Editing Century (section)

== Start and end of centuries ==
Although a century can mean any arbitrary period of 100 [[years]], there are two viewpoints on the nature of standard centuries. One is based on strict construction, while the other is based on popular perception.  

According to the strict construction, the 1st century [[AD]], which began with [[AD 1]], ended with [[AD 100]], and the 2nd century with AD [[200]];{{NoteTag|[[AD]] and [[Common Era|CE]] year numbering, which are numerically equivalent, are now commonly used to number years, including those which occurred before these notations were invented; AD did not become widespread in Europe until early in the 2nd millennium.}} in this model, the ''n''-th century starts with a year that follows a year with a multiple of 100 (except the first century as it began after the year [[1 BC]]) and ends with the next coming year with a multiple of 100 (''100n''), i.e. the 20th century comprises the years '''1901''' to '''2000''', and the 21st century comprises the years '''2001''' to '''2100''' in strict usage.<ref>{{cite web |title=When Did the 21st Century Start? |url=https://www.timeanddate.com/counters/mil2000.html#:~:text=The%2021st%20Century%20Started%20in%202001&text=The%20year%20number%20in%20the,BC%2C%3A%20What's%20the%20difference%3F |website=timeanddate.com |access-date=23 November 2020}}</ref>

In common perception and practice, centuries are structured by grouping years based on sharing the 'hundreds' digit(s). In this model, the ''n''-th century starts with the year that ends in "00" and ends with the year ending in "99";<ref>{{Cite web| title = century | work = Oxford Dictionaries| access-date = 20 January 2021| url = https://www.lexico.com/definition/century| archive-url = https://web.archive.org/web/20191230065254/https://www.lexico.com/definition/century| url-status = dead| archive-date = December 30, 2019}}</ref> for example, in [[popular culture]], the years '''1900''' to '''1999''' constitute the 20th century, and the years '''2000''' to '''2099''' constitute the 21st century.<ref>{{Cite web| title = Centuries and How to Refer to Them | work = Merriam-Webster| access-date = 27 April 2021 | url = https://www.merriam-webster.com/words-at-play/centuries-and-how-to-refer-to-them}}</ref> (This is similar to the grouping of [[Decade#0-to-9 decade|"0-to-9 decades"]] which share the 'tens' digit.) 

To facilitate calendrical calculations by computer, the [[astronomical year numbering]] and [[ISO 8601]] systems both contain a [[year zero]], with the astronomical year 0 corresponding to the year 1 BC, the astronomical year -1 corresponding to 2 BC, and so on.<ref>{{Cite web| title = Calendars | work = L.E. Doggett| access-date = 27 April 2021| url = http://charon.nmsu.edu/~lhuber/leaphist.html | archive-url = https://web.archive.org/web/20120210184836/http://charon.nmsu.edu/~lhuber/leaphist.html | url-status = dead | archive-date = 10 February 2012 }}</ref><ref>{{Cite web| title = Year Dating Conventions | work = National Aeronautics and Space Administration| access-date = 27 April 2021| url = https://eclipse.gsfc.nasa.gov/SEhelp/dates.html}}</ref>

{| class="wikitable" style="text-align:center;margin-left:auto; margin-right:auto; border:none;"
|+ Strict vs Popular usage
|-
! style="text-align:left;" | Year
! [[2 BC]]
! [[1 BC]]
! [[AD 1|1]]
! [[AD 2|2]]
! ...
! [[AD 99|99]]
! [[AD 100|100]]
! [[AD 101|101]]
! [[AD 102|102]]
! ...
! [[AD 199|199]]
! [[AD 200|200]]
! [[AD 201|201]]
! [[AD 202|202]]
! ...
! [[AD 1899|1899]]
! [[AD 1900|1900]]
! [[AD 1901|1901]]
! [[AD 1902|1902]]
! ...
! [[AD 1999|1999]]
! [[AD 2000|2000]]
! [[AD 2001|2001]]
! [[AD 2002|2002]]
! ...
![[AD 2025|2025]]
! ...
! 2099
! 2100
! 2101
! 2102
! ...
|-
! style="text-align:left;" | Strict
| colspan="2" style="background-color:#CEF2E0;" | [[1st century BC]]
| colspan="5" style="background-color:#CEF2E0;" | [[1st century]]
| colspan="5" style="background-color:#CEE0F2;" | [[2nd century]]
| colspan="2" style="background-color:#E0CEF2;" | [[3rd century]]
| ...
| colspan="2" style="background-color:#F2CEE0;" | [[19th century]]
| colspan="5" style="background-color:#F2E0CE;" | [[20th century]]
| colspan="7" style="background-color:#CEF2E0;" | [[21st century]]
| colspan="2" style="background-color:#CEE0F2;" | 22nd century
| ...
|-
! style="text-align:left;" | Popular
| colspan="2" style="background-color:#CEF2E0;" | [[1st century BC]]
| colspan="4" style="background-color:#CEF2E0;" | [[1st century]]
| colspan="5" style="background-color:#CEE0F2;" | [[2nd century]]
| colspan="3" style="background-color:#E0CEF2;" | [[3rd century]]
| ...
| colspan="1" style="background-color:#F2CEE0;" | [[19th century]]
| colspan="5" style="background-color:#F2E0CE;" | [[20th century]]
| colspan="7" style="background-color:#CEF2E0;" | [[21st century]]
| colspan="3" style="background-color:#CEE0F2;" | 22nd century
| ...
|}