but not in 1505.
Historical birth date of Jesus
Most scholars generally assume the year of the birth of Jesus to be around 6–4 BC, though some widen the range to 7–2 Before Christ (was born), but there is no definitive dating.
According to Matthew 2:1 King Herod the Great was alive when Jesus was born, and Matthew 2:16, says Herod ordered the Massacre of the Innocents in response to Jesus' birth. Blackburn and Holford-Strevens fix King Herod's death shortly before Passover in 4 BC:770, and say that those who accept the story of the Massacre of the Innocents sometimes associate the star that led the Biblical Magi with the planetary conjunction of 15 September 7 BC or Halley's comet of 12 BC (less likely since comets were usually considered bad omens); even historians who do not accept the Massacre accept the birth under Herod as a tradition older than the written gospels.:776
The Gospel of Luke states that Jesus was conceived during the reign of Herod the Great[Luke 1:5-38] (i.e., before 4 BC) while also stating that Jesus was born when Cyrenius (or Quirinius) was the governor of Syria and carried out the census of the Roman provinces of Syria and Iudaea.[Luke 2:1-3] The Jewish historian Josephus, in his Antiquities of the Jews (ca. AD 93), indicates that Cyrenius/Quirinius' governorship of Syria began in AD 6, and that the census occurred sometime between AD 6–7, which is incompatible with a conception prior to 4 BC. On this point, Blackburn and Holford-Strevens state that "St. Luke raises greater difficulty ... Most critics therefore discard Luke".
The Gospel of Luke also states that Jesus was "about thirty years old" [Luke 3:23] during the 15th year of the reign of Tiberius Caesar [Luke 3:1]. Tiberius began his reign as Caesar in September of AD 14. The 15th year of his reign would then be AD 28 or 29. If Jesus was born in 5 or 4 BC, that would put the start of Jesus' ministry around age 32 to 34. Most scholars do not see this as a contradiction of Luke's claim that Jesus was "about thirty years old." Some scholars rely on John 8:57: "thou are not yet fifty years old", making the earliest possible year for Jesus's birth c. 18 BC.:776
During the first six centuries of what would come to be known as the Christian era, European countries used various systems to count years. Systems in use included consular dating, imperial regnal year dating, and Creation dating.
Although the last non-imperial consul, Basilius, was appointed in 541 by Emperor Justinian I, later emperors through Constans II (641–668) were appointed consuls on the first 1 January after their accession. All of these emperors, except Justinian, used imperial post-consular years for all of the years of their reign alongside their regnal years. Long unused, this practice was not formally abolished until Novell XCIV of the law code of Leo VI did so in 888.
Another calculation had been developed by the Alexandrian monk Annianus around the year AD 400, placing the Annunciation on 25 March AD 9 (Julian)—eight to ten years after the date that Dionysius was to imply. Although this Incarnation was popular during the early centuries of the Byzantine Empire, years numbered from it, an Era of Incarnation, were only used, and are still only used, in Ethiopia, accounting for the eight- or seven-year discrepancy between the Gregorian and the Ethiopian calendars. Byzantine chroniclers like Maximus the Confessor, George Syncellus, and Theophanes dated their years from Annianus' creation of the World. This era, called Anno Mundi, "year of the world" (abbreviated AM), by modern scholars, began its first year on 25 March 5492 BC. Later Byzantine chroniclers used Anno Mundi years from 1 September 5509 BC, the Byzantine Era. No single Anno Mundi epoch was dominant throughout the Christian world. Eusebius of Caesarea in his Chronicle used an era beginning with the birth of Abraham, dated in 2016 BC (AD 1 = 2017 Anno Abrahami).
Spain and Portugal continued to date by the Era of the Caesars or Spanish Era, which began counting from 38 BC, well into the Middle Ages. In 1422, Portugal became the last Catholic country to adopt the Anno Domini system.
The Era of Martyrs, which numbered years from the accession of Diocletian in 284, who launched the last yet most severe persecution of Christians, was used by the Church of Alexandria, and is still used officially by the Coptic church. It also used to be used by the Ethiopian church. Another system was to date from the crucifixion of Jesus Christ, which as early as Hippolytus and Tertullian was believed to have occurred in the consulate of the Gemini (AD 29), which appears in the occasional medieval manuscript.
CE and BCE
Alternative names for the Anno Domini era include vulgaris aerae (found 1615 in Latin), "Vulgar Era" (in English, as early as 1635), "Christian Era" (in English, in 1652), "Common Era" (in English, 1708), and "Current Era". Since 1856, the alternative abbreviations CE and BCE are sometimes used in place of AD and BC.
Anno Domini is sometimes referred to as the Common Era, Christian Era, or Current Era (abbreviated as C.E. or CE). CE is often preferred by those who desire a term that does not explicitly use religious titles. For example, Cunningham and Starr (1998) write that "B.C.E./C.E. …do not presuppose faith in Christ and hence are more appropriate for interfaith dialog than the conventional B.C./A.D." Upon its foundation, the Republic of China adopted the Minguo Era, but used the Western calendar for international purposes. The translated term was 西元 ("Western Era"). Later, in 1949, the People's Republic of China adopted 公元 (gōngyuán, "Common Era") for all purposes domestic and foreign.
No year zero
In the AD year numbering system, whether applied to the Julian or Gregorian calendars, AD 1 is preceded by 1 BC. There is no year "0" between them. Because of this, most experts agree that a new century begins in a year with the last digits being "01" (1801, 1901, 2001); new millennia likewise began in 1001 and 2001. A common misconception is that centuries and millennia begin when the trailing digits are zeroes (1800, 1900, 2000, etc.); moreover, this convention was widely used to celebrate the new millennium in the year 2000. For computational reasons astronomical year numbering and the ISO 8601 standard designate years so that AD 1 = year 1, 1 BC = year 0, 2 BC = year −1, etc. In common use, ancient dates are expressed in the Julian calendar, but ISO 8601 uses the Gregorian calendar and astronomers may use a variety of time scales depending on the application. Thus dates using the year 0 or negative years may require further investigation before being converted to BC or AD.
- Human Era
- International Fixed Calendar (also called the International Perpetual calendar)
- Leap week calendars
- World Calendar
- World Season Calendar
Notes and references
- "Anno Domini". Merriam Webster Online Dictionary. Merriam-Webster. 2003. Retrieved 2011-10-04. "Etymology: Medieval Latin, in the year of the Lord"
- "Online Etymology Dictionary". Retrieved 2011-10-04.
- Blackburn & Holford-Strevens 2003, p. 782 "since AD stands for anno Domini, 'in the year of (Our) Lord'."
- Teresi, Dick (July 1997). "Zero". The Atlantic.
- Eastman, Allan. "A Month of Sundays". Date and Time. Archived from the original on 2010-05-06. Retrieved 2010-05-04.
- This convention comes from grammatical usage. Anno 500 means "in the year 500"; anno domini 500 means "in the year 500 of Our Lord". Just as "500 in the year" is not good English syntax, neither is 500 AD; whereas "AD 500" preserves syntactic order when translated.
- Chicago Manual of Style, 1993, p. 304.
- Donald P. Ryan, (2000), 15.
- Dunn, James DG (2003). Jesus Remembered. Eerdmans Publishing. p. 324.
- Paul L. Maier "The Date of the Nativity and Chronology of Jesus" in Chronos, kairos, Christos: nativity and chronological studies by Jerry Vardaman, Edwin M. Yamauchi 1989 ISBN 0-931464-50-1 pp. 113–129
- New Testament History by Richard L. Niswonger 1992 ISBN 0-310-31201-9 pp. 121–124
- The Cradle, the Cross, and the Crown: An Introduction to the New Testament by Andreas J. Köstenberger, L. Scott Kellum 2009 ISBN 978-0-8054-4365-3 p. 114
- Christianity and the Roman Empire: background texts by Ralph Martin Novak 2001 ISBN 1-56338-347-0 pp. 302–303
- Blackburn & Holford-Strevens 2003, 767
- Nineteen year cycle of Dionysius Introduction and First Argumentum.
- Blackburn & Holford-Strevens 2003
- Declercq, Georges, "Anno Domini. The Origins of the Christian Era" Turnhout, Belgium, 2000
- Wallraff, Martin: Julius Africanus und die Christliche Weltchronik. Walter de Gruyter, 2006
- Mosshammer, Alden A.: The Easter Computus and the Origins of the Christian Era. Oxford University Press, 2009, p. 254, p. 270, p. 328
- Declercq, Georges: Anno Domini. The Origins of the Christian Era. Turnhout Belgium. 2000
- Consideration of the Origin of the Yearly Count in the Julian and Gregorian Calendars. Cosmology Through Time. Ancient and Modern Cosmologies in the Mediterranean Area. G. Giobbi S. Colafrancesco (Editor). Mimesis, 2004 (http://www.calendersign.com/en/to_adjustment_AD.php)
- Consideration of the Origin of the Yearly Count in the Julian and Gregorian Calendars. Cosmology Through Time. Ancient and Modern Cosmologies in the Mediterranean Area. G. Giobbi S. Colafrancesco (Editor). Mimesis, 2004
- The Cosmological Circumstances and Results of the Anno Domini Invention: Anno Mundi 6000, Great Year, Precession, End of the World Calculations. Astronomy and Civilization in the New Enlightenment:
- Astronomical Phenomena that Influenced the Compilation of Anno Domini. The Inspiration of Astronomical Phenomena. Volume 441.
- The Last Day Calculation of Anno Domini. Proceedings of the SEAC conference Ljubljana 2012. To be published in Anthropological Notebooks, official journal of the Slovene Anthropological Society. 2013
- Bede 731, Book 1, Chapter 2, first sentence.
- Compare Bede 731, Book 1, Chapter 2, first sentence, with Chapter 3.
- Gerard, 1908
- "General Chronology". New Advent Catholic Encyclopedia. Vol III. Robert Appleton Company, New York. 1908. Retrieved 2011-10-25.
- Werner Rolevinck in Fasciculus temporum (1474) used Anno an xpi nativitatem (in the year before the birth of Christ) for all years between creation and Jesus. "xpi" is the Greek χρι in Latin letters, which is a cryptic abbreviation for christi. This phrase appears upside down in the centre of recto folios (right hand pages). From Jesus to Pope Sixtus IV he usually used Anno christi or its cryptic form Anno xpi (on verso folios—left hand pages). He used Anno mundi alongside all of these terms for all years.
- Steel, Duncan (2000). Marking time: the epic quest to invent the perfect calendar. p. 114. ISBN 978-0-471-29827-4. Retrieved 2010-06-01.
- Hunt, Lynn Avery (2008). Measuring time, making history. p. 33. ISBN 978-963-9776-14-2. Retrieved 2010-06-01.
- Petau, Denis (1758). search for "ante Christum" in a 1748 reprint of a 1633 abridgement entitled Rationarium temporum by Denis Petau. Retrieved 2010-06-01.
- C.R. Cheney, A Handbook of Dates, for students of British history, Cambridge University Press, 1945–2000, pp. 8–14.
- Easter Sunday/Jewish Passover calculator
- Some of the historians and Biblical scholars who place the birth and death of Jesus within this range include D. A. Carson, Douglas J. Moo and Leon Morris. An Introduction to the New Testament. Grand Rapids, MI: Zondervan Publishing House, 1992, 54, 56
- Michael Grant, Jesus: An Historian's Review of the Gospels, Scribner's, 1977, p. 71.
- Ben Witherington III, "Primary Sources," Christian History 17 (1998) No. 3:12–20.
- Doggett 1992, p579: "Although scholars generally believe that Christ was born some years before AD 1, the historical evidence is too sketchy to allow a definitive dating".
- Matthew 2:1
- Matthew 2:16
- Flavius Josephus. The Antiquities of the Jews, Book 18, Chapters 1–2. Josephus indicates that the census under Cyrenius (i.e., Quirinius) occurred in the 37th year after Octavian's (i.e., Gaius Julius Caesar Augustus') victory over Marc Antony at Actium, which secular historical records date to 2 September 31 BC. Therefore 31 BC + 37 years = AD 6–7.
- John 8:57
- Blackburn & Holford-Strevens 2003, p. 776 "Most critics therefor discard Luke; some have rehabilitated John, who seems to imply that Jesus was born c. 18 BC."
- Roger S. Bagnall and Klaas A. Worp, Chronological Systems of Byzantine Egypt, Leiden, Brill, 2004.
- Alfred von Gutschmid, Kleine Schriften, F. Ruehl, Leipzig, 1889, p.433.
- Johannes Kepler (1615). Joannis Keppleri Eclogae chronicae: ex epistolis doctissimorum aliquot virorum & suis mutuis, quibus examinantur tempora nobilissima: 1. Herodis Herodiadumque, 2. baptismi & ministerii Christi annorum non plus 2 1/4, 3. passionis, mortis et resurrectionis Dn. N. Iesu Christi, anno aerae nostrae vulgaris 31. non, ut vulgo 33., 4. belli Iudaici, quo funerata fuit cum Ierosolymis & Templo Synagoga Iudaica, sublatumque Vetus Testamentum. Inter alia & commentarius in locum Epiphanii obscurissimum de cyclo veteri Iudaeorum. (in Latin). Francofurti : Tampach. Retrieved 2011-05-18. "anno aerae nostrae vulgaris"
- Kepler, Johann; Vlacq, Adriaan (1635). Ephemerides of the Celestiall Motions, for the Yeers of the Vulgar Era 1633.... Retrieved 2011-05-18.
- Sliter, Robert (1652). A celestiall glasse, or, Ephemeris for the year of the Christian era 1652 being the bissextile or leap-year: contayning the lunations, planetary motions, configurations & ecclipses for this present year ... : with many other things very delightfull and necessary for most sorts of men: calculated exactly and composed for ... Rochester. London: Printed for the Company of Stationers.
- The History of the Works of the Learned 10. London: Printed for H. Rhodes. January 1708. p. 513. Retrieved 2011-05-18.
- BBC Team (8 February 2005). "History of Judaism 63BCE–1086CE". BBC Religion & Ethics. British Broadcasting Corporation. Archived from the original on 2011-05-13. Retrieved 2011-05-18. "Year 1: CE – What is nowadays called the 'Current Era' traditionally begins with the birth of a Jewish teacher called Jesus. His followers came to believe he was the promised Messiah and later split away from Judaism to found Christianity"
- Raphall, Morris Jacob (1856). Post-Biblical History of The Jews. Moss & Brother. Archived from the original on 2011-05-11. Retrieved 2011-05-18. The term common era does not appear in this book; the term Christian era [lowercase] does appear a number of times. Nowhere in the book is the abbreviation explained or expanded directly.
- Robinson, B.A. (20 April 2009). "Justification of the use of "CE" & "BCE" to identify dates. Trends". ReligiousTolerance.org.
- William Safire (17 August 1997). "On Language: B.C./A.D. or B.C.E./C.E.?". The New York Times Magazine.
- Cunningham, ed. by Philip A. (2004). Pondering the Passion : what's at stake for Christians and Jews?. Lanham, Md. [u.a.]: Rowman & Littlefield. p. 193. ISBN 978-0742532182.
- To convert from a year BC to astronomical year numbering, reduce the absolute value of the year by 1, and prefix it with a negative sign (unless the result is zero). For years AD, omit the AD and prefix the number with a plus sign (plus sign is optional if it is clear from the context that the year is after the year 0). [Doggett, 1992, p. 579]
- Abate, Frank R(ed.) (1997). Oxford Pocket Dictionary and Thesaurus (American ed.). New York: Oxford University Press. ISBN 0-19-513097-9.
- Bede. (731). Historiam ecclesiasticam gentis Anglorum. Accessed 2007-12-07.
- Chicago Manual of Style (2nd ed.). University of Chicago. 1993. ISBN 0-226-10389-7.
- Blackburn, Bonnie; Holford-Strevens, Leofranc (2003). The Oxford companion to the Year: An exploration of calendar customs and time-reckoning. Oxford University Press. ISBN 0-19-214231-3. Corrected reprinting of original 1999 edition.
- Cunningham, Philip A; Starr, Arthur F (1998). Sharing Shalom: A Process for Local Interfaith Dialogue Between Christians and Jews. Paulist Press. ISBN 0-8091-3835-2.
- Declercq, Georges (2000). Anno Domini: The origins of the Christian era. Turnhout: Brepols. ISBN 2-503-51050-7. (despite beginning with 2, it is English)
- Declercq, G. "Dionysius Exiguus and the Introduction of the Christian Era". Sacris Erudiri 41 (2002): 165–246. An annotated version of part of Anno Domini.
- Doggett. (1992). "Calendars" (Ch. 12), in P. Kenneth Seidelmann (Ed.) Explanatory supplement to the astronomical almanac. Sausalito, CA: University Science Books. ISBN 0-935702-68-7.
- Gerard, J. (1908). "General Chronology". In The Catholic Encyclopedia. New York: Robert Appleton Company. Retrieved 2008-07-16 from New Advent: http://www.newadvent.org/cathen/03738a.htm
- Richards, E. G. (2000). Mapping Time. Oxford: Oxford University Press. ISBN 0-19-286205-7.
- Riggs, John (January 2003). "Whatever happened to B.C. and A.D., and why?". United Church News. Retrieved 2005-12-19.
- Ryan, Donald P. (2000). The Complete Idiot's Guide to Biblical Mysteries. Alpha Books. p. 15. ISBN 0-02-863831-X.
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