Definition:Calendar/Gregorian/Year
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Definition
A Gregorian year, also known as the civil year, is the length of a year as defined using the Gregorian calendar.
- $1$ Gregorian year $= \begin{cases} 366 \, \text {days} & : 400 \divides y \\
365 \, \text {days} & : 400 \nmid y \text { and } 100 \divides y \\ 366 \, \text {days} & : 100 \nmid y \text { and } 4 \divides y \\ 365 \, \text {days} & : 4 \nmid y \end{cases}$
where:
- $y$ denotes the number of the year
- $4 \divides y$ denotes that $y$ is divisible by $4$
- $4 \nmid y$ denotes that $y$ is not divisible by $4$.
Also known as
A Gregorian year is also known as the civil year.
Some sources also call it a calendar year, which for many societies it actually is.
However, there are some societies which use a different calendars, and so to them a calendar year is a different construct altogether.
Also see
Sources
- 1986: David Wells: Curious and Interesting Numbers ... (previous) ... (next): $365 \cdotp 2422$
- 1997: David Wells: Curious and Interesting Numbers (2nd ed.) ... (previous) ... (next): $365 \cdotp 24219 \, 878$
- 1998: David Nelson: The Penguin Dictionary of Mathematics (2nd ed.) ... (previous) ... (next): year
- 2008: David Nelson: The Penguin Dictionary of Mathematics (4th ed.) ... (previous) ... (next): year