Millennium << muh LEHN ee uhm >>, in science, is any period of 1,000 years. The term is often used to refer to periods before or after the birth of Christ. The year of Christ’s birth is traditionally recognized as A.D. 1. The letters A.D. are the abbreviation for anno Domini, which is Latin for in the year of our Lord. Thus, the first millennium since the birth of Christ was the period from A.D. 1 through A.D. 1000. According to this manner of reckoning, the years of the second millennium would be A.D. 1001 through 2000, and the third millennium would have begun on Jan. 1, 2001.
Some people mistakenly believe that the third millennium since the birth of Christ began on Jan. 1, 2000. This error is easy to understand. It seems logical that a millennium would begin when there is a change in the first digit of the number of the year—for example, when the 1 of 1999 changes to the 2 of 2000. A millennium actually does begin on Jan. 1, 2000—but it is not the third millennium since the birth of Christ. Rather, it is the millennium of all years after Christ’s birth having four digits beginning with “2.” Because a millennium is any period of 1,000 years, one can reckon a millennium from any starting date.
See also Calendar.
