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A century (from the Latin centum meaning one hundred) is one hundred consecutive years. Centuries are numbered ordinally in English and many other languages (e.g. "the 7th century AD/CE"). Contents 1 Start and end in the Gregorian Calendar 1.1 1st century BC and AD 2 Dating units in other calendar systems 3 Centuries in astronomical year numbering 4 Alternative naming systems 5 Notes and references 6 See also Start and end in the Gregorian Calendar

According to the Gregorian calendar the 1st century AD/CE started on January 1 1 and ended on December 31 100. The 2nd century started at year 101 the 3rd at 201 etc. The n-th century started/will start on the year (100n)-99 and ends in 100n . 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). 1st century BC and AD

There is no "zeroth century" in between the 1st century BC and the 1st century AD. Also there is no year 0 AD.1 The Julian calendar "jumps" from 1 BC to 1 AD. The first century BC includes the years 100 BC to 1 BC. Other centuries BC follow the same pattern. Dating units in other calendar systems

Besides the Gregorian calendar the Julian calendar and the Hindu calendar have cycles of years which are used to delineate whole time periods; the Hindu calendar in particular summarizes its years into groups of 60. Centuries in astronomical year numbering

Astronomical year numbering used by astronomers includes a year zero (0). Consequently the 1st century in these calendars may designate the years 0 to 99 as the 1st century years 100 to 199 as the second etc. However in order to regard 2000 as the first year of the 21st century according to the astronomical year numbering the astronomical year 0 has to correspond to the Gregorian year 1 BC. Alternative naming systems

In Swedish Danish Norwegian and Finnish centuries are typically not named ordinally but according to the hundreds part of the year and consequently centuries start at even multiples of 100. For example Swedish nittonhundratalet (or 1900-talet) Danish and Norwegian nittenhundredetallet (or 1900-tallet) and Finnish tuhatyhdeksnsataaluku (or 1900-luku) refer unambiguously to the years 19001999. The same system is used informally in English. For example the years 19001999 are sometimes referred to as the nineteen hundreds (1900s). This is similar to the English decade names (1980s meaning the years 19801989). Notes and references Two separate systems that also do not use religious titles the astronomical system and the ISO 8601 standard do use a year zero. The year 1 BC (identical to the year 1 BC) is represented as 0 in the astronomical system and as 0000 in ISO 8601. Presently ISO 8601 dating requires usage of the Gregorian calendar for all dates however whereas astronomical dating and Common Era dating allow usage of the Julian calendar for dates before 1582 AD.

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 Look up century in Wiktionary the free dictionary. List of centuries Millennium Lustrum Decade v d eTime measurement and standards Major subjects Time  Chronometry  Orders of magnitude  Metrology International standards UTC  UTC offset  UT  DUT1  IERS  ISO 31-1  ISO 8601  TAI  12-hour clock  24-hour clock  Barycentric Coordinate Time  Civil time  Daylight saving time  Geocentric Coordinate Time  International Date Line  Leap second  Solar time  Terrestrial Time  Time zone Obsolete standards Barycentric Dynamical Time  Ephemeris time  Greenwich Mean Time  Prime Meridian Time in physics Absolute time and space  Spacetime  Chronon  Continuous time  Coordinate time  Cosmological decade  Discrete time  Planck epoch  Planck time  Proper time  Theory of relativity  Time dilation  Gravitational time dilation  Time domain  T-symmetry Horology Clock  Astrarium  Atomic clock  Complication  Equation of time  History of timekeeping devices  Hourglass  Marine chronometer  Marine sandglass  Radio clock  Sundial  Watch  Water clock Calendar Astronomical  Calculating the day of the week  Dominical letter  Epact  Equinox  Gregorian  Intercalation  Islamic  Julian  Leap year  Lunar  Lunisolar  Seven-day week  Solar  Solstice  Tropical year  Week-day names Archaeology & geology Dating methodologies  Geologic time scale  International Commission on Stratigraphy Astronomical chronology Galactic year  Nuclear time scale  Precession  Sidereal time Units of time Century  Day  Decade  Fortnight  Hour  Jiffy  Lustrum  Millennium  Minute  Month  Saeculum  Second  Shake  Tide  Week  Year Related topics Chronology  Duration  Mental chronometry  Metric time  System time  Time value of money  Timekeeper