Definition:Time/Unit/Year - ProofWiki (original) (raw)

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 mathrmyr\mathrm {yr}mathrmyr or mathrmy\mathrm ymathrmy.

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

Also see

There are others.

Sources