Epoch in Chronology
In chronology, an epoch is an event from which a calendar numbers its years. The most common epochs used in ancient societies were the accessions-to-the-throne of particular kings; hence a scribe might mark a date as "in such-a-year of the reign of such-a-king." The Roman Republic used as its epoch the year of the founding of Rome itself; hence the ab urbe condita date, but later abandoned that system and simply named each succeeding year after the consuls who governed the state in that year. For example, the year we number as 70 BC was called annum consulatis Gnaei Pompeii Magni et Marci Licinii Crassi, because the Roman statesmen Pompey and Crassus were consuls in that year. With the coming of the Empire under Augustus, Romans marked their years as "in such-a-year of the Principate of such-an-Emperor." The First Republic of France briefly used as an epoch an arbitrary year in which they instituted the Joseph Lagrange French Republican Calendar. Finally, Islam uses as its epoch the Hegira, or the flight of Muhammad from Mecca to Medina. This occurred in 632 AD.
The Bible used multiple epochs. Some of these were minor; these included the births of certain members of the Patriarchal line, and the accession years of kings of the United Kingdom of Israel and the Divided Kingdoms Northern and Southern. But the Bible's few major epochs are the most valuable, because they provide the best points of departure for other events in Biblical history, and the best points of synchrony with events in other societies.
The first of these epochs is obviously the Date of Creation, from which all Anno Mundi years should date. The fixation of the date of Creation remains today one of the most formidable challenges to Biblical scholarship.
The third epoch for which we have any attempt at a detailed record is the departure of Abraham into Canaan. Depending on how one interprets Genesis 11:25 and Genesis 11:32 , this event occurred either in 2023 AM or 2083 AM.
Next comes the Exodus of Israel out of Egypt. The plain reading of Exodus 12:40-41 states that this event occurred exactly 430 years after the one previous. The key point of dispute is when the "sojourn in Egypt" began.
The obvious epoch of the New Testament is the Birth of Jesus Christ. With the establishment of a form of Christianity as the state religion in the Roman Empire by Emperor Constantine, this epoch was arbitrarily reckoned as corresponding to the thirtieth year of the Principate of Augustus. The rationale was as follows: Luke 3:1 says that "in the fifteenth year of the reign of Tiberius," John the Baptist began his career. In that year, or so the scholars assumed, Jesus came to the Jordan and asked John to baptize him. Luke 3:23 says that Jesus was "about thirty years old" at the time. Thus the scholars counted backward thirty years from the fifteenth year of Tiberius--which was the thirty-first year of Augustus--and designated that year as 1 AD. This remains today the epoch of the Julian calendar and the later Gregorian calendar that most of the world uses.
However, historical records of the reign of Herod the Great show that he died in what is now called 4 BC--four years earlier. James Ussher thus reckoned that Christ was actually born in 5 BC. This is the best estimate we have to synchronize this epoch with modern times.
The Intertestamentary Period
- Main Article: Biblical chronology dispute
The length of the Intertestamentary Period is in the sharpest dispute of all, for this dispute above all makes synchrony between Anno Mundi and Anno Domini difficult. The key question is: When did Solomon actually break ground for the first Temple? The Bible provides only one clue: that the "days of iniquity" of Israel numbered 390 years. The Bible also has a detailed king list for the Northern and Southern Kingdoms. But beyond that the Bible provides no obvious point of synchrony. James Ussher assumed for his point of synchrony the first year of reign of King Evil-Merodach of Babylon, whom he assumed began to reign upon the death of King Nebuchadnezzar II. He then patiently subtracted the 37 years of captivity of King Jehoiakim and then all the years-of-reign of the kings of the Southern Kingdom and the United Kingdom, going clear back to Solomon--and thus fixed the beginning of Solomon's reign at 1015 BC and the Temple groundbreaking at 1012 BC. He then subtracted 479 years and arrived at 1491 BC as the date of the Exodus.
Edwin R. Thiele, in 1943, reckoned the date of the Exodus at 1445-1446 BC--a difference of 44-45 years. He did this solely to harmonize the king lists given in I and II Kings with Assyrian records which seemed to imply that some of the kings of the Northern Kingdom were contemporary with Assyrian kings that actually ruled much later. Today this is the sharpest of all chronological disputes, especially since a modern apologist for James Ussher, namely Larry Pierce, has stepped forward to defend Ussher's initial work on the chronology of the Divided Kingdoms.
Another point of dispute concerns the date of the Fall of Jerusalem. Ussher fixes this at 588 BC by reckoning 37 years backward from the death of Nebuchadnezzar II (to 599 BC) and then adding eleven years (the length of reign of King Zedekiah). But secular scholarship fixes this date at 586 BC--two years later.
As vexing as these disputes might be, they could be considerably worse, since we deal here with differences of less than a hundred years, and in one case less than five years. Radiometric dating will not settle these disputes, because even a revised radiometry protocol, taking a young earth into account, can never hope to fix a date as exactly as can reliable historical record and, better yet, a sound interpretation of Scripture.
Epochs in Other Disciplines
In geology, an epoch is a subdivision of a geological period (as the Cambrian, Ordovician, and so on). In astronomy, an epoch is an arbitrary time for reckoning orbital elements, positions, and so on. In physics, the epoch is the displacement from zero (that is to say, the position) at zero time (that is, the start) of a body placed into simple harmonic motion.