How does the earth-sun-moon system relate to the way in which we measure time?
Earth's day/night spin-period is called day. This day decides second as the unit of time. A second is defined by
The day-night break-up at a location, within this
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
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,