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A unit of time is any particular time interval, used as a standard way of measuring or expressing duration. The base unit of time in the International System of Units (SI), and by extension most of the Western world , is the second , defined as about 9 billion oscillations of the caesium atom.
An order of magnitude of time is usually a decimal prefix or decimal order-of-magnitude quantity together with a base unit of time, like a microsecond or a million years. In some cases, the order of magnitude may be implied (usually 1), like a "second" or "year". In other cases, the quantity name implies the base unit, like "century". In most ...
This category identifies units of time, either general (in Chronology) or for specific scientific and other uses; and some closely related notions.
Metric time is the measure of time intervals using the metric system. The modern SI system defines the second as the base unit of time, and forms multiples and submultiples with metric prefixes such as kiloseconds and milliseconds. Other units of time – minute, hour, and day – are accepted for use with SI, but are not part of it
In the International System of Units (SI), the unit of time is the second (symbol: s). It has been defined since 1967 as "the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom", and is an SI base unit. [12]
One unit derived from the FFF system of units is the microfortnight, one millionth of the fundamental time unit of FFF, which equals 1.2096 seconds. This is a fairly representative example of " hacker humor ", [ 66 ] and is occasionally used in operating systems; for example, the OpenVMS TIMEPROMPTWAIT parameter is measured in microfortnights.
The unit is used to measure the length of the Harvard Bridge. Canonically, and originally, in 1958 when Smoot was a Lambda Chi Alpha pledge at MIT (class of 1962), the bridge was measured to be 364.4 Smoots, plus or minus one ear, using Mr. Smoot himself as a ruler. [17] At the time, Smoot was 5 feet, 7 inches, or 170 cm, tall. [18]
Some common examples of such units are the customary units of time, namely the minute (conversion factor of 60 s/min, since 1 min = 60 s), the hour (3600 s), and the day (86 400 s); the degree (for measuring plane angles, 1° = π ⁄ 180 rad); and the electronvolt (a unit of energy, 1 eV = 1.602 176 634 × 10 −19 J). [2]