Who originated the terms B.C. and A.D. for calendar purposes.?
535270
B.C. Stands for before christ. The actual birth of Jesus is placed around 33 BC. \n\nA.D. Stand for Anno Domini which is latin for the year of our Lord and means the number of years since the birth of Christ. It is sometimes mistaken to mean After Death, the years after Jesus died.\n\nB.C.E. is often used in the place of B.C. It means Before Common Era and is used to avoid christian references.\n\nC.E. is often used in the place of A.D. It means Common Era and  like BCE is used to avoid christian references.
293074
calendar system (were astronomers and mathematician)\ntabacco, (pipes and cigars)\ngum (fron ceiba tree)\nsneakers (used them for hunting-were made out of gummy syrup),\nwriting system (debated)
17260
The hour was originally defined in ancient civilisations (including those of Egypt, Sumeria, India and China) as either one twelfth of the time between sunrise and sunset or one twenty-fourth of a full day. In either case the division reflected the widespread use of a duodecimal numbering system (counting with each thumb the spaces between the joints of the other finger on the same hand, i.e. 3 x 4 = 12) and the equally widespread tendency to make analogies among sets of data (12 months, 12 zodiacal signs, 12 main compass points, 12 hours, a dozen).
978766
All I lnow of is B.C. ("Before Christ") and A.D. ("Anno Domini" which, in Latin means "In the year of the Lord).
107215
I believe the "ancients" that the above is refering to are the Greeks.  The Romans, more specifically Julius Cesar, instigated using the calander we use today, but borrowed the names of the moon phases from the Greeks when they conquered them.
853845
The Anno Domini (B.C. and A.D) system was developed by a monk named Dionysius Exiguus (born in Scythia Minor) in Rome in 525, as an outcome of his work on calculating the date of Easter. \n\nEarly Christians designated the year via a combination of consular dating, imperial regnal year dating, and Creation dating. Use of consular dating ended when the emperor Justinian I discontinued appointing consuls in the mid sixth century, requiring the use of imperial regnal dating shortly thereafter. The last consul nominated was Anicius Faustus Albinus Basilius in 541. The papacy was in regular contact throughout the Middle Ages with envoys of the Byzantine world, and had a clear idea — sudden deaths and deposals notwithstanding — of who was the Byzantine emperor at any one time.\n\nAmong the sources of confusion mentioned by Blackburn & Holford-Strevens (2003, 778–779) are:\n\n    * In modern times Incarnation is synonymous with conception, but some ancient writers, such as Bede, considered Incarnation to be synonymous with the Nativity\n    * The civil, or consular year began on 1 January but the Diocletian year began on 29 August\n    * There were inaccuracies in the list of consuls\n    * There were confused summations of emperors' regnal years\n\nThe wikipedia link I've given you also gives citations for support each of the items I posted.
24607
Time is relative to the existence of people to care about it, and since humans were not around at the creation of the world: No answer is possible. \n\nIf you want to use Christianity in that answer, Adam and Eve didn't have a calender.
647536
C.E. today is more accepted to mean as the Common Era rather than its earlier meaning of Christian Era to make the term more universally acceptable especially to non-Christians.\n\nB.C.E. on the other hand is Before the Common Era\n\nAlthough today many resource materials still refer to the C in B.C.E. and C.E. as Christ or Christian, many groups are opting for the Common Era and Before the Common Era notations because it does not connote any religious inclination or influence. The word  Common refers to the calendar most widely used in the world today, that is the Gregorian calendar.
291816
AD: Anno Domine in the Christian era; used before dates after the supposed year Christ was born; "in AD 200" \nwordnet.princeton.edu/perl/webwn\n\nBC: Abbreviation for the term Before Christ. Years are counted back from the traditionally recognized year of Christ's birth. In academic, historical, and archaeological circles, this term is now generally replaced by Before Common Era (BCE).\nwww.archaeological.org/webinfo.php
348557
According to our calendar system Jesus was born in 4 B.C. and died in 30 A.D. at 33 years old.\nOriginally thought to be at year 1 A.D. scholars and progressing advancement in dating recalculated for the more accurate date of 4 B.C. \n\nAll these other people here have no idea what they're talking about.
622119
Although the ancient egyptions had a calendar that was divided into 12 months of 30 days, the current 12 month calendar has been in place since Feb 24, 1582.\n\nSee the page below.
286258
CE: Common Era; BCE: Before (the) Common Era.\n\nI love those.
775479
Julian dates are dates as per Julius Ceasar's calendar\nGregorian = according to Pope Gregory\nthe YYYYMMDD is only a display thing for computer systems\n\nhowever try this link for explanations and conversions\n\nhttp://www.geocities.com/atkuala/astro/cal_conversion.html
181093
Archaeologists use the term BP to mean "years Before the Present", which avoids the whole philosophical debate about AD and BC versus CE and BCE. The only trouble is, the Present, of course, changes every year. Since the BP designation was at least originally associated with radiocarbon dating, archaeologists chose the year 1950 as 'the present'. Radiocarbon dating was invented in the late 1940s, and, also, atmospheric nuclear testing was begun in the 1940s, which makes, at least the theory goes, radiocarbon dates after 1950 virtually useless, anyway. \n\nGenerally CE (for Common Era or AD) and BCE (for Before the Common Era or BC) are more acceptable.
281744
The ancient Babylonians set the numbers of hours, minutes, and seconds because their number system is based on the sexagesimal/60, so I think the Babylonians set these dates
546363
The Olympic Games were held in four year intervals, and later the Greek method of counting the years even referred to these Games, using the term Olympiad for the period between two Games. The Greeks in historical times used the Olympiads to count years, much as we today use AD and BC. "Diodorus states that there was a solar eclipse in the third year of the 117th Olympiad, which must be the eclipse of 310 BC. This gives us a date of (mid-summer) 776 for the first year of the first Olympiad". Nevertheless, there is disagreement among scholars whether the games truly began at this time or not.
349021
Because a 24 hour period is a day, it's simple to refer to the days of the week as Monday, Tuesday etc.  The first part of the name does have meaning of some sort, though I'm not sure what, I think some of this goes back to the Ancient Roman era.