Modern Timekeeping and Calendars

Core concept

Modern clocks now use extremely precise atomic clocks, which measure time based on the vibrations of atoms (typically caesium), accurate to within a fraction of a second over millions of years — far more precise than any mechanical or natural method. Calendars, though based on astronomical cycles, are also shaped by cultural and religious traditions, which is why different calendar systems (like the lunar Islamic calendar or lunisolar Hindu calendar) exist alongside the widely used solar Gregorian calendar.