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Julian calendar(joo -lee-ăn) The calendar that was established in 46 bc in the Roman Empire by Julius Caesar, with Sosigenes of Alexandria as his chief advisor. It reached its final form in about 8 ad under Augustus and was in general use in the West up to 1582, when the Gregorian calendar was instituted. Each year contained 12 months and there was an average of 365.25 days per year: three years of 365 days were followed by a leap year of 366 days. (Leap years were not correctly inserted until 8 ad.) Since the average length of the year was about 11 minutes 15 seconds longer than the 365.2422 days of the tropical year, a discrepancy arose between the calendar year and the seasons, with an extra day ‘appearing’ about every 128 years.
(also Old Style), the calendar introduced by Julius Caesar in 46 B.C. The calendar fixed the length of the year as 365¼ days. (The actual length of the tropical year is 365 days, 5 hours, 48 min, and 46 sec.) This figure is obtained by inserting an additional day every four years—February 29 in the modern calendar. With the Julian calendar, the leap years are those that are evenly divisible by four, for example, 1900, 1904, 1972, and 1976. The difference between the New Style (Gregorian calendar) and Old Style amounted to 11 days in the 18th century and 12 days in the 19th century. In the 20th century, the difference amounts to 13 days. The shift from one style to the other has no effect on the day of the week.
(Old Style), a system of chronology introduced by Julius Caesar in 46 B.C. In the Julian calendar, every year that is divisible by 4, for example, 1900, 1976, and 1980, is considered a leap year; thus, the average length of a year is 365.25 days, which is 0.0078 day longer than the tropical year.
Since the error in the Julian calendar constitutes about three days every 400 years, it was replaced by the Gregorian calendar (New Style) beginning in 1582; in the USSR the Gregorian calendar was introduced February 14 (February 1 Old Style), 1918. The difference between the New and Old styles was 11 days in the 18th century and 12 days in the 19th century; in the 20th century it is 13 days. In the event of a change from one style to another, the day of the week does not change; thus, both May 1, 1979, New Style and Apr. 18, 1979, Old Style fall on Tuesday.