Definition:Time/Unit/Year

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Definition

The year is a derived unit of time.

It is based on the orbital period of Earth round the sun.


Tropical Year

The tropical year is the time interval between two consecutive passages, in the same direction, of the Sun through the equatorial plane of Earth.


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


That is:

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


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


Symbol

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 see

There are others.

  • Results about year can be found here.


Sources

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