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Celsius

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"Centigrade" redirects here. For other uses, seeCelsius (disambiguation)andCentigrade (disambiguation).

degree Celsius
Athermometercalibrated in degrees Celsius, showing a temperature of −17 °C
General information
Unit systemSI
Unit oftemperature
Symbol°C
Named afterAnders Celsius
Conversions
x°Cin...... corresponds to...
SI base units(x+ 273.15)K
Imperial/USunits(⁠9/5⁠x+ 32)°F

Thedegree Celsiusis the unit oftemperatureon theCelsius temperature scale[1](originally known as thecentigrade scaleoutside Sweden),[2]one of twotemperature scalesused in theInternational System of Units(SI), the other being the closely relatedKelvin scale.The degree Celsius (symbol:°C) can refer to a specific point on the Celsius temperature scale or to a difference or range between two temperatures. It is named after the Swedish astronomerAnders Celsius(1701–1744), who proposed the first version of it in 1742. The unit was calledcentigradein several languages (from the Latincentum,which means 100, andgradus,which means steps) for many years. In 1948, theInternational Committee for Weights and Measures[3]renamed it to honor Celsius and also to remove confusion with the term for one hundredth of agradianin some languages. Most countries use this scale (theFahrenheitscale is still used in the United States, some island territories, andLiberia).

Throughout the 19th century, the scale was based on 0 °C for the freezing point of water and 100 °C for the boiling point of water at 1atmpressure. (In Celsius's initial proposal, the values were reversed; the boiling point was 0 degrees and the freezing point was 100 degrees).

Between 1954 and 2019, the precise definitions of the unitdegree Celsiusand the Celsius temperature scale used absolute zero and thetriple pointof water. Since 2007, the Celsius temperature scale has been defined in terms of thekelvin,theSI base unitofthermodynamic temperature(symbol: K). Absolute zero, the lowest temperature, is now defined as being exactly 0 K and −273.15 °C.[4]

Countries by usage
Celsius (°C)
Celsius (°C) and Fahrenheit (°F)
Fahrenheit (°F)

History[edit]

Anders Celsius's original thermometer used a reversed scale, with 100 as the freezing point and 0 as the boiling point of water.

In 1742, Swedish astronomerAnders Celsius(1701–1744) created a temperature scale that was the reverse of the scale now known as "Celsius": 0 represented the boiling point of water, while 100 represented the freezing point of water.[5]In his paperObservations of two persistent degrees on a thermometer,he recounted his experiments showing that the melting point of ice is essentially unaffected by pressure. He also determined with remarkable precision how the boiling point of water varied as a function of atmospheric pressure. He proposed that the zero point of his temperature scale, being the boiling point, would be calibrated at the mean barometric pressure at mean sea level. This pressure is known as onestandard atmosphere.TheBIPM's 10thGeneral Conference on Weights and Measures(CGPM) in 1954 defined one standard atmosphere to equal precisely 1,013,250dynesper square centimeter (101.325kPa).[6]

In 1743, theLyonnaisphysicistJean-Pierre Christin,permanent secretary of theAcademy of Lyon,inverted the Celsius temperature scale so that 0 represented the freezing point of water and 100 represented the boiling point of water. Some credit Christin for independently inventing the reverse of Celsius's original scale, while others believe Christin merely reversed Celsius's scale.[7][8]On 19 May 1743 he published the design of amercury thermometer,the "Thermometer of Lyon" built by the craftsman Pierre Casati that used this scale.[9][10][11]

In 1744, coincident with the death of Anders Celsius, the Swedish botanistCarl Linnaeus(1707–1778) reversed Celsius's scale.[12]His custom-made "Linnaeus-thermometer", for use in his greenhouses, was made by Daniel Ekström, Sweden's leading maker of scientific instruments at the time, whose workshop was located in the basement of the Stockholm observatory. As often happened in this age before modern communications, numerous physicists, scientists, and instrument makers are credited with having independently developed this same scale;[13]among them were Pehr Elvius, the secretary of the Royal Swedish Academy of Sciences (which had an instrument workshop) and with whom Linnaeus had been corresponding;Daniel Ekström[sv],the instrument maker; and Mårten Strömer (1707–1770) who had studied astronomy under Anders Celsius.

The first known Swedish document[14]reporting temperatures in this modern "forward" Celsius temperature scale is the paperHortus Upsaliensisdated 16 December 1745 that Linnaeus wrote to a student of his, Samuel Nauclér. In it, Linnaeus recounted the temperatures inside the orangery at theUniversity of Uppsala Botanical Garden:

...since the caldarium (the hot part of the greenhouse) by the angle of the windows, merely from the rays of the sun, obtains such heat that the thermometer often reaches 30 degrees, although the keen gardener usually takes care not to let it rise to more than 20 to 25 degrees, and in winter not under 15 degrees...

"Centigrade" versus "Celsius"[edit]

Since the 19th century, the scientific andthermometrycommunities worldwide have used the phrase "centigrade scale" and temperatures were often reported simply as "degrees" or, when greater specificity was desired, as "degrees centigrade", with the symbol °C.

In the French language, the termcentigradealso means one hundredth of agradian,when used forangular measurement.The termcentesimal degreewas later introduced for temperatures[15]but was also problematic, as it means gradian (one hundredth of a right angle) in the French and Spanish languages. The risk of confusion between temperature and angular measurement was eliminated in 1948 when the 9th meeting of theGeneral Conference on Weights and Measuresand the Comité International des Poids et Mesures (CIPM) formally adopted "degree Celsius" for temperature.[16][a]

While "Celsius" is commonly used in scientific work, "centigrade" is still used in French and English-speaking countries, especially in informal contexts, albeit less and less.[17]

While inAustraliafrom 1 September 1972, only Celsius measurements were given for temperature in weather reports/forecasts.[18]It was not until February 1985 that theweather forecasts issued by the BBCswitched from "centigrade" to "Celsius".[19]

Common temperatures[edit]

Equivalent temperatures in kelvin (K), Rankine (R), Celsius (°C), and Fahrenheit (°F)

All phase transitions are atstandard atmosphere.Figures are either by definition, or approximated from empirical measurements.

Key temperature scale relations
Kelvin Celsius Fahrenheit Rankine
Absolute zero[A] 0 K −273.15 °C −459.67 °F 0 °R
Intersection of Celsius andFahrenheitscales[A] 233.15 K −40 °C −40 °F 419.67 °R
Boiling point of water[b] 373.1339 K 99.9839 °C 211.971 °F 671.6410 °R
Boiling point ofliquid nitrogen 77.4 K −195.8 °C[20] −320.4 °F 139.3 °R
Melting point of ice[21] 273.1499 K −0.0001 °C 31.9998 °F 491.6698 °R
Sublimationpoint ofdry ice 195.1 K −78 °C −108.4 °F 351.2 °R
Commonroom temperature[B][22] 293 K 20 °C 68 °F 528 °R
Averagenormal human body temperature[23] 310.15 K 37.0 °C 98.6 °F 558.27 °R
  1. ^abExact value, by SI definition of the kelvin
  2. ^NIST common reference temperature, provided as round numbers

Name and symbol typesetting[edit]

The "degree Celsius" has been the onlySI unitwhose full unit name contains an uppercase letter since 1967, when theSI base unitfor temperature became thekelvin,replacing the capitalized termdegrees Kelvin.The plural form is "degrees Celsius".[24]

The general rule of theInternational Bureau of Weights and Measures(BIPM) is that the numerical value always precedes the unit, and a space is always used to separate the unit from the number,e.g. "30.2 °C"(not "30.2°C" or "30.2° C" ).[25]The only exceptions to this rule are for the unitsymbols for degree,minute, and second for plane angle (°,′,and ″, respectively), for which no space is left between the numerical value and the unit symbol.[26]Other languages, and various publishing houses, may follow different typographical rules.

Unicode character[edit]

Unicodeprovides the Celsius symbol at code pointU+2103℃DEGREE CELSIUS.However, this is acompatibility characterprovided forroundtrip compatibilitywith legacy encodings. It easily allows correct rendering for vertically written East Asian scripts, such as Chinese. The Unicode standard explicitly discourages the use of this character: "In normal use, it is better to represent degrees Celsius '°C' with a sequence ofU+00B0°DEGREE SIGN+U+0043CLATIN CAPITAL LETTER C,rather thanU+2103℃DEGREE CELSIUS.For searching, treat these two sequences as identical. "[27]

Temperatures and intervals[edit]

The degree Celsius is subject to the same rules as the kelvin with regard to the use of its unit name and symbol. Thus, besides expressing specific temperatures along its scale (e.g. "Galliummelts at 29.7646 °C "and" The temperature outside is 23 degrees Celsius "), the degree Celsius is also suitable for expressing temperatureintervals:differences between temperatures or their uncertainties (e.g. "The output of the heat exchanger is hotter by 40 degrees Celsius", and "Our standard uncertainty is ±3 °C" ).[28]Because of this dual usage, one must not rely upon the unit name or its symbol to denote that a quantity is a temperature interval; it must be unambiguous through context or explicit statement that the quantity is an interval.[c]This is sometimes solved by using the symbol °C (pronounced "degrees Celsius" ) for a temperature, and C° (pronounced "Celsius degrees" ) for a temperature interval, although this usage is non-standard.[29]Another way to express the same is"40 °C ± 3 K",which can be commonly found in literature.

Celsius measurement follows aninterval systembut not aratio system;and it follows a relative scale not an absolute scale. For example, an object at 20 °C does not have twice the energy of when it is 10 °C; and 0 °C is not the lowest Celsius value. Thus, degrees Celsius is a useful interval measurement but does not possess the characteristics of ratio measures like weight or distance.[30]

Coexistence with Kelvin[edit]

In science and in engineering, the Celsius and Kelvin scales are often used in combination in close contexts, e.g. "a measured value was 0.01023 °C with an uncertainty of 70 μK". This practice is permissible because the magnitude of the degree Celsius is equal to that of the kelvin. Notwithstanding the official endorsement provided by decision no. 3 of Resolution 3 of the 13th CGPM,[31]which stated "a temperature interval may also be expressed in degrees Celsius", the practice of simultaneously using both °C and K remains widespread throughout the scientific world as the use ofSI-prefixedforms of the degree Celsius (such as "μ°C" or "microdegrees Celsius" ) to express a temperature interval has not been widely adopted.

Melting and boiling points of water[edit]

Celsius temperature conversion formulae
from Celsius to Celsius
Fahrenheit x°C ≘ (x×⁠9/5⁠+ 32) °F x°F ≘ (x− 32) ×⁠5/9⁠°C
Kelvin x°C ≘ (x+ 273.15) K xK ≘ (x− 273.15) °C
Rankine x°C ≘ (x+ 273.15) ×⁠9/5⁠°R x°R ≘ (x− 491.67) ×⁠5/9⁠°C
For temperatureintervalsrather than specific temperatures,
1 °C = 1 K =⁠9/5⁠°F =⁠9/5⁠°R
Conversion between temperature scales

The melting and boiling points of water are no longer part of the definition of the Celsius temperature scale. In 1948, the definition was changed to use thetriple point of water.[32]In 2005 the definition was further refined to use water with precisely defined isotopic composition (VSMOW) for the triple point. In 2019, the definition was changed to use theBoltzmann constant,completely decoupling the definition of the kelvin from theproperties of water.Each of these formal definitions left the numerical values of the Celsius temperature scale identical to the prior definition to within the limits of accuracy of themetrologyof the time.

When the melting and boiling points of water ceased being part of the definition, they became measured quantities instead. This is also true of the triple point.

In 1948 when the 9th General Conference on Weights and Measures (CGPM) in Resolution 3 first considered using the triple point of water as a defining point, the triple point was so close to being 0.01 °C greater than water's known melting point, it was simply defined as precisely 0.01 °C. However, later measurements showed that the difference between the triple and melting points of VSMOW is actually very slightly (< 0.001 °C) greater than 0.01 °C. Thus, the actual melting point of ice is very slightly (less than a thousandth of a degree) below 0 °C. Also, defining water's triple point at 273.16 K precisely defined the magnitude of each 1 °C increment in terms of theabsolute thermodynamic temperature scale(referencing absolute zero). Now decoupled from the actual boiling point of water, the value "100 °C" is hotter than 0 °C – in absolute terms – by a factor ofexactly⁠373.15/273.15⁠(approximately 36.61% thermodynamically hotter). When adheringstrictlyto the two-point definition for calibration, the boiling point of VSMOW under one standard atmosphere of pressure was actually 373.1339 K (99.9839 °C). When calibrated toITS-90(a calibration standard comprising many definition points and commonly used for high-precision instrumentation), the boiling point of VSMOW was slightly less, about 99.974 °C.[33]

This boiling-point difference of 16.1 millikelvins between the Celsius temperature scale's original definition and the previous one (based on absolute zero and the triple point) has little practical meaning in common daily applications because water's boiling point is very sensitive to variations inbarometric pressure.For example, an altitude change of only 28 cm (11 in) causes the boiling point to change by one millikelvin.

See also[edit]

Notes[edit]

  1. ^According toThe Oxford English Dictionary(OED), the term "Celsius thermometer" had been used at least as early as 1797. Further, the term "The Celsius or Centigrade thermometer" was again used in reference to a particular type of thermometer at least as early as 1850. The OED also cites this 1928 reporting of a temperature: "My altitude was about 5,800 metres, the temperature was 28° Celsius." However, dictionaries seek to find the earliest use of a word or term and are not a useful resource as regards to the terminology used throughout the history of science. According to several writings ofTerry Quinn,Director of the BIPM (1988–2004), including"Temperature Scales from the early days of thermometry to the 21st century"(PDF).Archived fromthe original(PDF)on 26 December 2010.Retrieved31 May2016.(146KiB)as well asTemperature(2nd Edition/1990/Academic Press/0125696817), the termCelsiusin connection with the centigrade scale was not used whatsoever by the scientific or thermometry communities until after the CIPM and CGPM adopted the term in 1948. The BIPM was not even aware that "degree Celsius" was in sporadic, non-scientific use before that time. It is also noteworthy that the twelve-volume, 1933 edition of OED didn't even have a listing for the wordCelsius(but did have listings for bothcentigradeandcentesimalin the context of temperature measurement). The 1948 adoption ofCelsiusaccomplished three objectives:
    1. All common temperature scales would have their units named after someone closely associated with them; namely, Kelvin, Celsius, Fahrenheit, Réaumur and Rankine.
    2. Notwithstanding the important contribution of Linnaeus who gave the Celsius temperature scale its modern form, Celsius's name was the obvious choice because it began with the letter C. Thus, the symbol °C that for centuries had been used in association with the namecentigradecould remain in use and would simultaneously inherit an intuitive association with the new name.
    3. The new name eliminated the ambiguity of the term "centigrade", freeing it to refer exclusively to the French-language name for the unit of angular measurement.
  2. ^ForVienna Standard Mean Ocean Waterat onestandard atmosphere(101.325 kPa) when calibrated solely per the two-point definition of thermodynamic temperature. Older definitions of the Celsius temperature scale once defined the boiling point of water under one standard atmosphere as being precisely 100 °C. However, the current definition results in a boiling point that is actually 16.1 mK less. For more about the actual boiling point of water, seeVSMOW in temperature measurement.A different approximation usesITS-90,which approximates the temperature to 99.974 °C
  3. ^In 1948,Resolution 7 of the 9th CGPMstated,"To indicate a temperature interval or difference, rather than a temperature, the word 'degree' in full, or the abbreviation 'deg' must be used."This resolution was abrogated in 1967/1968 byResolution 3 of the 13th CGPM,which stated that[ "The names" degree Kelvin "and" degree ", the symbols" °K "and" deg "and the rules for their use given in Resolution 7 of the 9th CGPM (1948),]...and the designation of the unit to express an interval or a difference of temperatures are abrogated, but the usages which derive from these decisions remain permissible for the time being."Consequently, there is now wide freedom in usage regarding how to indicate a temperature interval. The most important thing is that one's intention must be clear and the basic rule of the SI must be followed; namely that the unit name or its symbol must not be relied upon to indicate the nature of the quantity. Thus, if a temperature interval is, say, 10 K or 10 °C (which may be written 10 kelvins or 10 degrees Celsius), it must be unambiguous through obvious context or explicit statement that the quantity is an interval. Rules governing the expressing of temperatures and intervals are covered in the BIPM's"SI Brochure, 8th edition"(PDF).(1.39MiB).

References[edit]

  1. ^Celsius temperature scaleat theEncyclopædia Britannica"Celsius temperature scale, also called centigrade temperature scale, scale based on 0 ° for the melting point of water and 100 ° for the boiling point of water at 1 atm pressure."
  2. ^Helmenstine, Anne Marie (15 December 2014)."What Is the Difference Between Celsius and Centigrade?".thoughtco.Archivedfrom the original on 27 November 2023.Retrieved25 April2020.
  3. ^"Proceedings of the 42nd CIPM (1948), 1948, p. 88".Bureau International des Poids et Mesures. 1948.Retrieved19 August2023.
  4. ^"SI brochure, section 2.1.1.5".International Bureau of Weights and Measures.Archived fromthe originalon 26 September 2007.Retrieved9 May2008.
  5. ^Celsius, Anders (1742)."Observationer om twänne beständiga grader på en thermometer"[Observations about two stable degrees on a thermometer].Kungliga Svenska Vetenskapsakademiens Handlingar (Proceedings of the Royal Swedish Academy of Sciences)(3): 171–180 andFig. 1.
  6. ^Resolution 4 of the 10th meeting of the CGPM - Definition of the standard atmosphere (Report). 1954.doi:10.59161/CGPM1954RES4E.hdl:2060/19930080725.
  7. ^Rittner, D.;Bailey, R.A. (2014).Encyclopedia of Chemistry.Facts on File Science Dictionary. Facts On File, Incorporated. p. 43.ISBN978-1-4381-1002-8.
  8. ^Smith, Jacqueline (2009)."Appendix I: Chronology".The Facts on File Dictionary of Weather and Climate.Infobase Publishing. p. 246.ISBN978-1-4381-0951-0.1743 Jean-Pierre Christin inverts the fixed points on Celsius' scale, to produce the scale used today.
  9. ^"MEMOIRE sur la dilatation du Mercure dans le Thermométre".Mercure de France(in French). Paris: Chaubert; Jean de Nully, Pissot, Duchesne: 1609–1610. 1743.
  10. ^Journal helvétique(1743):LION.Imprimerie des Journalistes,Neuchâtel.pp. 308–310.
  11. ^Memoires pour L'Histoire des Sciences et des Beaux Arts(1743):DE LYON.Chaubert, París. pp. 2125–2128.
  12. ^Citation: Uppsala University (Sweden),Linnaeus' thermometer
  13. ^Citation for Christin of Lyons: Le Moyne College,Glossary, (Celsius scale);citation for Linnaeus's connection with Pehr Elvius and Daniel Ekström: Uppsala University (Sweden),Linnaeus' thermometer;general citation: The Uppsala Astronomical Observatory,History of the Celsius temperature scaleArchived22 July 2009 at theWayback Machine
  14. ^Citations: University of Wisconsin–Madison,Linnæus & his Gardenand; Uppsala University,Linnaeus' thermometer
  15. ^Comptes rendus des séances de la cinquième conférence générale des poids et mesures, réunie à Paris en 1913.Bureau international des poids et mesures. 1913. pp. 55, 57, 59.Retrieved10 June2021.p. 60:...à la température de 20° centésimaux
  16. ^"CIPM, 1948 and 9th CGPM, 1948".International Bureau of Weights and Measures.Archived fromthe originalon 5 April 2021.Retrieved9 May2008.
  17. ^"centigrade, adj. and n."Oxford English Dictionary.Oxford University Press.Retrieved20 November2011.
  18. ^"Temperature and Pressure go Metric"(PDF).Commonwealth Bureau of Meteorology. 1 September 1972.Retrieved16 February2022.
  19. ^1985 BBC Special: A Change In The WeatheronYouTube
  20. ^Lide, D.R., ed. (1990–1991).Handbook of Chemistry and Physics.71st ed. CRC Press. p. 4–22.
  21. ^The ice point of purified water has been measured at0.000089(10)degrees Celsius – seeMagnum, B.W. (June 1995)."Reproducibility of the Temperature of the Ice Point in Routine Measurements"(PDF).NIST Technical Note.1411.Archived fromthe original(PDF)on 10 July 2007.Retrieved11 February2007.
  22. ^"SI Units – Temperature".NIST Office of Weights and Measures. 2010.Retrieved21 July2022.
  23. ^Elert, Glenn (2005)."Temperature of a Healthy Human (Body Temperature)".The Physics Factbook.Retrieved22 August2007.
  24. ^"Unit of thermodynamic temperature (kelvin)".The NIST Reference on Constants, Units, and Uncertainty: Historical context of the SI.National Institute of Standards and Technology (NIST).2000. Archived fromthe originalon 11 November 2004.Retrieved16 November2011.
  25. ^BIPM,SI Brochure,Section 5.3.3.
  26. ^For more information on conventions used in technical writing, see the informativeSI Unit rules and style conventionsby theNISTas well as theBIPM's SI brochure: Subsection 5.3.3,Formatting the value of a quantity.Archived5 July 2014 at theWayback Machine
  27. ^"22.2".The Unicode Standard, Version 9.0(PDF).Mountain View, CA, USA: The Unicode Consortium. July 2016.ISBN978-1-936213-13-9.Retrieved20 April2017.
  28. ^Decision No. 3 ofResolution 3 of the 13th CGPM.
  29. ^H.D. Young, R. A. Freedman (2008). University Physics with Modern Physics (12th ed.). Addison Wesley. p. 573.
  30. ^This fact is demonstrated in the bookBiostatistics: A Guide to Design, Analysis, and DiscoveryBy Ronald N. Forthofer, Eun Sul Lee and Mike Hernandez
  31. ^"Resolution 3 of the 13th CGPM (1967)".
  32. ^"Resolution 3 of the 9th CGPM (1948)".International Bureau of Weights and Measures.Retrieved6 February2024.
  33. ^Citation: London South Bank University,Water Structure and Behavior, notes c1 and c2

External links[edit]

The dictionary definition ofCelsiusat Wiktionary

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