# How does the earth-sun-moon system relate to the way in which we measure time?

Nov 4, 2016

See explanation.

#### Explanation:

Earth's day/night spin-period is called day. This day decides second as the unit of time. A second is defined by

$\text{1 day" = "24 hours" xx "60 min"/"1 hour" xx "60 sec"/"1 min" = "86400 sec}$

The day-night break-up at a location, within this $24$-hour day, is related to latitude and the day of the year. This break up is irrelevant, for fixing second as a unit of time.

The (Earth) year unit is the number of days taken by the center of the Earth to make one complete revolution, about the center of the Sun. This Earth year $=$ $\text{365.256363004 days}$, nearly. This is called a sidereal year.

Importantly, the day/night spin period and the period of revolution of every other solar orbiter are expressed in units of Earth-day and Earth-year,