History/origin: Unlike many units that have had numerous definitions throughout history, the second has only had four different definitions.
It is defined based on cesium frequency, Δ νC, 'by taking the unperturbed ground-state hyperfine transition frequency of the caesium-133 atom to be 9,192,632,770 when expressed in hertz, which is equal to s -1.' This definition was adopted in late 2018, and is largely the same as the previous definition, except that the conditions are more rigorously defined. Secondĭefinition: A second is the base unit of time in the International System of Units (SI). History/origin: The term 'minute' is derived from the Latin 'pars minuta prima' which means the 'first small part.' The minute was originally defined as 1/60 of an hour (60 seconds), based on the average period of Earth's rotation relative to the sun, known as a mean solar day.Ĭurrent use: The minute, as a multiple of the second, is used for all manner of measurements of duration, from timing races, measuring cooking or baking times, number of heart beats per minute, to any number of other applications. Under Coordinated Universal Time, a minute can have a leap second, making the minute equal to 61 rather than 60 seconds. Definition: A minute (symbol: min) is a unit of time based on the second, the base unit of the International System of Units (SI).
