aikayksiköitä

Aikayksiköitä (Finnish: "time units") are standardized quantities used to measure intervals and moments in time. The base unit in the International System of Units (SI) is the second, defined by the fixed frequency of the cesium‑133 atomic transition (9,192,631,770 periods). Other units are multiples or subdivisions of the second and are used in everyday life, science and engineering.

Common multiples include the minute (60 seconds), hour (3,600 seconds), and day (24 hours, nominally 86,400 seconds). Weeks, months and years are larger civil units; months vary in length while the Gregorian year is typically 365 days with leap years of 366 days. Astronomical and scientific contexts also use units such as the Julian year (exactly 365.25 days) and the sidereal day (about 23h 56m 4.1s). Subsecond units include milliseconds, microseconds, nanoseconds and smaller scales used in computing, electronics and ultrafast physics.

Timekeeping systems and standards—such as Coordinated Universal Time (UTC)—combine atomic time with occasional leap seconds to remain aligned with Earth's rotation. Calendars organize longer units for civil, religious and cultural purposes. ISO 8601 provides widely used conventions for representing dates, times and durations in data interchange. Accurate and consistent time units are essential across navigation, communications, scientific measurement and daily life.