Beginning and ending of centuries
Although a century can refer to any arbitrary 100-year period, there are two schools of thought on what a conventional century is. The first is predicated on exact construction, whereas the second is predicated on general perception.
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The first century of the Christian era covered the years 1 to 100 AD, the second century covered 101 to 200 AD, and so on. This is known as rigid construction. According to this paradigm, the n-th century begins in the year that ends in “01” and ends in the year that ends in “00.” In precise use, the 20th century is made up of the years 1901 through 2000.
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According to common belief and usage, centuries are organized by classifying years into groups based on whether they share the “hundreds” figure (s). According to this paradigm, the n-th century begins in the year that ends in “00” and ends in the year that ends in “99”; for instance, the 20th century in popular culture spans the years 1900 to 1999.
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The astronomical year numbering and ISO 8601 systems both include a year zero, with the astronomical year 0 equating to the year 1 BCE, the astronomical year -1 corresponding to the year 2 BCE, and so on. This makes calendrical computations by computers easier.