1. The point of time, usually marked by some important event, from which a series of year's, termed an era, is computed or dated; although "epoch" and "aera" are often used synonymously for either a chronological period or date in general (see Penny Cyclopedia, s.v. AEra). An aera properly so called the ancient Hebrews did not possess. Signal events seem to have been made use of as points from which to date. Moses, like Herodotus, reckoned by generations. The Exodus, as may be seen in Ex 19:1, and Nu 33:38, probably, also, the building of the first Temple (1Ki 9:10; 2Ch 3:2), were employed as starting-points to aid in assigning events their position in historical succession. Also the destruction of the first Temple, or the beginning of the Babylonish captivity (in the summer of the year B.C. 586), and the liberation of the Jews from the Syrian yoke by the valor of the Maccabees (in the autumn of the year B.C. 143), were used as epochs from which time was reckoned. After the manner of other nations, the Hebrews computed time by the succession of their princes, as may be seen throughout the books of Kings and Chronicles. At a later period, and in the first book of the Maccabees, what is termed the Greek sera, or that of the Seleucidae, began to be employed. This aera, which is also called the aera of the Syro-Macedonians, commences from the year of Rome 442, twelve years after the death of Alexander, and 311 years and four months before the birth of our Savior, the epoch of the first conquest of Seleucus Nicator in that part of the West which afterwards composed the immense empire of Syria (see Noris, Annus et epocha Syro-Macedonum, Lips. 1696). The Julian year, formed of the Roman months, to which Syrian names were given, was used. The aera prevailed not only in the dominions of Seleucus, but among almost all the people of the Levant, where it still exists. The Jews did not abandon the use of this sera until within the last 400 years. At present they date from the Creation, which they hold to have taken place 3760 years and three months before the commencement of the Christian aera. In order to fix their new moons and years; as well as their feasts and festivals, they were obliged to make use of astronomical calculations and cycles. The first cycle they used for this purpose was one of 84 years, but this being discovered to be faulty, they had recourse to: the Metonic cycle of 19 years, which was established by the authority of rabbi Hillel, prince of the Sanhedrim, about the year 360 of the Christian aera. This they still use, and say it is to be observed till the coming of the Messiah. Indeed, some contend that their present practice of dating from the Creation of the world is of great antiquity. Their year is luni-solar, consisting either of 12 or 13 months each, and each month of 29 or 30 days; for in the compass of the Metonic cycle there are 12 common years, consisting of 12 months, and seven intercalary years, consisting of 13 months, which are the third, sixth, eighth, eleventh, fourteenth, seventeenth, and nineteenth of the cycle. SEE CHRONOLOGY.
The birth of the Savior of the world probably took place somewhat earlier than the date which is usually assigned to it. Usage, however, has long fixed the aera to which it gave rise, namely, the Christian aera, or the sera of the Incarnation, to begin on the 10th day of January, in the middle of the fourth year of the 194th Olympiad, the 753d year of the building of Rome, and in the 4714th of the Julian period. The use of the Christian aera was introduced in the sixth century; in France it was first employed in the seventh. About the eighth it was generally adopted; but considerable difference has existed not only in various countries, but even in the same place in the same country and at the same period, respecting the commencement of the year. Nor did the use of the sera become universal in Christendom till the fifteenth century. The Christian year consists of 365 days for three successive years, and of 366 in the fourth, which is termed leap-year. This computation subsisted for 1000 years without alteration, and is still used by the Greek Church. The simplicity of this form has brought it into very general use, and it is customary for astronomers and chronologists, in treating of ancient times, to date back in the same order from its commencement. There is, unfortunately, a little ambiguity on this head, some persons reckoning the year immediately before the birth of Christ as 1 B.C., and others noting it with 0, and the second year before Christ with 1, thus producing one year less than those who use the former notation. The first, however, is the usual mode. The Christian year, arranged as has been shown, was 11' 11" too long, an error which amounted to a day in nearly 129 years. Towards the end of the sixteenth century the time of celebrating the Church festivals had advanced ten days beyond the periods fixed by the Council of Nice in 325. It was, in consequence, ordered by a bull of Gregory XIII that the year 1582 should consist of only 355 days, which was brought about by omitting ten days in the month of October, namely, from the 5th to the 14th. And to prevent the recurrence of a like irregularity, it was also ordered that in three centuries out of four the last year should be a common instead of a leap-year, as it would have been by the Julian Calendar. The year 1600 remained a leap- year, but 1700, 1800, and 1900 were to be common years. This amended mode of computing was called "The New Style." It was immediately adopted in all Catholic countries, but Protestants came to use it only gradually. In England the reformed calendar was adopted in the year 1752 by omitting eleven days, to which the difference between the styles then amounted. The alteration was effected in the month of September, the day which would have been the third being called the fourteenth. SEE VULGAR AERA.
The following summary shows the correspondence of the principal epochs, aeras, and periods with that of the birth of Christ, or Christian aera. (A valuable treatise on AEras of ancient and modern Times may be found in the Companion to the Almanac, 1830.) SEE AERA.
2. The term epoch is used by modern writers to denote "critical junctures in the development of history, the signals of a new creation; hence termed ἐποχαί, pauses or resting-places for contemplation. What exists at the epoch in the germ is developed to a more advanced stage, and thus afterwards becomes the Period. The former denotes the fountain-head, the latter the stream; their limits are where a new form of culture again appears in an epoch. The epochs are either critical and destructive, or creative and organizing." — Neander, Hist. of Dogmas, 1:20.