The Julian Period

How many days have you lived? To determine this, multiply your age by 365, add the number of days since your last birthday, and account for all leap years. Chances are your calculations will go wrong somewhere. Astronomers, however, find it convenient to express dates and time intervals in days rather than in years, months, and days. This is done by placing events within the Julian period.

The Julian period was devised in 1582 by the French classical scholar Joseph Scaliger (1540–1609) and named after his father, Julius Caesar Scaliger (1484–1558), not after the Julian calendar. Joseph Scaliger began Julian Day (JD) #1 at noon, Jan. 1, 4713 B.C., the most recent time that 3 major chronological cycles began on the same day—(1) the 28-year solar cycle, after which dates in the Julian calendar (e.g., Feb. 11) return to the same days of the week (e.g., Monday); (2) the 19-year lunar cycle, after which the phases of the moon return to the same dates of the year; and (3) the 15-year indiction cycle, used in ancient Rome to regulate taxes. It will take 7,980 years to complete the period, the product of 28, 19, and 15.

Noon of Dec. 31, 1997, marks the beginning of JD 2,450,814; that many days will have passed since the start of the Julian period. The JD at noon of any date in 1998 may be found by adding to this figure the day of the year for that date.

[Eric's note: 1998 is the year 6711 of the Julian Period, since 6,711 years have elapsed since the year 4713 B.C. The Julian Period will be completed in the year 3267, which is 1,269 years from now, and 7,980 years after 4713 B.C.]

From The World Almanac® and Book of Facts 1998, p. 313.
Copyright © 1997 by K-III Reference Corporation.

This page last revised February 18, 1999.