Second

Scheme of a pendulum clock with a period of oscillation of the pendulum of 2 seconds

The second (Russian designation: s ; international: s ) is a unit of time , one of the basic units of the International System of Units (SI) and the GHS system. In addition, it is a unit of time and refers to the number of basic units in the systems of the ISS , the ISSA , the MSCS , the MKSG , the MKSL , the MSC , the MSS , the IGSCD and the MTS ^[1] .

It is a time interval equal to 9,192,631,770 periods of radiation corresponding to the transition between two hyperfine levels of the ground state of the cesium-133 atom , which is at rest at 0 K. The exact text of the current definition of the second, approved by the XIII General Conference on Weights and Measures (GCMM) in 1967, is as follows ^[2] ^[3] :

The second is the time equal to 9,192,631,770 periods of radiation corresponding to the transition between two hyperfine levels of the ground state of the cesium-133 atom.

In 1997, the International Committee for Weights and Measures (CIPM) clarified that this definition refers to a cesium atom that is at rest at a temperature of 0 K ^[2] .

The term was borrowed in the 18th century from Latin, where secunda is an abbreviation of the expression pars minuta secunda - “small second part” ( hours ), unlike pars minuta prima - “small first part” (hours).

Content

Multiple and long units

With the unit of measure "second", as a rule, only long- term SI prefixes are used (except for deci- and centi-). The units of minute , hour , day , etc. are used to measure large time intervals.

Multiples				Dolny
magnitude	title	designation		magnitude	title	designation
10 ¹ s	decasecond	das	das	10 ⁻¹ s	decisecond	ds	ds
10 ² s	hectosecond	gf	hs	10 ⁻² s	centi second	ss	cs
10 ³ s	kilosecond	cc	ks	10 ⁻³ s	millisecond	ms	ms
10 ⁶ s	megasecond	Ms	Ms	10 ⁻⁶ s	microsecond	ms	µs
10 ⁹ s	gigasecond	Gs	Gs	10 ⁻⁹ s	nanosecond	ns	ns
10 ¹² s	terasecond	Tc	Ts	10 ⁻¹² s	picosecond	ps	ps
10 ¹⁵ s	petacecond	Ps	Ps	10 ⁻¹⁵ s	femtosecond	fs	fs
10 ¹⁸ s	ex-second	Es	Es	10 ⁻¹⁸ s	attosecond	ace	as
10 ²¹ s	zettasecond	ZS	Zs	10 ⁻²¹ s	zeptosecond	zs	zs
10 ²⁴ s	this second	Is	Ys	10 ⁻²⁴ s	octosecond	is	ys
not recommended not used or rarely used in practice

Equivalence to other time units

1 second equals:

1/60 minutes (also see the article Coordination Second )
1/3 600 hours
1/86 400 days ( MAC unit system)
1/31 557 600 Julian year (MAC system units)

Origin of title

The word second comes from the Latin phrase secunda divisio ^[4] . This means the second division of the hour (in the hexadecimal number system ).

History of second definitions

Before the advent of the mechanical clock

The inhabitants of ancient Egypt divided the day and night half of the day every 12 hours already, at least from 2000 BC. e. Due to the different durations of the night and day periods at different times of the year, the duration of the Egyptian hour was a variable value. The Greek astronomers of the Hellenistic Greece period Hipparch and Ptolemy divided the day based on the sixtieth decimal number system and also used the average hour ( ¹ ⁄ ₂₄ days) , simple fractions of an hour ( ¹ ⁄ ₄ , ² ⁄ ₃ , etc.) and time-degrees ( ¹ ⁄ ₃₆₀ days, or 4 modern minutes), but not modern minutes or seconds ^[5] .

In Babylonia, after 300 BC. e. the day was divided sixty, that is, 60, the resulting segment was another 60, then again 60, and so on, up to at least six digits after the hexadecimal separator (which gave an accuracy greater than two modern microseconds). For example, for the duration of their year, a 6-bit fractional number of the duration of one day was used, although they were not able to measure such a small gap physically. Another example is the defined synodic month duration, which was 29; 31,50,8,20 days (four fractional hex digits), which was repeated by Hipparch and Ptolemy and which is now the duration of the average synodic month in the Jewish calendar , although calculated as 29 days 12 hours and 793 heleks (where 1080 heleks are 1 hour) ^[6] . The Babylonians did not use the “hour” unit of time, instead it used a double hour with a duration of 120 modern minutes, as well as a time-degree with a duration of 4 minutes and a “third part” with a duration of 3 ¹ ₃ modern seconds ( helek in the modern Jewish calendar) ^[7] but they did not divide these smaller units. None of the sixty decimal parts of the day has ever been used as an independent unit of time.

In 1000, the Persian scientist Al-Biruni determined the times of the full moon for specific weeks in terms of the number of days, hours, minutes, seconds, thirds, and quarters, counting from Sunday noon ^[8] . In 1267, the English philosopher and naturalist Roger Bacon set the time intervals between full moons in the number of hours, minutes, seconds, thirds and quarters ( horae , minuta , secunda , tertia , quarta ) after noon of certain days ^[9] . Tertia - “third”, meaning “third division of an hour”, exists to designate ¹ ⁄ ₆₀ seconds and is now in some languages, for example Polish. tercja and tour. salise , however, this unit is underutilized and small periods of time are expressed in decimal fractions of a second (thousandth, millionth, etc.).

Seconds during mechanical clocks

The first known instance of a spring clock with a second hand is the clock of an unknown master with the image of Orpheus from the Fremersdorf collection, dated between 1560 and 1570 ^[10] ^[11] . In the 3rd quarter of the 16th century, the Ottoman encyclopaedist Takiyuddin ash-Shami created watches with marks every 1/5 minutes ^[12] . In 1579, Swiss watchmaker and instrument maker Jost Burgi designed a watch for Landgrave William IV , which showed seconds ^[10] . In 1581, the Danish scientist Tycho Brahe redesigned the clock in his observatory, which showed minutes, so that they began to show seconds. However, the mechanism was not yet sufficiently developed to measure the seconds with acceptable accuracy. In 1587, Tycho Brahe showed annoyance that the testimony of his four hours differed from each other by ± 4 seconds ^[10] . Measuring seconds with sufficient accuracy has become possible with the invention of a mechanical clock that allows you to maintain "average time" (as opposed to "relative time" shown by the sundial). In 1644, the French mathematician Maren Mersenne calculated that a pendulum with a length of 39.1 inches (0.994 m) will have a period of oscillations with standard gravity of exactly 2 seconds - 1 second to move forward and 1 second to move back, - allowing you to count accurate seconds

In 1670, the London watchmaker William Clement added such a second pendulum to the original pendulum clock of Christian Huygens ^[13] . From 1670 to 1680, Clemente improved his mechanism several times, after which he presented the watch cabinet he made to the public. In this watch, an anchor descent mechanism was used with a second pendulum showing seconds on a small auxiliary dial. Due to less friction, this mechanism required less energy than the previously used design of the whip trigger , and was precise enough to measure seconds as ¹ ⁄ ₆₀ minutes. For several years, the production of such watches was mastered by English watchmakers, and then spread to other countries. Thus, from now on, it was possible to measure seconds with proper accuracy.

Current measurements

As a unit of time, a second (meaning that an hour is divided into 60 two times, the first time is minutes, the second time is ( second ) - second) entered English at the end of the 17th century, about a hundred years before was measured with sufficient accuracy. Scientists and researchers who wrote in Latin, such as Roger Bacon , Tycho Brahe and Johann Kepler , used the Latin term secunda with the same meaning, starting from the 1200s.

In 1832, the German mathematician Karl Friedrich Gauss proposed to use the second as a basic unit of time in his system of units , which uses millimeter and milligram along with the second. The British Science Association ( Eng. British Science Association ) in 1862 ruled that "All scientists agreed to use the second average solar time as a unit of time" ( Eng. English time ^[14] ). The association developed the CGS system of units of measurement (centimeter-gram-second) in 1874, which over the next seventy years was gradually replaced by the ISS system (meter-kilogram-second). Both of these systems used the same second as the base unit. The ISS system received international application in the 1940s, and defined the second as 1/86400 average solar days .

In 1956, the definition of second was corrected and tied to the concept of “year” (the period of the Earth’s orbit around the Sun), taken for a specific epoch , since by that time it became known that the Earth’s rotation around its axis could not be used as a sufficiently reliable basis. in view of the fact that this rotation slows down, and also is subject to irregular jumps. The motion of the Earth was described in the tables of Newcomb ( eng. Newcomb's Tables of the Sun ) (1895), which proposed a formula for estimating the movement of the Sun for the 1900s, based on astronomical observations made between 1750 and 1892 ^[15] .

Thus, the second received the following definition:

"1/31 556 925,9747 the proportion of the tropical year for January 0, 1900 at 12 o'clock in the ephemeris time"
( Eng. the fraction 1 / 31,556,925.9747 for 1900 January 0 at 12 hours ephemeris time. ) ^[15]

This definition was adopted by the XI GKMV in 1960 ^[16] , at the same conference the International System of Units (SI) was approved as a whole.

The “ Tropical Year ” in the 1960 definition was not measured, but was calculated using a formula describing the average tropical year, which increases linearly over time. This corresponded to the scale of ephemeris time , adopted by the International Astronomical Union in 1952 ^[17] . This definition aligned the observed arrangement of celestial bodies with Newton's theory of their motion. In practice, for almost the entire twentieth century, the tables of Newcomb (from 1900 to 1983) and the tables of Ernest William Brown (from 1923 to 1983) were used ^[15] .

Thus, in 1960, the definition given in the SI system abolished any obvious connection between the second in scientific understanding and the length of the day, as most people understand it. With the invention of the atomic clock in the early 1960s, it was decided to use international atomic time as the basis for determining the second instead of the Earth’s revolution around the Sun. The basic principle of quantum mechanics is the indistinguishability of particles . Thus, while we do not take into account external influences, the structure of all atoms of a given isotope is completely identical. Therefore, they are ideal mechanisms that are reproduced at the request of the researcher with an accuracy limited only by the degree of influence of external influences. Therefore, the development of watches - keepers of time, led to the fact that the accuracy of the time scale implemented by atomic clocks exceeded the accuracy of astronomical determination, which also suffered from the impossibility of accurate reproducibility of the standard of a second. Therefore, it was decided to proceed to the realization of the second on the basis of the atomic clock, taking as a basis a transition in atoms weakly exposed to external influence. After discussion, it was decided to take cesium atoms, which have the additional advantage that cesium has only one stable isotope, and to compose a new definition of a second so that it most closely matches the ephemeris second used.

After several years of work, Lewis Essen from the National Physical Laboratory of Great Britain ( Teddington ( Eng. Teddington ), England) and William Markowitz ( Eng. William Markowitz ) from the US Naval Observatory determined the connection between the two superfine levels of the ground state of the cesium atom -133 with an ephemeris second ^[15] ^[18] . Using a method based on receiving signals from the WWV radio station (WWW (radio station) ) ^[19] , they determined the orbital motion of the moon around the earth, from which the motion of the sun could be determined in terms of time, measured by atomic clocks. They found that the second of ephemeris time has a duration of 9,192,631,770 ± 20 periods of cesium radiation ^[18] . As a result, in 1967, the XIII SCGM identified the second atomic time as:

FOCS 1, atomic clock in Switzerland with an error of 10 ⁻¹⁵ , that is, not more than a second in 30 million years

The second is the time equal to 9 192 631 770 periods of radiation corresponding to the transition between two hyperfine levels of the ground state of the cesium-133 atom. ^[15]

This second, referring to atomic time, was later checked for compliance with the second of the ephemeris time determined by lunar observations and coincided with it within 1 to 10 ¹⁰ ^[20] . Despite this, this second was already slightly shorter than the previous second, determined by the average solar time ^[21] ^[22] .

During the 1970s, it was discovered that the gravitational deceleration of time affects the seconds, measured by atomic clocks, depending on their elevation above the Earth's surface. The universal second was obtained by adjusting the values of each atomic clock by bringing them to mean sea level , thus extending the second by about 1⋅10 ⁻¹⁰ . This adjustment was made in 1977 and legalized in 1980 . In terms of the theory of relativity, the second of International Atomic Time is defined as the proper time on a rotating geoid ^[23] .

Later, in 1997, at the meeting of the International Committee of Measures and Weights, the definition of a second was clarified with the addition of the following definition ^[2] :

This definition refers to a cesium atom that is not perturbed by external fields at a temperature of 0 K.
( English This definition refers to a temperature of 0 K. )

The revised statement implies that an ideal atomic clock contains one cesium atom at rest, emitting a constant frequency wave. In practice, however, this definition means that high-precision measurements of a second must be refined, taking into account the external temperature ( blackbody radiation ) in which the atomic clock operates, and extrapolated to the value of a second at absolute zero .

Changes in the definitions of the basic units of the SI of 2018–2019 did not affect the second from the substantive point of view, but from stylistic considerations a formal definition was adopted ^[24] :

The second, denoted by c, is a unit of time in SI; its value is set by fixing the numerical value of the frequency of the hyperfine splitting of the ground state of the cesium-133 atom $\Delta \nu _{\text{Cs}}$ ${\ displaystyle \ Delta \ nu _ {\ text {Cs}}}$ equal to exactly 9,192,631,770 when it is expressed by the SI Hz unit, which is equivalent to ⁻¹ .

Notes

↑ Dengub V. M. , Smirnov V. G. Units of magnitude. Dictionary reference. - M .: Standards Publishing House, 1990. - p. 103. - 240 p. - ISBN 5-7050-0118-5 .
↑ ¹ ² ³ Unit of time (second) (English) . SI Brochure: The International System of Units (SI) . Bipm . The appeal date is October 9, 2015.
↑ Regulations on the units of quantities allowed for use in the Russian Federation (Unsolved) (inaccessible link) . Federal Information Foundation for ensuring uniformity of measurements . Rosstandart . The appeal date is February 28, 2018. Archived on September 18, 2017.
↑ Second // Physical Encyclopedia / Ch. ed. A. M. Prokhorov . - M .: Great Russian Encyclopedia , 1994. - T. 4. - p. 484. - 704 p. - 40 000 copies - ISBN 5-85270-087-8 .
↑ Toomer, GJ Ptolemy's Almagest. - Princeton, New Jersey: Princeton University Press, 1998. - P. 6–7, 23, 211–216. - ISBN 978-0-691-00260-6 .
↑ O Neugebauer . A history of ancient mathematical astronomy . - Springer-Verlag , 1975. - ISBN 0-387-06995-X .
↑ O Neugebauer . The astronomy of Maimonides and its sources (English) // Hebrew Union College College Annual : journal. - 1949. - Vol. 22 - P. 325 .
↑ al-Biruni. The Arabic version of the Athar-ul-Bakiya of the Albiruni, or "Vestiges of the Past" . - 1879. - P. 147–149.
↑ R Bacon. The Opus Majus of Roger Bacon. - University of Pennsylvania Press , 2000. - P. table facing page 231. - ISBN 978-1-85506-856-8 .
² ¹ ² ³ Landes, David S. Revolution in Time. - Cambridge, Massachusetts: Harvard University Press, 1983. - ISBN 0-674-76802-7 .
↑ Willsberger, Johann. Clocks & watches. - New York: Dial Press, 1975. - ISBN 0-8037-4475-7 . full page color photo: 4th caption page, 3rd photo thereafter (neither pages nor photos are numbered).
↑ Taqi al-Din
↑ Jessica Chappell. The Long Case Clock: Into a Grandfather Clock (English) // Illumin: journal. - 2001. - 1 October ( vol. 1 , no. 0 ). - P. 1 .
↑ Reports of the committee on electrical standards (Neopr.) . British Association for the Advancement of Science (1873).
↑ ¹ ² ³ ⁴ ⁵ Leap Seconds . Time Service Department, United States Naval Observatory . The appeal date was December 31, 2006. Archived May 27, 2012.
↑ Resolution 9 of the XI General Conference on Weights and Measures (1960) (English)
↑ Explanatory Supplement to the Astronomical Ephemeris and the American Ephemeris and Nautical Almanac (prepared jointly by the United States of America, HMSO, London, 1961), at Sect. 1C, p.9), stating the astronomy of the astronomy ... this was a meeting with the solar ephemeris in terms of ephemeris time. These recommendations were formally adopted in September 1952. ”
↑ ¹ ² W Markowitz, RG Hall, L Essen, JVL Parry. Frequency of cesium in terms of ephemeris time (Neopr.) // Physical Review Letters . - 1958. - V. 1 , № 3 . - pp . 105-107 . - DOI : 10.1103 / PhysRevLett.1.105 . - .
↑ S Leschiutta. The definition of the 'atomic' second (Neopr.) // . - 2005. - Vol. 42 , No. 3 . - S. S10 — S19 . - DOI : 10.1088 / 0026-1394 / 42/3 / S03 . - .
↑ W Markowitz (1988). "{{{title}}}" in IAU Sumposia # 128 . The Earth's Rotation and Reference Frames for Geodesy and Geophysics : 413–418.
↑ DD McCarthy, C Hackman, R Nelson. The Physical Basis of the Leap Second (English) // The Astronomical Journal . - IOP Publishing , 2008. - Vol. 136 , no. 5 - P. 1906-1908 . - DOI : 10.1088 / 0004-6256 / 136/5/1906 . - .
Solar solar solar solar solar U U U U U U U ( 2 2 ) ± 20 cycles ), see L Essen. Time Scales (Neopr.) // . - 1968. - V. 4 , № 4 . - p . 161-165 . - DOI : 10.1088 / 0026-1394 / 4/4/003 . - . . As noted in page 162, the 9 192 631 770 figure was chosen for the SI second. L Essen in the same 1968 article stated that this value "seemed to be in UT2".
↑ See page 515 in RA Nelson; McCarthy, DD; Malys, S; Levine, J; Guinot, B; Fliegel, HF; Beard, RL; Bartholomew, T R. et al. The leap second: its history and possible future (Neopr.) // . - 2000. - V. 38 , № 6 . - p . 509-529 . - DOI : 10.1088 / 0026-1394 / 38/6/6 . - .
↑ SI base units (Unc.) . Bipm . The appeal date is June 22, 2019.

Literature

Time and frequency (collection of articles), edited by D. Jespersen and others, translated from English, M., 1973.

Links

Second (unit of time) / N. S. Blinov // Great Soviet Encyclopedia : [in 30 tons.] / Ch. ed. A. M. Prokhorov . - 3rd ed. - M .: Soviet Encyclopedia, 1969-1978.
National Physical Laboratory: Trapped ion optical frequency standards
High-accuracy strontium ion optical clock ; National Physical Laboratory (2005)
National Research Council of Canada: single trapped ion (inaccessible link from 21-05-2013 [2257 days] - history , copy )
NIST: Definition of the second ; notice the cesium atom must be in its ground state at 0 K
Official BIPM definition of the second
Seconds and leap seconds by the usno
The leap second: its history and possible future
What is a Cesium atom clock? (inaccessible link from 21-05-2013 [2257 days] - history , copy )

[Деньгуб-1] Dengub V. M. , Smirnov V. G. Units of magnitude. Dictionary reference. - M .: Standards Publishing House, 1990. - p. 103. - 240 p. - ISBN 5-7050-0118-5 .

[Second-2] ¹ ² ³ Unit of time (second) (English) . SI Brochure: The International System of Units (SI) . Bipm . The appeal date is October 9, 2015.

[Положение-3] Regulations on the units of quantities allowed for use in the Russian Federation (Unsolved) (inaccessible link) . Federal Information Foundation for ensuring uniformity of measurements . Rosstandart . The appeal date is February 28, 2018. Archived on September 18, 2017.

[4] Second // Physical Encyclopedia / Ch. ed. A. M. Prokhorov . - M .: Great Russian Encyclopedia , 1994. - T. 4. - p. 484. - 704 p. - 40 000 copies - ISBN 5-85270-087-8 .

[5] Toomer, GJ Ptolemy's Almagest. - Princeton, New Jersey: Princeton University Press, 1998. - P. 6–7, 23, 211–216. - ISBN 978-0-691-00260-6 .

[6] O Neugebauer . A history of ancient mathematical astronomy . - Springer-Verlag , 1975. - ISBN 0-387-06995-X .

[7] O Neugebauer . The astronomy of Maimonides and its sources (English) // Hebrew Union College College Annual : journal. - 1949. - Vol. 22 - P. 325 .

[al-Biruni-8] al-Biruni. The Arabic version of the Athar-ul-Bakiya of the Albiruni, or "Vestiges of the Past" . - 1879. - P. 147–149.

[9] R Bacon. The Opus Majus of Roger Bacon. - University of Pennsylvania Press , 2000. - P. table facing page 231. - ISBN 978-1-85506-856-8 .

[Landes-10] ² ¹ ² ³ Landes, David S. Revolution in Time. - Cambridge, Massachusetts: Harvard University Press, 1983. - ISBN 0-674-76802-7 .

[11] Willsberger, Johann. Clocks & watches. - New York: Dial Press, 1975. - ISBN 0-8037-4475-7 . full page color photo: 4th caption page, 3rd photo thereafter (neither pages nor photos are numbered).

[12] Taqi al-Din

[13] Jessica Chappell. The Long Case Clock: Into a Grandfather Clock (English) // Illumin: journal. - 2001. - 1 October ( vol. 1 , no. 0 ). - P. 1 .

[14] Reports of the committee on electrical standards (Neopr.) . British Association for the Advancement of Science (1873).

[USNO-15] ¹ ² ³ ⁴ ⁵ Leap Seconds . Time Service Department, United States Naval Observatory . The appeal date was December 31, 2006. Archived May 27, 2012.

[16] Resolution 9 of the XI General Conference on Weights and Measures (1960) (English)

[17] Explanatory Supplement to the Astronomical Ephemeris and the American Ephemeris and Nautical Almanac (prepared jointly by the United States of America, HMSO, London, 1961), at Sect. 1C, p.9), stating the astronomy of the astronomy ... this was a meeting with the solar ephemeris in terms of ephemeris time. These recommendations were formally adopted in September 1952. ”

[mark58-18] ¹ ² W Markowitz, RG Hall, L Essen, JVL Parry. Frequency of cesium in terms of ephemeris time (Neopr.) // Physical Review Letters . - 1958. - V. 1 , № 3 . - pp . 105-107 . - DOI : 10.1103 / PhysRevLett.1.105 . - .

[19] S Leschiutta. The definition of the 'atomic' second (Neopr.) // . - 2005. - Vol. 42 , No. 3 . - S. S10 — S19 . - DOI : 10.1088 / 0026-1394 / 42/3 / S03 . - .

[20] W Markowitz (1988). "{{{title}}}" in IAU Sumposia # 128 . The Earth's Rotation and Reference Frames for Geodesy and Geophysics : 413–418.

[21] DD McCarthy, C Hackman, R Nelson. The Physical Basis of the Leap Second (English) // The Astronomical Journal . - IOP Publishing , 2008. - Vol. 136 , no. 5 - P. 1906-1908 . - DOI : 10.1088 / 0004-6256 / 136/5/1906 . - .

[22] Solar solar solar solar solar U U U U U U U ( 2 2 ) ± 20 cycles ), see L Essen. Time Scales (Neopr.) // . - 1968. - V. 4 , № 4 . - p . 161-165 . - DOI : 10.1088 / 0026-1394 / 4/4/003 . - . . As noted in page 162, the 9 192 631 770 figure was chosen for the SI second. L Essen in the same 1968 article stated that this value "seemed to be in UT2".

[23] See page 515 in RA Nelson; McCarthy, DD; Malys, S; Levine, J; Guinot, B; Fliegel, HF; Beard, RL; Bartholomew, T R. et al. The leap second: its history and possible future (Neopr.) // . - 2000. - V. 38 , № 6 . - p . 509-529 . - DOI : 10.1088 / 0026-1394 / 38/6/6 . - .

[24] SI base units (Unc.) . Bipm . The appeal date is June 22, 2019.