The second (SI The International System of Units is the modern form of the metric system and is generally a system of units of measurement devised around seven base units and the convenience of the number ten. It is the world's most widely used system of measurement, both in everyday commerce and in science symbol: s), sometimes abbreviated sec., is the name of a unit A unit of measurement is a definite magnitude of a physical quantity, defined and adopted by convention and/or by law, that is used as a standard for measurement of the same physical quantity. Any other value of the physical quantity can be expressed as a simple multiple of the unit of measurement of time Time has been defined as the continuum in which events occur in succession from the past to the present and on to the future. Time has also been defined as a one-dimensional quantity used to sequence events, to quantify the durations of events and the intervals between them, and to quantify and measure the motions of objects and other changes, and is the International System of Units The International System of Units is the modern form of the metric system and is generally a system of units of measurement devised around seven base units and the convenience of the number ten. It is the world's most widely used system of measurement, both in everyday commerce and in science (SI) base unit The International System of Units defines seven units of measure as a basic set from which all other SI units are derived. These SI base units and their physical quantities are: of time.^[1] It may be measured using a clock A clock is an instrument used to indicate, keep, and co-ordinate time. The word clock is derived ultimately from the Celtic words clagan and clocca meaning "bell". For horologists and other specialists the term clock continues to mean exclusively a device with a striking mechanism for announcing intervals of time acoustically, by ringing.

Early definitions of the second were based on the apparent motion of the sun around the earth. The solar day Solar time is time kept or measured by the sun; and its basic division, the day, has been recognized and used since the dawn of history. The immediately visible sign of the passage of time by the sun, and the basis of its measurement, is the sun's apparent motion along the daily course that it appears to trace out in the sky from east to west was divided into 24 hours, each of which contained 60 minutes of 60 seconds each, so the second was ¹⁄_86 400 of the mean solar day. However, nineteenth- and twentieth-century astronomical observations revealed that this average time is lengthening, and thus the motion of the earth is no longer considered a suitable standard for definition. With the advent of atomic clocks An atomic clock is a type of clock that uses an atomic resonance frequency standard as its timekeeping element. They are the most accurate time and frequency standards known, and are used as primary standards for international time distribution services, to control the frequency of television broadcasts, and in global navigation satellite systems, it became feasible to define the second based on fundamental properties of nature. Since 1967, the second has been defined to be

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.^[1]

SI prefixes The International System of Units specifies a set of unit prefixes known as SI prefixes or metric prefixes. An SI prefix is a name that precedes a basic unit of measure to indicate a decimal multiple or fraction of the unit. Each prefix has a unique symbol that is prepended to the unit symbol. The SI prefixes are standardized by the International are frequently combined with the word second to denote subdivisions of the second, e.g., the millisecond A millisecond is a thousandth (1/1000) of a second (one thousandth of a second), the microsecond microsecond is an SI unit of time equal to one millionth of a second. Its symbol is µs (one millionth of a second), and the nanosecond A nanosecond is equal to 1000 picoseconds or 1/1000 microsecond. Because the next SI unit is 1000 times larger, times of 10-8 and 10-7 seconds are typically expressed as tens or hundreds of nanoseconds (one billionth of a second). Though SI prefixes may also be used to form multiples of the second such as kilosecond 10−44 s | ... | 10−24 s ... 10−19 s | 10−18 s ... 10−16 s | 10−15 s ... 10−13 s | 1 E-12 ... 1 E-10 s | 10−9 s | 10−8 s | 10−7 s | 10−6 s | 10−5 s | 10−4 s | 10−3 s | 10−2 s | 10−1 s (one thousand seconds), such units are rarely used in practice. The more common larger non-SI units of time are not formed by powers of ten; instead, the second is multiplied by 60 to form a minute The minute is a unit of time equal to 1/60th of an hour or 60 seconds. In the UTC time scale, a minute occasionally has 59 or 61 seconds; see leap second. The minute is not an SI unit; however, it is accepted for use with SI units, which is multiplied by 60 to form an hour The hour is a unit of time. It is not an SI unit but is accepted for use with the SI with the symbol h, which is multiplied by 24 to form a day A day is a unit of time equivalent to approximately 24 hours. It is not an SI unit but it is accepted for use with SI. The SI unit of time is the second.

The second is also the base unit of time in the centimetre-gram-second The centimetre-gram-second system is a metric system of physical units based on centimetre as the unit of length, gram as a unit of mass, and second as a unit of time. All CGS mechanical units are unambiguously derived from these three base units, but there are several different ways of extending the CGS system to cover electromagnetism, metre-kilogram-second A physical system of units that expresses any given measurement using fundamental units of the metre, kilogram, and/or second, metre-tonne-second The metre-tonne-second or mts system of units is a system of physical units. It was invented in France, hence the unit names sthène and pièze, and was adopted only by the Soviet Union in 1933, and abolished there in 1955. It was built on the same principles as the cgs system, but with larger units for industrial use. The cgs system on the other, and foot-pound-second Imperial units or the imperial system is a system of units, first defined in the British Weights and Measures Act of 1824, later refined and reduced. The system came into official use across the British Empire. By the late 20th century most nations of the former empire had officially adopted the metric system as their main system of measurement systems of units.

International second

Under the International System of Units, the second is currently defined as

The second is 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.^[1]

This definition refers to a caesium Caesium or cesium is the chemical element with the symbol Cs and atomic number 55. It is a soft, silvery-gold alkali metal with a melting point of 28 °C (83 °F), which makes it one of only five metals that are liquid at or near room temperature.[note 1] Caesium has physical and chemical properties similar to those of rubidium and potassium. The atom at rest at a temperature of 0 K The kelvin is a unit increment of temperature and is one of the seven SI base units. The Kelvin scale is a thermodynamic (absolute) temperature scale referenced to absolute zero, the absence of all thermal energy. So by definition, the temperature of a substance at absolute zero is zero kelvin (0 K). The secondary reference point on the Kelvin (absolute zero Absolute zero is the theoretical temperature at which entropy would reach its minimum value. The laws of thermodynamics state that absolute zero cannot be reached because this would require a thermodynamic system to be fully removed from the rest of the universe. A system at absolute zero would still possess quantum mechanical zero-point energy), and with appropriate corrections for gravitational time dilation Gravitational time dilation is the effect of time passing at different rates in regions of different gravitational potential; the lower the gravitational potential , the more slowly clocks run. Albert Einstein originally predicted this effect in his theory of relativity and it has since been confirmed by tests of general relativity. The ground state is defined at zero electric In physics, an electric field is a property that describes the space that surrounds electrically charged particles or that which is in the presence of a time-varying magnetic field. This electric field exerts a force on other electrically charged objects. The concept of an electric field was introduced by Michael Faraday and magnetic fields Magnetic fields surround magnetic materials and electric currents and are detected by the force they exert on other magnetic materials and moving electric charges. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field. The second thus defined is consistent with the ephemeris second, which was based on astronomical measurements. (See History below.)

The realization of the standard second is described briefly in a special publication from the National Institute of Science and Technology The National Institute of Science and Technology is an engineering college in Palur Hills, Orissa, India. It was started in 1996 by a few NRIs, some of who belonged to Orissa. This institute was set up and is managed by the SM Charitable Educational Trust with the aim of promoting higher technical education. This was the first engineering college,^[2] and in detail by the National Research Council of Canada The NRC was established in 1916 under the pressure of World War I to advise the government on matters of science and industrial research. In 1932, laboratories were built on Sussex Drive in Ottawa.^[3]

Equivalence to other units of time

1 international second is equal to:

• 1/60 minute The minute is a unit of time equal to 1/60th of an hour or 60 seconds. In the UTC time scale, a minute occasionally has 59 or 61 seconds; see leap second. The minute is not an SI unit; however, it is accepted for use with SI units (but see also leap second A leap second is a positive or negative one-second adjustment to the Coordinated Universal Time time scale that keeps it close to mean solar time. UTC, which is used as the basis for official time-of-day radio broadcasts for civil time, is maintained using extremely precise atomic clocks. To keep the UTC time scale close to mean solar time, UTC is)
• 1/3,600 hour The hour is a unit of time. It is not an SI unit but is accepted for use with the SI with the symbol h
• 1/86,400 day A day is a unit of time equivalent to approximately 24 hours. It is not an SI unit but it is accepted for use with SI. The SI unit of time is the second (IAU The International Astronomical Union is a collection of professional astronomers, at the Ph.D. level and beyond, active in professional research and education in astronomy. Headquartered in Paris, France, it acts as the internationally recognized authority for assigning designations to celestial bodies (stars, planets, asteroids, etc.) and any system of units)
• 1/31,557,600 Julian year In astronomy, a Julian year is a unit of measurement of time defined as exactly 365.25 days of 86,400 SI seconds each, totalling 31,557,600 seconds. The Julian year is the average length of the year in the Julian calendar used in Western societies in previous centuries, and for which the unit is named. Nevertheless, because a Julian year measures (IAU system of units)

History

Before mechanical clocks

The Egyptians subdivided daytime and nighttime into twelve hours each since at least 2000 BC, hence the seasonal variation of their hours. The Hellenistic Hellenistic civilization represents the zenith of Greek influence in the ancient world from 323 BC to about 146 BC ; note, however that Koine Greek language and Hellenistic philosophy and religion are also indisputably elements of the Roman era until Late Antiquity. It was immediately preceded by the Classical Greece period, and immediately astronomers Hipparchus Hipparchus or Hipparch was a Greek astronomer, geographer, and mathematician of the Hellenistic period. He was the founder of Trigonometry (c. 150 BC) and Ptolemy Claudius Ptolemaeus , known in English as Ptolemy (pronounced /ˈtɒləmɪ/), was a Roman citizen of Egypt who wrote in Greek. He was a mathematician, astronomer, geographer, astrologer and a poet of a single epigram in the Greek Anthology. He lived in Egypt under Roman rule, and is believed to have been born in the town of Ptolemais Hermiou in (c. AD 150) subdivided the day sexagesimally Sexagesimal is a numeral system with sixty as its base. It originated with the ancient Sumerians in the 3rd millennium BC, it was passed down to the ancient Babylonians, and it is still used — in a modified form — for measuring time, angles, and the geographic coordinates that are angles and also used a mean hour (¹⁄₂₄ day), but did not use distinctly named smaller units of time. Instead they used simple fractions of an hour.^{[citation needed]}

The day was subdivided sexagesimally, that is by ¹⁄₆₀, by ¹⁄₆₀ of that, by ¹⁄₆₀ of that, etc., to at least six places after the sexagesimal point (a precision of less than 2 microseconds) by the Babylonians Babylonia was an ancient cultural region in central-southern Mesopotamia , with Babylon as its capital. Babylonia emerged when Hammurabi (fl. ca. 1696 – 1654 BC, short chronology) created an empire out of the territories of the former Akkadian Empire. Babylonia adopted the written Semitic Akkadian language for official use, and retained the after 300 BC, but they did not sexagesimally subdivide smaller units of time. For example, six fractional sexagesimal places of a day was used in their specification of the length of the year, although they were unable to measure such a small fraction of a day in real time. As another example, they specified that the mean synodic month was 29;31,50,8,20 days (four fractional sexagesimal positions), which was repeated by Hipparchus and Ptolemy sexagesimally, and is currently the mean synodic month of the Hebrew calendar The Hebrew calendar or Jewish calendar is a lunisolar calendar used by Jews. Today, the calendar is used predominantly for Jewish religious observances. It is used to determine the dates for Jewish holidays, and also to determine appropriate public reading of Torah portions, yahrzeits (dates to commemorate the death of a relative), and daily Psalm, though restated as 29 days 12 hours 793 halakim The helek is a unit of time used in the calculation of the Hebrew calendar. The hour is divided into 1080 halakim. A helek is 31/3 seconds or 1/18 minute. The helek derives from a small Babylonian time period called a she, meaning '"barleycorn", itself equal to 1/72 of a Babylonian time degree (1° of celestial rotation) (where 1 hour = 1080 halakim).^[4] The Babylonians did not use the hour, but did use a double-hour lasting 120 modern minutes, a time-degree lasting four modern minutes, and a barleycorn lasting 3¹⁄₃ modern seconds (the helek of the modern Hebrew calendar).^[5]

In 1000, the Persian The Persian people are defined by the use of the Persian language as their mother tongue. However, the term Persian has also a supra-ethnic significance and has been historically referred to a part of Iranian peoples. The origin of the Persian people is traced to the ancient Indo-Iranians , who arrived in parts of Greater Iran circa 2000-1500 BCE scholar al-Biruni Abū Rayḥān Muḥammad ibn Aḥmad Bīrūnī , often known as Alberonius in Latin, but also Al Beruni, Al Bayrooni or variants, (born 5 September 973 in Kath, Khwarezm (now in Uzbekistan, historically a part of greater Iran), died 13 December 1048 in Ghazni, [Afghanistan) was a Persian Muslim scholar and polymath of the 11th century gave the times of the new moons of specific weeks as a number of days, hours, minutes, seconds, thirds, and fourths after noon Sunday.^[6] In 1267, the medieval scientist Roger Bacon Roger Bacon, O.F.M. , also known as Doctor Mirabilis (Latin: "wonderful teacher"), was an English philosopher and Franciscan friar who placed considerable emphasis on empirical methods. He is sometimes credited as one of the earliest European advocates of the modern scientific method inspired by the works of Plato and Aristotle via early stated the times of full moons as a number of hours, minutes, seconds, thirds, and fourths (horae, minuta, secunda, tertia, and quarta) after noon on specified calendar dates.^[7] Although a third for ¹⁄₆₀ of a second remains in some languages, for example Polish Polish is a West Slavic language and the official language of Poland. Its written standard is the Polish alphabet which corresponds basically to the Latin alphabet with a few additions. Polish-speakers use the language in a uniform manner throughout most of Poland (tercja) and Turkish Turkish (Türkçe IPA [ˈt̪yɾktʃe] ) is spoken as a first language by over 77 million people worldwide, making it the most commonly spoken of the Turkic languages. Its speakers are located predominantly in Turkey and Cyprus, with smaller groups in Iraq, Greece, Bulgaria, the Republic of Macedonia, Kosovo, Albania and other parts of Eastern (salise), the modern second is subdivided decimally.

Seconds measured by mechanical clocks

In 1577 Taqi al-Din built a mechanical clock for the Istanbul observatory that had three dials showing hours, minutes, and seconds (marked every five seconds, not every second).^[8] The observatory and its instruments were destroyed in 1580. The first mechanical clock displaying seconds in Western Europe was constructed in Switzerland Switzerland , officially the Swiss Confederation (Confœderatio Helvetica in Latin, hence its ISO country codes CH and CHE), is a federal republic consisting of 26 cantons, with Bern as the seat of the federal authorities. The country is situated in Western Europe[note 4] where it is bordered by Germany to the north, France to the west, Italy to at the beginning of the 17th century.^[9]

The second first became accurately measurable with the development of pendulum clocks A pendulum clock is a clock that uses a pendulum, a swinging weight, as its timekeeping element. From its invention in 1656 by Christiaan Huygens until the 1930s, the pendulum clock was the world's most accurate timekeeper, accounting for its widespread use. Pendulum clocks must be stationary to operate; any motion or accelerations will affect the keeping mean time (as opposed to the apparent time displayed by sundials), specifically in 1670 when William Clement added a seconds pendulum A seconds pendulum is a pendulum whose period is precisely two seconds; one second for a swing in one direction and one second for the return swing to the original pendulum clock of Christian Huygens.^[10] The seconds pendulum has a period of two seconds, one second for a swing forward and one second for a swing back, enabling the longcase clock incorporating it to tick seconds. From this time, a second hand that rotated once per minute in a small subdial began to be added to the clock faces of precision clocks.

Show All>>

What Links Here:

Recently Viewed Pages:

• Ringtone
• Ringtone: Answers
• Home
• Referrers
• Ringtone
• Ringtone: Blogs
• Search Terms
• Images
• Ringtone: News
• News

Most Popular Pages:

• Sobrang Cheesy Quotes: Blogs
• Filet-o-Fish Ringtone: Blogs
• I465: Answers
• Hotlink Caller Ringtone
• Hotlink Caller Ringtone: Images
• Samsung Rant: Answers
• Sprint Promo Code: Answers
• Whistling Wizard Ringtone: Blogs
• Beckham: News
• Ventones: Answers

Related 'Second' Searches: