Definition:Calendar/Gregorian/Year

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

• Discrepancy between Gregorian Year and Tropical Year

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