Metric time

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Not to be confused with Decimal time.
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Metric time is the measure of time intervals using the

time of day
.

History

The second derives its name from the

Angular measure also uses sexagesimal units; there, it is the degree
that is subdivided into minutes and seconds, while in time, it is the hour.

In 1790, French diplomat

Paris Meridian between the equator and the North Pole.[1][2][3][4][5]

The commission initially proposed the decimal time units later enacted as part of the new

Decimal time of day
had been introduced in France two years earlier, but mandatory use was suspended at the same time the metric system was inaugurated, and did not follow the metric pattern of a base unit and prefixed units.

Base units equivalent to decimal divisions of the day, such as 1/10, 1/100, 1/1,000, or 1/100,000 day, or other divisions of the day, such as 1/20 or 1/40 day, have also been proposed, with various names. Such alternative units did not gain any notable acceptance. In China, during the

Song Dynasty, a day was divided into smaller units, called kè (刻). One kè was usually defined as 1⁄100 of a day until 1628, though there were short periods before then where days had 96, 108 or 120 kè.[7] A kè is about 14.4 minutes, or 14 minutes 24 seconds. In the 19th century, Joseph Charles François de Rey-Pailhade endorsed Lagrange’s proposal of using centijours, but abbreviated cé, and divided into 10 decicés, 100 centicés, 1,000 millicés,[8] and 10,000 dimicés.[9][10]

Centimetre gram second system of units in 1874 to derive electric and magnetic metric units, following the recommendation of Carl Friedrich Gauss
in 1832.

In 1897, the Commission de décimalisation du temps was created by the French

Bureau of Longitude, with the mathematician Henri Poincaré as secretary. The commission proposed making the standard hour the base unit of metric time, but the proposal did not gain acceptance and was eventually abandoned.[11]

When the modern

General Conference on Weights and Measures (CGPM) in 1954, the ephemeris second (1/86400 of a mean solar day) was made one of the system's base units. Because the Earth's rotation is slowly decelerating at an irregular rate and was thus unsuitable as a reference point for precise measurements, the SI second was later redefined more precisely 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. The international standard atomic clocks
use caesium-133 measurements as their main benchmark.

In computing

In computing, at least internally, metric time gained widespread use for ease of computation. Unix time gives date and time as the number of seconds since January 1, 1970, and Microsoft's NTFS FILETIME as multiples of 100 ns since January 1, 1601. VAX/VMS uses the number of 100 ns since November 17, 1858, and RISC OS the number of centiseconds since January 1, 1900. Microsoft Excel uses number of days (with decimals, floating point) since January 1, 1900.

All these systems present time for the user using traditional units. None of these systems is strictly linear, as they each have discontinuities at leap seconds.

Prefixes

Metric prefixes for subdivisions of a second are commonly used in science and technology. Milliseconds and microseconds are particularly common. Prefixes for multiples of a second are rarely used:

Multiple Name of unit Seconds In common units
101 decasecond 10 0.17 minutes
102 hectosecond 100 1.67 minutes (or 1 minute 40 seconds)
103 kilosecond 1000 16.7 minutes (or 16 minutes and 40 seconds)
106 megasecond 1000000 11.6 days (or 11 days, 13 hours, 46 minutes and 40 seconds)
109 gigasecond 1000000000 31.7 years (or 31 years, 252 days, 1 hour, 46 minutes, 40 seconds, assuming that there are 7 leap years in the interval)

See also

References

  1. ISBN 978-0-7432-1675-3
    .
  2. ^ Schwartz, Randy K. (September 2008). "The Birth of the Meter" (PDF). The Mathematical Association of America. Retrieved 4 April 2023.
  3. ^ Commission des poids et mesures (1793). Haüy, René-Just (ed.). Instruction abrégée sur les mesures déduites de la grandeur de la Terre, uniformes pour toute la République, et sur les calculs relatifs à leur division décimale; par la Commission temporaire des poids & mesures républicaines, en exécution des décrets de la Convention nationale. Édition originale (in French). France: de l'imprimerie nationale exécutive du Louvre (A Paris).
  4. ^ Frangsmyr, Tore; Heilbron, J. L.; Rider, Robin E. (1990). The Quantifying Spirit in the 18th Century. Berkeley: University of California Press.
  5. OL 25945285M
    .
  6. ^ Procès-verbaux du Comité d'instruction publique de la Convention nationale. 1897. p. 605.
  7. ISSN 0004-6264
    .
  8. ^ Histoire d'heure - Fractionnement du temps Archived 2015-05-22 at the Wayback Machine
  9. ^ "AJB, Volume 9, 1907". 1908.
  10. ^ "Report of the Sixth International Geographical Congress: Held in London, 1895". 1896.
  11. ^ "Einstein's Clocks, Poincare's Maps: empires of time By Peter Louis Galison".

External links

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