The week equals 7 days โ an invention of the ancient Babylonians linked to the 7 classical planetary bodies visible to the naked eye. The 7-day week is nearly universal today, used by all major calendar systems.
Real-world: UK workweek: MonโFri. US payroll cycle often biweekly. Pregnancy duration: 40 weeks.
Read full week reference โThe day equals 86,400 seconds โ the mean time for Earth to complete one rotation relative to the Sun (solar day). A sidereal day (relative to distant stars) is about 4 minutes shorter: 23 h 56 min 4 s. Most practical usage means solar day.
Real-world: International shipping: 2โ7 days typical. Global work-week: 5 days in most countries. Human circadian rhythm: 24 h ยฑ 30 min.
Read full day reference โ