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- Time_standard abstract "A time standard is a specification for measuring time: either the rate at which time passes; or points in time; or both. In modern times, several time specifications have been officially recognized as standards, where formerly they were matters of custom and practice. An example of a kind of time standard can be a time scale, specifying a method for measuring divisions of time. A standard for civil time can specify both time intervals and time-of-day. Standardized time measurements are made using a clock to count periods of some cyclic change, which may be either the changes of a natural phenomenon or of an artificial machine.Historically, time standards were often based on the Earth's rotational period. From the late 17th century to the 19th century it was assumed that the Earth's daily rotational rate was constant. Astronomical observations of several kinds, including eclipse records, studied in the 19th century, raised suspicions that the rate at which Earth rotates is gradually slowing and also shows small-scale irregularities, and this was confirmed in the early twentieth century. Time standards based on Earth rotation were replaced (or initially supplemented) for astronomical use from 1952 onwards by an ephemeris time standard based on the Earth's orbital period and in practice on the motion of the Moon. The invention in 1955 of the caesium atomic clock has led to the replacement of older and purely astronomical time standards, for most practical purposes, by newer time standards based wholly or partly on atomic time. Various types of second and day are used as the basic time interval for most time scales. Other intervals of time (minutes, hours, and years) are usually defined in terms of these two.".
- Time_standard wikiPageExternalLink leapsec.html.
- Time_standard wikiPageExternalLink systime.html.
- Time_standard wikiPageExternalLink clock_comparisons.html.
- Time_standard wikiPageExternalLink tai.html.
- Time_standard wikiPageExternalLink times.html.
- Time_standard wikiPageExternalLink article.cfm?id=experts-time-division-days-hours-minutes.
- Time_standard wikiPageExternalLink timescales.html.
- Time_standard wikiPageID "41799".
- Time_standard wikiPageRevisionID "594540198".
- Time_standard hasPhotoCollection Time_standard.
- Time_standard subject Category:Time_scales.
- Time_standard type Abstraction100002137.
- Time_standard type Duration115133621.
- Time_standard type FundamentalQuantity113575869.
- Time_standard type Measure100033615.
- Time_standard type TimePeriod115113229.
- Time_standard type TimeScale115134691.
- Time_standard type TimeScales.
- Time_standard comment "A time standard is a specification for measuring time: either the rate at which time passes; or points in time; or both. In modern times, several time specifications have been officially recognized as standards, where formerly they were matters of custom and practice. An example of a kind of time standard can be a time scale, specifying a method for measuring divisions of time. A standard for civil time can specify both time intervals and time-of-day.".
- Time_standard label "Estándar de tiempo".
- Time_standard label "Time standard".
- Time_standard label "Zeitskala".
- Time_standard label "時刻系".
- Time_standard label "時間標準".
- Time_standard sameAs Zeitskala.
- Time_standard sameAs Estándar_de_tiempo.
- Time_standard sameAs 時刻系.
- Time_standard sameAs m.0bh8f.
- Time_standard sameAs Q6313217.
- Time_standard sameAs Q6313217.
- Time_standard sameAs Time_standard.
- Time_standard wasDerivedFrom Time_standard?oldid=594540198.
- Time_standard isPrimaryTopicOf Time_standard.