Hemerologion, Ephemeris ( ἡμερολόγιον and ἐφημερίς).

The Greek year consisted of twelve months—some “full,” i.e. of 30 days each; the others, “hollow” or incomplete, of 29 days each. This made up a lunar year of 354 days, 11 days short of the solar year. To maintain some correspondence between the lunar and the solar years, and to provide at least for the festivals of the seasons always occurring at the right time of year, the Athenians early resorted to the method of intercalation. A space of time was taken which included as many days as would exactly make up eight solar years, and could easily be distributed among the same number of lunar years. This space of time was called a “great year.” Then in every third, sixth, and eighth year, a month of 29 or 30 days was inserted, so that the years in question consisted each of 383 or 384 days. This system was introduced at Athens by Solon. The period of eight years was sometimes called ἐνναετηρίς, or a period of nine years, because it began again with every ninth year; sometimes ὀκταετηρίς, or space of eight years. For this the astronomers, of whom Meton in the Periclean Age may be taken as a representative, substituted a more accurate system, which was afterwards adopted in Athens and other cities as a correction of the old calendar. This was the ἐννεακαιδεκαετηρίς of nineteen years. The alternate “full” and “hollow” months were divided into three decades, consisting of 10 or 9 days each, as the case might be. The days of the last decade were counted from more to less to correspond with the waning of the moon. Thus the 21st of the month was called the 10th of the waning moon, the 22d the 9th, the 23d the 8th, and so on. The reckoning of the year, with the order and names of the months, differed more or less in different States, the only common point being the names of the months, which were almost without exception taken from the chief festivals celebrated in them. The Athenians and the other Ionian peoples began their year with the first new moon after the summer solstice, the Dorians with the autumnal equinox, the Boeotians and other Aeolians with the winter solstice.

At the time when the Calendar Julian was adopted by the Athenians, probably about the time of the emperor Hadrian, the lunar year appears to have been changed into the solar year; and it has further been conjectured that the beginning of the year was transferred from the summer solstice to the autumnal equinox. The intercalary month was a second Poseideon inserted in the middle of the year. The official system of numbering the years differed also very much in the various States. The years received their names from the magistrates, sometimes secular, sometimes spiritual. (See Eponymus.) Historical chronology was first computed according to Olympiads, or periods of four years, beginning B.C. 776, by the historian Timaeus in the third century B.C.

The Day.—The Greeks reckoned the civil day from sunset to sunset, the Romans (like ourselves) from midnight to midnight. The natural day was reckoned by both as lasting from sunrise to sunset.