A century (from the Latin centum, meaning one hundred) is one hundred consecutive years. Centuries are numbered ordinally (e.g. "the seventh century AD").

Start and end in the Gregorian Calendar

According to the Gregorian calendar, the 1st century AD started on January 1, 1 and ended on December 31, 100. The 2nd century started at year 101, the third at 201, etc. The n-th century will start on the year 100×n - 99. A century will only include one year, the centennial year, that starts with the century's number (e.g. 1900 is the final year in the 19th century).

End of the 20th century

It is commonly-held misconception that the 20th century ended on December 31, 1999. The 20th century actually ended on December 31, 2000, its centennial year.

1st century AD and BC

There is no "zeroth century" in between the first century BC and the first century AD. The first century BC includes the years 100 BC to 1 BC. Other centuries BC follow the same pattern.

Dating Systems before the Century

The oldest dating systems were based on the reigns of monarchs, (e.g. the fifteenth year of King George). Similarly, other systems arose dating from the founding of a dynasty, city or religion. For example, Ab urbe condita counts the Year 1 as the founding of Rome, Anno Domini as the first full year of Jesus Christ's life and the Islamic calendar counts in the year of the Hijra. The Gregorian calendar adopted Anno Domini as the basis for its numbering system.

Centuries in Astronomical Year Numbering

Astronomical year numbering, used by astronomers, includes a year zero (0). Consequently, the first century in these calendars may designate the years 0 to 99 as the first century, years 100 to 199 as the second etc. However, in order to regard 2000 as the first year of the twenty-first century according to the astronomical year numbering, the astronomical year 0 has to correspond to the Gregorian year 1 BC.

References

"The Battle of the Centuries", Ruth Freitag, U.S. Government Printing Office. Available from the Superintendent of Documents, P.O. Box 371954, Pittsburgh, PA 15250- 7954. Cite stock no. 030-001-00153-9.

See also

• List of centuries

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