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The Celsius
Celsius
scale, previously known as the centigrade scale,[1][2] is a temperature scale used by the International System of Units
International System of Units
(SI). As an SI derived unit, it is used by all countries in the world, except the United States, Myanmar, and Liberia. It is named after the Swedish astronomer Anders Celsius
Anders Celsius
(1701–1744), who developed a similar temperature scale. The degree Celsius
Celsius
(symbol: °C) can refer to a specific temperature on the Celsius
Celsius
scale as well as a unit to indicate a temperature interval, a difference between two temperatures or an uncertainty. Before being renamed to honor Anders Celsius
Anders Celsius
in 1948, the unit was called centigrade, from the Latin centum, which means 100, and gradus, which means steps. Before 1954, the Celsius
Celsius
scale was based on 0 °C for the freezing point of water and 100 °C for the boiling point of water at 1 atm pressure following a change introduced in 1743 by Jean-Pierre Christin
Jean-Pierre Christin
to reverse the Celsius
Celsius
thermometer scale (from water boiling at 0 degrees and ice melting at 100 degrees). This scale is widely taught in schools today. By international agreement, since 1954 the unit "degree Celsius" and the Celsius
Celsius
scale are defined by absolute zero and the triple point of Vienna Standard Mean Ocean Water
Vienna Standard Mean Ocean Water
(VSMOW), a specially purified water. This definition also precisely relates the Celsius
Celsius
scale to the Kelvin scale, which defines the SI base unit
SI base unit
of thermodynamic temperature with symbol K. Absolute zero, the lowest temperature possible, is defined as being exactly 0 K and −273.15 °C. The temperature of the triple point of water is defined as exactly 273.16 K (0.01 °C; 32.02 °F).[3] Thus, a temperature difference of one degree Celsius
Celsius
and that of one kelvin is exactly the same, with the null point of the Kelvin
Kelvin
scale (0 K) at exactly −273.15 °C, and the null point of the Celsius
Celsius
scale (0 °C) at exactly 273.15 K.[4]

Contents

1 History

1.1 Centigrade, hectograde and Celsius 1.2 Common temperatures

2 Name and symbol typesetting

2.1 Unicode
Unicode
character

3 Temperatures and intervals 4 Coexistence of Kelvin
Kelvin
and Celsius
Celsius
scales 5 Melting and boiling points of water 6 See also 7 Notes 8 References 9 External links

History[edit]

An illustration of Anders Celsius's original thermometer. Note the reversed scale, where 100 is the freezing point of water and 0 is its boiling point.

In 1742, Swedish astronomer Anders Celsius
Anders Celsius
(1701–1744) created a temperature scale which was the reverse of the scale now known by the name "Celsius": 0 represented the boiling point of water, while 100 represented the freezing point of water.[5] In his paper Observations 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 one standard atmosphere. The BIPM's 10th General Conference on Weights and Measures (CGPM) later defined one standard atmosphere to equal precisely 1013250dynes per square centimetre (101.325 kPa).[6] In 1743, the Lyonnais physicist Jean-Pierre Christin, permanent secretary of the Académie des sciences, belles-lettres et arts de LyonFR, working independently of Celsius, developed a scale where zero represented the freezing point of water and 100 represented the boiling point of water.[7][8] On 19 May 1743 he published the design of a mercury thermometer, the " Thermometer
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 botanist Carl Linnaeus
Carl 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 and 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
Celsius
scale is the paper Hortus Upsaliensis dated 16 December 1745 that Linnaeus wrote to a student of his, Samuel Nauclér. In it, Linnaeus recounted the temperatures inside the orangery at the University 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, hectograde and Celsius[edit] Since the 19th century, the scientific and thermometry communities worldwide referred to this scale as the centigrade scale. Temperatures on the centigrade scale were often reported simply as degrees or, when greater specificity was desired, as degrees centigrade (symbol: °C). Because the term centigrade was also the Spanish and French language name for a unit of angular measurement (1/10000 of a right angle) and had a similar connotation in other languages, the term centesimal degree (known as the gradian, "grad" or "gon": 1ᵍ = 0.9°, 100ᵍ = 90°) was used when very precise, unambiguous language was required by international standards bodies such as the BIPM. More properly, what was defined as "centigrade" then would now be "hectograde". Furthermore, in the context here, centigrade/hectograde is referring to the whole 0–100 range, not the given part thereof, hence "20° centigrade" means "20ᵍ per 100 gradians" (or 20% hectograde), not its literal description, "0.2 gradians".

(To be descriptively correct, "20° centigrade" should be "20° hectocentigrade", or just "20 gradians" 20ᵍ .)

To eliminate such confusion, the 9th CGPM and the CIPM (Comité international des poids et mesures) formally adopted "degree Celsius" in 1948,[15][a] formally keeping the recognized degree symbol, rather than adopting the gradian/centesimal degree symbol. For scientific use, "Celsius" is the term usually used, with "centigrade" otherwise continuing to be in common but decreasing use, especially in informal contexts in English-speaking countries.[16] It was not until February 1985 that the forecasts issued by the BBC switched from "centigrade" to "Celsius".[17] Common temperatures[edit] Some key temperatures relating the Celsius
Celsius
scale to other temperature scales are shown in the table below.

Key scale relations

Kelvin Celsius Fahrenheit

Absolute zero (precisely, by definition) 0 K −273.15 °C −459.67 °F

Boiling point
Boiling point
of liquid nitrogen 77.4 K −195.8 °C[18] −320.4 °F

Sublimation point of dry ice. 195.1 K −78 °C −108.4 °F

Intersection of Celsius
Celsius
and Fahrenheit
Fahrenheit
scales. 233.15 K −40 °C −40 °F

Melting point of H2O (purified ice)[19] 273.1499 K −0.0001 °C 31.9998 °F

Water's triple point (precisely, by definition) 273.16 K 0.01 °C 32.018 °F

Normal human body temperature
Normal human body temperature
(approximate average)[20] 310.15 K 37.0 °C 98.6 °F

Water's boiling point at 1 atm (101.325 kPa) (approximate: see Boiling point)[b] 373.1339 K 99.9839 °C 211.971 °F

Name and symbol typesetting[edit] The "degree Celsius" has been the only SI unit whose full unit name contains an uppercase letter since the SI base unit
SI base unit
for temperature, the kelvin, became the proper name in 1967 replacing the term degrees Kelvin. The plural form is degrees Celsius.[21] The general rule of the International 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").[22] Thus the value of the quantity is the product of the number and the unit, the space being regarded as a multiplication sign (just as a space between units implies multiplication). The only exceptions to this rule are for the unit symbols for degree, minute, and second for plane angle (°, ′, and ″, respectively), for which no space is left between the numerical value and the unit symbol.[23] Other languages, and various publishing houses, may follow different typographical rules. Unicode
Unicode
character[edit] Unicode
Unicode
provides the Celsius
Celsius
symbol at codepoint U+2103 ℃ degree celsius. However, this is a compatibility character provided for roundtrip compatibility with legacy encodings. It easily allows correct rendering for vertically written East Asian scripts, such as Chinese. The Unicode
Unicode
standard explicitly discourages the use of this character: "In normal use, it is better to represent degrees Celsius "°C" with a sequence of U+00B0 ° degree sign + U+0043 C latin capital letter c, rather than U+2103 ℃ degree celsius. For searching, treat these two sequences as identical."[24] Shown below is the degree Celsius
Celsius
character followed immediately by the two-component version:

℃ °C

When viewed on computers that properly support Unicode, the above line may be similar to the image in the line below (enlarged for clarity):

The canonical decomposition is simply an ordinary degree sign and "C", so some browsers may simply display "°C" in its place due to Unicode normalization. Temperatures and intervals[edit] The degree Celsius
Celsius
is a special name for the kelvin for use in expressing Celsius
Celsius
temperatures.[25] The degree Celsius
Celsius
is also 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. " Gallium
Gallium
melts at 29.7646 °C" and "The temperature outside is 23 degrees Celsius"), the degree Celsius
Celsius
is also suitable for expressing temperature intervals: 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").[26] 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
Celsius
degrees") for a temperature interval, although this usage is non-standard.[27] What is often confusing about the Celsius
Celsius
measurement is that it follows an interval system but not a ratio system; that it follows a relative scale not an absolute scale. This is put simply by illustrating that while 10 °C and 20 °C have the same interval difference as 20 °C and 30 °C, the temperature 20 °C is not twice the air heat energy as 10 °C. As this example shows, degrees Celsius
Celsius
is a useful interval measurement but does not possess the characteristics of ratio measures like weight or distance.[28] Coexistence of Kelvin
Kelvin
and Celsius
Celsius
scales[edit] In science and in engineering, the Celsius
Celsius
scale and the Kelvin
Kelvin
scale 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
Celsius
is equal to that of the kelvin, but referring to a "microdegree Celsius" would be awkward. Notwithstanding the official endorsement provided by decision #3 of Resolution 3 of the 13th CGPM, 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 of SI-prefixed forms of the degree Celsius (such as "µ°C" or "microdegrees Celsius") to express a temperature interval has not been well-adopted. Melting and boiling points of water[edit] One effect of defining the Celsius
Celsius
scale at the triple point of Vienna Standard Mean Ocean Water (VSMOW, 273.16 K and 0.01 °C), and at absolute zero (0 K and −273.15 °C), is that neither the melting nor boiling point of water under one standard atmosphere (101.325 kPa) remains a defining point for the Celsius scale. 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.[29] However, current measurements show that the difference between the triple and melting points of VSMOW
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 the absolute 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 of precisely 373.15/273.15 (approximately 36.61% thermodynamically hotter). When adhering strictly to the two-point definition for calibration, the boiling point of VSMOW
VSMOW
under one standard atmosphere of pressure is actually 373.1339 K (99.9839 °C). When calibrated to ITS-90 (a calibration standard comprising many definition points and commonly used for high-precision instrumentation), the boiling point of VSMOW is slightly less, about 99.974 °C.[30] This boiling-point difference of 16.1 millikelvin between the Celsius scale's original definition and the current 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 in barometric pressure. For example, an altitude change of only 28 cm (11 in) causes the boiling point to change by one millikelvin.

Celsius
Celsius
temperature conversion formulae

from Celsius to Celsius

Fahrenheit [°F] = [°C] × ​9⁄5 + 32 [°C] = ([°F] − 32) × ​5⁄9

Kelvin [K] = [°C] + 273.15 [°C] = [K] − 273.15

Rankine [°R] = ([°C] + 273.15) × ​9⁄5 [°C] = ([°R] − 491.67) × ​5⁄9

For temperature intervals rather than specific temperatures, 1 °C = 1 K = ​9⁄5 °F = ​9⁄5 °R Comparisons among various temperature scales

See also[edit]

Comparison of temperature scales Degrees of frost ITS-90 Réaumur scale Thermodynamic temperature

Notes[edit]

^ According to The Oxford English Dictionary (OED), the term "Celsius' thermometer" had been used at least as early as 1797. Further, the term "The Celsius
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 of Dr. Terry Quinn CBE FRS, Director of the BIPM
BIPM
(1988–2004), including " Temperature
Temperature
Scales from the early days of thermometry to the 21st century" (PDF).  (146 KiB) as well as Temperature
Temperature
(2nd Edition/1990/Academic Press/0125696817), the term Celsius
Celsius
in 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
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 word Celsius
Celsius
(but did have listings for both centigrade and centesimal in the context of temperature measurement). The 1948 adoption of Celsius
Celsius
accomplished 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
Celsius
scale its modern form, Celsius' 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 name centigrade could continue to be used 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.

^ For Vienna Standard Mean Ocean Water
Vienna Standard Mean Ocean Water
at one standard atmosphere (101.325 kPa) when calibrated solely per the two-point definition of thermodynamic temperature. Older definitions of the Celsius
Celsius
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, see VSMOW
VSMOW
in temperature measurement. There is a different approximation using ITS-90 which approximates the temperature to 99.974 °C ^ In 1948, Resolution 7 of the 9th CGPM stated, "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 by Resolution 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 kelvin 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).  (1.39 MiB).

References[edit]

^ " Celsius
Celsius
temperature scale". Encyclopædia Britannica. Retrieved 19 February 2012. Celsius
Celsius
temperature scale, also called centigrade temperature scale, scale based on 0° for the freezing point of water and 100° for the boiling point of water at 1 atm pressure.  ^ Helmenstine, Anne Marie (December 15, 2014). "What Is the Difference Between Celsius
Celsius
and Centigrade?". Chemistry.about.com. About.com. Retrieved March 16, 2015.  ^ "SI brochure, section 2.1.1.5". International Bureau of Weights and Measures. Archived from the original on 26 September 2007. Retrieved 9 May 2008.  ^ "Essentials of the SI: Base & derived units". Retrieved 9 May 2008.  ^ 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 and Fig. 1. ^ "Resolution 4 of the 10th meeting of the CGPM (1954)".  ^ Don Rittner; Ronald A. Bailey (2005): Encyclopedia of Chemistry. Facts On File, Manhattan, New York City. pp. 43. ^ Smith, Jacqueline (2009). "Appendix I: Chronology". The Facts on File
File
Dictionary of Weather and Climate. Infobase Publishing. p. 246. ISBN 978-1-4381-0951-0. 1743 Jean-Pierre Christin inverts the fixed points on Celsius' scale, to produce the scale used today.  ^ Mercure de France
Mercure de France
(1743): MEMOIRE sur la dilatation du Mercure dans le Thermométre. Chaubert; Jean de Nully, Pissot, Duchesne, Paris. pp. 1609–1610. ^ Journal helvétique (1743): LION. Imprimerie des Journalistes, Neuchâtel. pp. 308–310. ^ Memoires pour L'Histoire des Sciences et des Beaux Arts (1743): DE LYON. Chaubert, París. pp. 2125–2128. ^ Citation: Uppsala University (Sweden), Linnaeus' thermometer ^ Citation for Daniel Ekström, Mårten Strömer, Christin of Lyons: The Physics Hypertextbook, Temperature; citation for Christin of Lyons: Le Moyne College, Glossary, ( Celsius
Celsius
scale); citation for Linnaeus' connection with Pehr Elvius and Daniel Ekström: Uppsala University (Sweden), Linnaeus' thermometer; general citation: The Uppsala Astronomical Observatory, History of the Celsius
Celsius
temperature scale ^ Citations: University of Wisconsin–Madison, Linnæus & his Garden and; Uppsala University, Linnaeus' thermometer ^ "CIPM, 1948 and 9th CGPM, 1948". International Bureau of Weights and Measures. Retrieved 9 May 2008.  ^ "centigrade, adj. and n". Oxford English Dictionary. Oxford University Press. Retrieved 20 November 2011.  ^ 1985 BBC Special: A Change In The Weather on YouTube ^ Lide, D.R., ed. (1990–1991). Handbook of Chemistry and Physics. 71st ed. CRC Press. p. 4–22. ^ The ice point of purified water has been measured to be 6995890000000000000♠0.000089(10) degrees Celsius
Celsius
– see Magnum, B.W. (June 1995). "Reproducibility of the Temperature
Temperature
of the Ice Point in Routine Measurements" (PDF). Nist Technical Note. 1411. Archived from the original (PDF) on July 14, 2007. Retrieved 11 February 2007.  ^ Elert, Glenn (2005). " Temperature
Temperature
of a Healthy Human (Body Temperature)". The Physics Factbook. Retrieved 22 August 2007.  ^ "Unit of thermodynamic temperature (kelvin)". The NIST
NIST
Reference on Constants, Units, and Uncertainty: Historical context of the SI. National Institute of Standards and Technology
National Institute of Standards and Technology
(NIST). 2000. Retrieved 16 November 2011.  ^ BIPM, SI Brochure, Section 5.3.3. ^ For more information on conventions used in technical writing, see the informative SI Unit rules and style conventions by the NIST
NIST
as well as the BIPM's SI brochure: Subsection 5.3.3, Formatting the value of a quantity. ^ "22.2". The Unicode
Unicode
Standard, Version 9.0 (PDF). Mountain View, CA, USA: The Unicode
Unicode
Consortium. July 2016. ISBN 978-1-936213-13-9. Retrieved 20 April 2017.  ^ Note (e) of SI Brochure, Section, 2.2.2, Table 3 ^ Decision #3 of Resolution 3 of the 13th CGPM ^ H.D. Young, R.A. Freedman (2008). University Physics with Modern Physics (12th ed.). Addison Wesley. p. 573 ^ This fact is demonstrated in the book Biostatistics: A Guide to Design, Analysis, and Discovery By Ronald N. Forthofer, Eun Sul Lee and Mike Hernandez ^ "Resolution 3 of the 9th CGPM (1948)". International Bureau of Weights and Measures. Retrieved 9 May 2008.  ^ Citation: London South Bank University, Water Structure and Behavior, notes c1 and c2

External links[edit]

Look up Celsius
Celsius
in Wiktionary, the free dictionary.

NIST, Basic unit definitions: Kelvin The Uppsala Astronomical Observatory, History of the Celsius temperature scale London South Bank University, Water, scientific data BIPM, SI brochure, section 2.1.1.5, Unit of thermodynamic temperature TAMPILE, Comparison of temperature scales C to F converter, Celsius
Celsius
to Fahrenheit
Fahrenheit
Converter

v t e

Scales of temperature

Celsius Delisle Fahrenheit Gas Mark Kelvin Leiden Newton Planck Rankine Réaumur Rømer Wedgwood

Conversion formulas and comparison

v t e

SI units

Authority: International System of Units
International System of Units
(BIPM)

Base units

ampere candela kelvin kilogram metre mole second

Derived units with special names

becquerel coulomb degree Celsius farad gray henry hertz joule katal lumen lux newton ohm pascal radian siemens sievert steradian tesla volt watt weber

Other accepted units

astronomical unit bar dalton day decibel degree of arc electronvolt hectare hour litre minute minute of arc neper second of arc tonne atomic units natural units

See also

Conversion of units Metric prefixes Proposed redefinitions Systems of measurement

Book Category

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