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The year is a derived unit of time.

\(\ds \) \(\) \(\ds 1\) year
\(\ds \) \(\approx\) \(\ds 365 \cdotp 24219 \, 878\) days
\(\ds \) \(\approx\) \(\ds 365 \cdotp 24219 \, 878 \times 24 \times 60 \times 60\) seconds

That is:

\(\ds \) \(\) \(\ds 1\) year
\(\ds \) \(\approx\) \(\ds 365\) days,
\(\ds \) \(\) \(\ds 5\) hours,
\(\ds \) \(\) \(\ds 48\) minutes, and
\(\ds \) \(\) \(\ds 45 \cdotp 9747\) seconds

It is defined to be equal to the orbital period of Earth round the sun.

Calendar Year

A calendar year is the number of days between dates with the same designation in adjacent years.

As a year is not an integral number of days, it is necessarily an approximation to the actual year.

\(\ds \) \(\) \(\ds 1\) calendar year
\(\ds \) \(=\) \(\ds 12\) months usually, depending on the calendar used
\(\ds \) \(=\) \(\ds 365 \text{ or } 366\) days, usually, but it depends on the calendar used


The symbol for the year is $\mathrm {yr}$ or $\mathrm y$.

In some scientific contexts $\mathrm a$ (for annus, Latin for year) is used.

Also known as

The year as defined here is also known as a tropical year to distinguish it from the various other types of year.

Also see

There are others.