Metric time

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. Metric time is a measure of time intervals, while decimal time is a means of recording time of day.

History

The second derives its name from the sexagesimal system, which originated with the Sumerians and Babylonians. This system divides a base unit into sixty minutes, each minute into sixty seconds, and each second into sixty tierces.[1] The word "minute" comes from the Latin pars minuta prima, meaning "first small part", and "second" from pars minuta secunda or "second small part". 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.

On March 28, 1794, the president of the French commission that developed the metric system, Joseph Louis Lagrange, proposed using the day (French jour) as the base unit of time, with divisions déci-jour and centi-jour (deciday and centiday in English).[2] The final system, as introduced in 1795, included units for length, area, dry volume, liquid capacity, weight or mass, and currency, but not time. Decimal time of day had been introduced in France two years earlier, but was set aside 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, 1/1000, 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. The centiday, (called in Chinese) was used in China for thousands of years. A centiday is about 14.4 minutes. In the 19th century, Joseph Charles François de Rey-Pailhade proposed using the centiday, abbreviated , divided into 10 decicés, 100 centicés, 1000 millicés.[3] and 10000 dimicés.[4][5]

James Clerk Maxwell and Elihu Thomson (through the British Association for the Advancement of Science - BAAS) introduced the 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.[6]

When the modern SI system was defined at the 10th 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 FILETIME as multiples of 100ns since January 1, 1601.[7] VAX/VMS uses the number of 100ns since November 17, 1858 and RISC OS the number of centiseconds since January 1, 1900.

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
103 kilosecond 1 000 16.7 minutes
106 megasecond 1 000 000 11.6 days
109 gigasecond 1 000 000 000 31.7 years

See also

References

  1. ^ "What does tierce mean". findwords.info. Retrieved 2016-03-23.
  2. ^ Procès-verbaux du Comité d'instruction publique de la Convention nationale by James Guillaume
  3. ^ Histoire d'heure - Fractionnement du temps Archived 2015-05-22 at the Wayback Machine
  4. ^ AJB, Volume 9, 1907
  5. ^ Report of the Sixth International Geographical Congress: Held in London, 1895
  6. ^ Einstein's Clocks, Poincare's Maps: empires of time By Peter Louis Galison
  7. ^ FILETIME documentation on MSDN

External links

24-hour clock

The 24-hour clock is the convention of time keeping in which the day runs from midnight to midnight and is divided into 24 hours, indicated by the hours passed since midnight, from 0 to 23. This system is the most commonly used time notation in the world today, and is used by international standard ISO 8601.A limited number of countries, particularly English-speaking, use the 12-hour clock, or a mixture of the 24- and 12-hour time systems. In countries where the 12-hour clock is still dominant, some professions prefer to use the 24-hour clock. For example, in the practice of medicine the 24-hour clock is generally used in documentation of care as it prevents any ambiguity as to when events occurred in a patient's medical history. In the United States and a handful of other countries, it is popularly referred to as military time.

Bob Brozman

Bob Brozman (March 8, 1954 – April 23, 2013) was an American guitarist and ethnomusicologist.

Calendar reform

Calendar reform or calendrical reform, is any significant revision of a calendar system. The term sometimes is used instead for a proposal to switch to a different calendar design.

Day

A day is approximately the period of time during which the Earth completes one rotation around its axis. A solar day is the length of time which elapses between the Sun reaching its highest point in the sky two consecutive times.In 1960, the second was redefined in terms of the orbital motion of the Earth in year 1900, and was designated the SI base unit of time. The unit of measurement "day", was redefined as 86,400 SI seconds and symbolized d. In 1967, the second and so the day were redefined by atomic electron transition. A civil day is usually 86,400 seconds, plus or minus a possible leap second in Coordinated Universal Time (UTC), and occasionally plus or minus an hour in those locations that change from or to daylight saving time.Day can be defined as each of the twenty-four-hour periods, reckoned from one midnight to the next, into which a week, month, or year is divided, and corresponding to a rotation of the earth on its axis. However its use depends on its context, for example when people say 'day and night', 'day' will have a different meaning. It will mean the interval of light between two successive nights; the time between sunrise and sunset, in this instance 'day' will mean time of light between one night and the next. However, in order to be clear when using 'day' in that sense, "daytime" should be used to distinguish it from "day" referring to a 24-hour period; this is since daytime usually always means 'the time of the day between sunrise and sunset. The word day may also refer to a day of the week or to a calendar date, as in answer to the question, "On which day?" The life patterns (circadian rhythms) of humans and many other species are related to Earth's solar day and the day-night cycle.

Decimal time

Decimal time is the representation of the time of day using units which are decimally related. This term is often used specifically to refer to the time system used in France for a few years beginning in 1792 during the French Revolution, which divided the day into 10 decimal hours, each decimal hour into 100 decimal minutes and each decimal minute into 100 decimal seconds, as opposed to the more familiar UTC time standard, which divides the day into 24 hours, each hour into 60 minutes and each minute into 60 seconds.

The main advantage of a decimal time system is that, since the base used to divide the time is the same as the one used to represent it, the whole time representation can be handled as a single string. Therefore, it becomes simpler to interpret a timestamp and to perform conversions. For instance, 1:23:00 is 1 decimal hour and 23 decimal minutes, or 1.23 hours, or 123 minutes; 3 hours is 300 minutes or 30,000 seconds.

This property also makes it straightforward to represent a timestamp as a fractional day, so that 2019-05-23.534 can be interpreted as five decimal hours and 34 decimal minutes after the start of that day, or 0.534 (53.4%) through that day. It also adjusts well to digital time representation using epochs, in that the internal time representation can be used directly both for computation and for user-facing display.

Exact solutions in general relativity

In general relativity, an exact solution is a Lorentzian manifold equipped with tensor fields modeling states of ordinary matter, such as a fluid, or classical nongravitational fields such as the electromagnetic field.

Future orientation

Future orientation is broadly defined as the extent to which an individual thinks about the future, anticipates future consequences, and plans ahead before acting. Across development, future orientation is particularly important during periods of major changes, for example during the transition from adolescence to adulthood, when youth must make choices about social groups, academic paths, as well as risky behaviors like drug and alcohol use, and sexual activity. Several models have been developed to describe the various factors that combine to impact future orientation.

Hexadecimal time

Hexadecimal time is the representation of the time of day as a hexadecimal number in the interval [0,1).

The day is divided into 1016 (1610) hexadecimal hours, each hour into 10016 (25610) hexadecimal minutes, and each minute into 1016 (1610) hexadecimal seconds.

Hour

An hour (symbol: h; also abbreviated hr.) is a unit of time conventionally reckoned as ​1⁄24 of a day and scientifically reckoned as 3,599–3,601 seconds, depending on conditions.

The hour was initially established in the ancient Near East as a variable measure of ​1⁄12 of the night or daytime. Such seasonal, temporal, or unequal hours varied by season and latitude. The hour was subsequently divided into 60 minutes, each of 60 seconds. Equal or equinoctial hours were taken as ​1⁄24 of the day as measured from noon to noon; the minor seasonal variations of this unit were eventually smoothed by making it ​1⁄24 of the mean solar day. Since this unit was not constant due to long term variations in the Earth's rotation, the hour was finally separated from the Earth's rotation and defined in terms of the atomic or physical second.

In the modern metric system, hours are an accepted unit of time defined as 3,600 atomic seconds. However, on rare occasions an hour may incorporate a positive or negative leap second, making it last 3,599 or 3,601 seconds, in order to keep it within 0.9 seconds of UT1, which is based on measurements of the mean solar day.

Hourglass

An hourglass (or sandglass, sand timer, sand clock or egg timer) is a device used to measure the passage of time. It comprises two glass bulbs connected vertically by a narrow neck that allows a regulated trickle of material (historically sand) from the upper bulb to the lower one. Factors affecting the time it measured include sand quantity, sand coarseness, bulb size, and neck width. Hourglasses may be reused indefinitely by inverting the bulbs once the upper bulb is empty. Depictions of hourglasses in art survive in large numbers from antiquity to the present day, as a symbol for the passage of time. These were especially common sculpted as epitaphs on tombstones or other monuments, also in the form of the winged hourglass, a literal depiction of the well-known Latin epitaph tempus fugit ("time flies").

Il Tempo (horse)

Il Tempo was a champion New Zealand thoroughbred racehorse, by Time and Again out of Timing. He is probably New Zealand's greatest ever stayer, having won the Auckland Cup two times, and also the Wellington Cup once. The Wellington Cup was over 2 miles and he won it in a World Record time of 3:16.2, a record which still stands today.

Il Tempo also won the Chalmers Handicap over two miles, plus being placed over the two mile distance several times. He was trained by Mr Bruce Priscott, a butcher by trade. Normally he was ridden by jockey Noel D Riordan.

He had a fantastic fresh up record. Il Tempo also won a weight for age over one and a half miles. Normally a powerful finishing back runner, in a very small field he eventually took up the running and then was passed by the whole field and then came again to mow them down.

Il Tempo was top-weight and hot pre-post favorite for the 1970 Melbourne Cup, but did not race. In his preparation for the cup, he broke down after running a 1 min. 39.0 sec. mile in a training gallop. He never raced again.

List of unusual units of measurement

An unusual unit of measurement is a unit of measurement that does not form part of a coherent system of measurement; especially in that its exact quantity may not be well known or that it may be an inconvenient multiple or fraction of base units in such systems.

This definition is not exact since it includes units such as the week or the light-year are quite "usual" in the sense that they are often used but which can be "unusual" if taken out of their common context, as demonstrated by the Furlong/Firkin/Fortnight (FFF) system of units.

Many of the unusual units of measurements listed here are colloquial measurements, units devised to compare a measurement to common and familiar objects.

Miles per hour

Miles per hour (abbreviated mph, MPH or mi/h) is an imperial and United States customary unit of speed expressing the number of statute miles covered in one hour. It is used in the United States, United Kingdom and some Commonwealth nations, notably in the Caribbean region.

Philosophy of physics

In philosophy, philosophy of physics deals with conceptual and interpretational issues in modern physics, and often overlaps with research done by certain kinds of theoretical physicists. Philosophy of physics can be very broadly lumped into three main areas:

The interpretations of quantum mechanics: Concerning issues, mainly, with how to formulate an adequate response to the measurement problem, and understand what the theory tells us about reality.

The nature of space and time: Are space and time substances, or purely relational? Is simultaneity conventional or just relative? Is temporal asymmetry purely reducible to thermodynamic asymmetry?

Inter-theoretic relations: the relationship between various physical theories, such as thermodynamics and statistical mechanics. This overlaps with the issue of scientific reduction.

Rindler coordinates

In relativistic physics, the coordinates of a hyperbolically accelerated reference frame constitute an important and useful coordinate chart representing part of flat Minkowski spacetime. In special relativity, a uniformly accelerating particle undergoes hyperbolic motion, for which a uniformly accelerating frame of reference in which it is at rest can be chosen as its proper reference frame. The phenomena in this hyperbolically accelerated frame can be compared to effects arising in a homogeneous gravitational field. For general overview of accelerations in flat spacetime, see Acceleration (special relativity) and Proper reference frame (flat spacetime).

In this article, the speed of light is defined by c = 1, the inertial coordinates are (X,Y,Z,T), and the hyperbolic coordinates are (x,y,z,t). These hyperbolic coordinates can be separated into two main variants depending on the accelerated observer's position: If the observer is located at time T = 0 at position X = 1/α (with α as the constant proper acceleration measured by a comoving accelerometer), then the hyperbolic coordinates are often called Rindler coordinates with the corresponding Rindler metric. If the observer is located at time T = 0 at position X = 0, then the hyperbolic coordinates are sometimes called Møller coordinates or Kottler-Møller coordinates with the corresponding Kottler-Møller metric. An alternative chart often related to observers in hyperbolic motion is obtained using Radar coordinates which are sometimes called Lass coordinates. Both the Kottler-Møller coordinates as well as Lass coordinates are denoted as Rindler coordinates as well.Regarding the history, such coordinates were introduced soon after the advent of special relativity, when they were studied (fully or partially) alongside the concept of hyperbolic motion: In relation to flat Minkowski spacetime by Albert Einstein (1907, 1912), Max Born (1909), Arnold Sommerfeld (1910), Max von Laue (1911), Hendrik Lorentz (1913), Friedrich Kottler (1914), Wolfgang Pauli (1921), Karl Bollert (1922), Stjepan Mohorovičić (1922), Georges Lemaître (1924), Einstein & Nathan Rosen (1935), Christian Møller (1943, 1952), Fritz Rohrlich (1963), Harry Lass (1963), and in relation to both flat and curved spacetime of general relativity by Wolfgang Rindler (1960, 1966). For details and sources, see section on history.

Swatch Internet Time

Swatch Internet Time (or .beat time) is a decimal time concept introduced in 1998 by the Swatch corporation as part of their marketing campaign for their line of "Beat" watches.

Instead of hours and minutes, the mean solar day is divided into 1000 parts called ".beats". Each .beat is equal to one decimal minute in the French Revolutionary decimal time system and lasts 1 minute and 26.4 seconds (86.4 seconds) in standard time. Times are notated as a 3-digit number out of 1000 after midnight. So, @248 would indicate a time 248 .beats after midnight representing 248/1000 of a day, just over 5 hours and 57 minutes.

There are no time zones in Swatch Internet Time; instead, the new time scale of Biel Meantime (BMT) is used, based on Swatch's headquarters in Biel, Switzerland and equivalent to Central European Time, West Africa Time, and UTC+01. Unlike civil time in Switzerland and many other countries, Swatch Internet Time does not observe daylight saving time.

Term (time)

A term is a period of duration, time or occurrence, in relation to an event. To differentiate an interval or duration, common phrases are used to distinguish the observance of length are near-term or short-term, medium-term or mid-term and long-term.

It is also used as part of a calendar year, especially one of the three parts of an academic term and working year in the United Kingdom: Michaelmas term, Hilary term / Lent term or Trinity term / Easter term, the equivalent to the American semester. In America there is a midterm election held in the middle of the four-year presidential term, there are also academic midterm exams.

In economics, it is the period required for economic agents to reallocate resources, and generally reestablish equilibrium. The actual length of this period, usually numbered in years or decades, varies widely depending on circumstantial context. During the long term, all factors are variable.

In finance or financial operations of borrowing and investing, what is considered long-term is usually above 3 years, with medium-term usually between 1 and 3 years and short-term usually under 1 year. It is also used in some countries to indicate a fixed term investment such as a term deposit.

In law, the term of a contract is the duration for which it is to remain in effect (not to be confused with the meaning of "term" that denotes any provision of a contract). A fixed-term contract is one concluded for a pre-defined time, although it may also include provision for it to be extended. A contractor required to deliver against a term contract is often referred to as a "term contractor".

Time signature

The time signature (also known as meter signature, metre signature, or measure signature) is a notational convention used in Western musical notation to specify how many beats (pulses) are contained in each measure (bar), and which note value is equivalent to a beat.

In a music score, the time signature appears at the beginning as a time symbol or stacked numerals, such as or 34 (read common time and three-four time, respectively), immediately following the key signature (or immediately following the clef symbol if the key signature is empty). A mid-score time signature, usually immediately following a barline, indicates a change of meter.

There are various types of time signatures, depending on whether the music follows regular (or symmetrical) beat patterns, including simple (e.g., 34 and 44), and compound (e.g., 98 and 128); or involves shifting beat patterns, including complex (e.g., 54 or 78), mixed (e.g., 58 & 38 or 68 & 34), additive (e.g., 3+2+38), fractional (e.g., ​2 1⁄24), and irrational meters (e.g., 310 or 524).

Time zone

A time zone is a region of the globe that observes a uniform standard time for legal, commercial, and social purposes. Time zones tend to follow the boundaries of countries and their subdivisions because it is convenient for areas in close commercial or other communication to keep the same time.

Most of the time zones on land are offset from Coordinated Universal Time (UTC) by a whole number of hours (UTC−12:00 to UTC+14:00), but a few zones are offset by 30 or 45 minutes (e.g. Newfoundland Standard Time is UTC−03:30, Nepal Standard Time is UTC+05:45, and Indian Standard Time is UTC+05:30).

Some higher latitude and temperate zone countries use daylight saving time for part of the year, typically by adjusting local clock time by an hour. Many land time zones are skewed toward the west of the corresponding nautical time zones. This also creates a permanent daylight saving time effect.

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