Celsius (known until 1948 as centigrade) is a temperature Historically, two equivalent concepts of temperature have developed, the thermodynamic description and a microscopic explanation based on statistical physics. Since thermodynamics deals entirely with macroscopic measurements, the thermodynamic definition of temperature, first stated by Lord Kelvin, is stated entirely in empirical, measurable scale that is named after the Swedish astronomer Anders Celsius Anders Celsius was a Swedish astronomer. He was professor of astronomy at Uppsala University from 1730 to 1744, but traveled from 1732 to 1735 visiting notable observatories in Germany, Italy and France. He founded the Uppsala Astronomical Observatory in 1741, and in 1742 he proposed the Celsius temperature scale which takes his name. The scale (1701–1744), who developed a similar temperature scale two years before his death. The degree Celsius (°C) can refer to a specific temperature on the Celsius scale as well as a unit to indicate a temperature interval In mathematics, a interval is a set of real numbers with the property that any number that lies between two numbers in the set is also included in the set. For example, the set of all numbers x satisfying is an interval which contains 0 and 1, as well as all numbers between them. Other examples of intervals are the set of all real numbers , the (a difference between two temperatures or an uncertainty Uncertainty is a term used in subtly different ways in a number of fields, including philosophy, physics, statistics, economics, finance, insurance, psychology, sociology, engineering, and information science. It applies to predictions of future events, to physical measurements already made, or to the unknown).
From 1744 until 1954, 0 °C was defined as the freezing point of water and 100 °C was defined as the boiling point of water, both at a pressure of one standard atmosphere The standard atmosphere is an international reference pressure defined as 101,325 Pa and formerly used as unit of pressure. For practical purposes it has been replaced by the bar which is 100,000 Pa. The difference of about 1% is not significant for many applications, and is within the error range of common pressure gauges.[citation needed] Although these defining correlations are commonly taught in schools today, by international agreement the unit "degree Celsius" and the Celsius scale are currently defined by two different points: 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 the triple point In thermodynamics, the triple point of a substance is the temperature and pressure at which three phases of that substance coexist in thermodynamic equilibrium. For example, the triple point of mercury occurs at a temperature of −38.8344 °C and a pressure of 0.2 mPa of VSMOW VSMOW, or Vienna Standard Mean Ocean Water, is an isotopic water standard defined in 1968 by the International Atomic Energy Agency. Despite the misleading phrase "ocean water", VSMOW does not include any salt or other substances usually found in seawater and refers to pure water with a particular composition of isotopes. VSMOW serves as (specially prepared water). This definition also precisely relates the Celsius scale to the Kelvin 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 scale, which defines the 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 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 thermodynamic temperature Thermodynamic temperature is the absolute measure of temperature and is one of the principal parameters of thermodynamics. Thermodynamic temperature is an "absolute" scale because it is the measure of the fundamental property underlying temperature: its null or zero point, absolute zero, is the temperature at which the particle (symbol: K). Absolute zero, the hypothetical but unattainable temperature at which matter exhibits zero entropy, is defined as being precisely 0 K and −273.15 °C. The temperature value of the triple point of water is defined as being precisely 273.16 K and 0.01 °C.[1]
This definition fixes the magnitude of both the degree Celsius and the kelvin as precisely 1 part in 273.16 parts, the difference between absolute zero and the triple point of water. Thus, it sets the magnitude of one degree Celsius and that of one kelvin as exactly the same. Additionally, it establishes the difference between the two scales' null points as being precisely 273.15 degrees Celsius (−273.15 °C = 0 K and 0 °C = 273.15 K).[2]
An illustration of Anders Celsius's original thermometer. Note the reversed scale, where 0 is the boiling point of water and 100 is its freezing point.
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History
In 1742 Swedish Sweden (pronounced /ˈswiːdən/ SWEE-dən, Swedish: Sverige pronounced [ˈsveːrijə] ( listen)), officially the Kingdom of Sweden (Swedish: Konungariket Sverige (help·info)), is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden has land borders with Norway to the west and Finland to the northeast, and water borders with astronomer Anders Celsius Anders Celsius was a Swedish astronomer. He was professor of astronomy at Uppsala University from 1730 to 1744, but traveled from 1732 to 1735 visiting notable observatories in Germany, Italy and France. He founded the Uppsala Astronomical Observatory in 1741, and in 1742 he proposed the Celsius temperature scale which takes his name. The scale (1701–1744) originally created a "reversed" version of the modern Celsius temperature scale whereby zero represented the boiling point of water and one hundred represented the freezing point of water. In his paper Observations of two persistent degrees on a thermometer, he recounted his experiments showing that ice's melting point was essentially unaffected by pressure. He also determined with remarkable precision how water's boiling point varied as a function of atmospheric pressure. He proposed that zero on his temperature scale (water's boiling point) would be calibrated at the mean barometric pressure at mean sea level. This pressure is known as one standard atmosphere The standard atmosphere is an international reference pressure defined as 101,325 Pa and formerly used as unit of pressure. For practical purposes it has been replaced by the bar which is 100,000 Pa. The difference of about 1% is not significant for many applications, and is within the error range of common pressure gauges. (The BIPM The International Bureau of Weights and Measures , is an international standards organisation, one of three such organisations established to maintain the International System of Units (SI) under the terms of the Metre Convention (Convention du Mètre). The organisation is usually referred to by its French initialism, BIPM's 10th CGPM The General Conference on Weights and Measures is the English name of the Conférence générale des poids et mesures . It is one of the three organizations established to maintain the International System of Units (SI) under the terms of the Convention du Mètre (Metre Convention) of 1875. It meets in Sèvres (in the southwestern suburbs of Paris) later defined one standard atmosphere to equal precisely 1,013,250 dynes In physics, the dyne (symbol "dyn", from Greek δύναμις meaning power, force) is a unit of force specified in the centimetre-gram-second (CGS) system of units, a predecessor of the modern SI. One dyne is equal to exactly 10 µ per square centimeter The square metre is the SI derived unit of area, with symbol m2 (33A1 in Unicode). It is defined as the area of a square whose sides measure exactly one metre. The square metre is derived from the SI base unit of the metre, which in turn is defined as the length of the path travelled by light in absolute vacuum during a time interval of 1⁄299,792 (101.325 kPa))
In 1744, coincident with the death of Anders Celsius, the Swedish botanist Carolus Linnaeus Carl Linnaeus [a 2] (Latinized as Carolus Linnaeus [a 3], also known after his ennoblement as Carl von Linné , 23 May[a 1] 1707 – 10 January 1778) was a Swedish botanist, physician, and zoologist, who laid the foundations for the modern scheme of binomial nomenclature. He is known as the father of modern taxonomy, and is also considered one of (1707–1778) effectively reversed[3] Celsius's scale upon receipt of his first thermometer featuring a scale where zero represented the melting point of ice and 100 represented water's boiling point. 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;[4] 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; Christian of Lyons; Daniel Ekström, the instrument maker; and Mårten Strömer (1707–1770) who had studied astronomy under Anders Celsius.
The first known document[5] reporting temperatures in this modern "forward" 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 Botanical Garden of Uppsala University:
"... 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 and Celsius
For the next 204 years, 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, "degrees centigrade". The symbol for temperature values on this scale was °C (in several formats over the years).
Because the term centigrade was also the Spanish and French language name for a unit of angular measurement (1/10,000 of a right angle) and had a similar connotation in other languages, the term "centesimal degree" was used when very precise, unambiguous language was required by international standards bodies such as the Bureau international des poids et mesures The International Bureau of Weights and Measures , is an international standards organisation, one of three such organisations established to maintain the International System of Units (SI) under the terms of the Metre Convention (Convention du Mètre). The organisation is usually referred to by its French initialism, BIPM (BIPM). The 9th CGPM (Conférence générale des poids et mesures The General Conference on Weights and Measures is the English name of the Conférence générale des poids et mesures . It is one of the three organizations established to maintain the International System of Units (SI) under the terms of the Convention du Mètre (Metre Convention) of 1875. It meets in Sèvres (in the southwestern suburbs of Paris)) and the CIPM (Comité international des poids et mesures The International Committee for Weights and Measures is the English name of the Comité international des poids et mesures . It consists of eighteen persons from Member States of the Metre Convention (Convention du Mètre). Its principal task is to ensure world-wide uniformity in units of measurement and it does this by direct action or by) formally adopted "degree Celsius" (symbol: °C) in 1948.[6][7] Some people still use the old term.
Common temperatures
Some key temperatures relating the Celsius scale to other temperature scales are shown in the table below.
Formatting
The "degree Celsius" has been the only SI unit whose full unit name contains an uppercase letter since its 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:, the kelvin, became the proper name in 1967 for the obsolete term, the "degree Kelvin". The correct plural form is "degrees Celsius".
The general rule is that the numerical value always precedes the unit, and a space is always used to separate the unit from the number, e.g., "23 °C" (not "23°C" or "23° C"). 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.[10]
The special Unicode degree Celsius character
Unicode Unicode is a computing industry standard for the consistent representation and handling of text expressed in most of the world's writing systems. Developed in conjunction with the Universal Character Set standard and published in book form as The Unicode Standard, the latest version of Unicode consists of a repertoire of more than 107,000 provides a compatibility character In discussing Unicode and the UCS, many often refer to compatibility characters. Compatibility characters are graphical characters that are discouraged by the Unicode Consortium. As the Unicode consortium says: for the degree Celsius at U+2103 (decimal 8451), for compatibility with CJK encodings that provide such a character (as such, in most fonts the width is the same as for fullwidth In CJK computing, graphic characters are traditionally classed into fullwidth and halfwidth (in Taiwan and Hong Kong: 半形; elsewhere: 半角) characters. With fixed-width fonts, a halfwidth character occupies half the width of a fullwidth character, hence the name characters). Its appearance is similar to the one synthesized by individually typing its two components (°) and (C). Shown below is the degree 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 Unicode contains numerous characters to maintain compatibility with existing standards, some of which are functionally equivalent to other characters or sequences of characters. Because of this, Unicode defines some code point sequences as equivalent. Unicode provides two notions of equivalence: canonical, and compatibility, the former being a is simply an ordinary degree sign and "C", so some browsers may simply display "°C" in its place due to Unicode normalization Unicode contains numerous characters to maintain compatibility with existing standards, some of which are functionally equivalent to other characters or sequences of characters. Because of this, Unicode defines some code point sequences as equivalent. Unicode provides two notions of equivalence: canonical, and compatible, the former being a subset.
Temperatures and intervals
The degree Celsius is a special name for the kelvin for use in expressing Celsius temperatures.[11] The degree 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 is a chemical element that has the symbol Ga and atomic number 31. Elemental gallium does not occur in nature, but as the gallium(III) salt in trace amounts in bauxite and zinc ores. A soft silvery metallic poor metal, elemental gallium is a brittle solid at low temperatures. As it liquefies slightly above room temperature, it will melt in melts at 29.7646 °C" and "The temperature outside is 23 degrees Celsius"), the degree 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").[12] 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.[13] What is often confused about the Celsius measurement is that it follows an interval system but not a ratio system or 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 is a useful interval measurement but does not possess the characteristics of ratio measures like weight or distance.[14]
Why technical articles use a mix of kelvin and Celsius scales
In science (especially) and in engineering, the Celsius scale and the kelvin are often used simultaneously in the same article (e.g. "…its measured value was 0.01023 °C with an uncertainty of 70 µK…"). This practice is permissible because:
- the degree Celsius is a special name for the kelvin for use in expressing Celsius temperatures, and
- the magnitude of the degree Celsius is precisely equal to that of the kelvin.
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 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 forms of the degree Celsius (such as "µ°C" or "microdegrees Celsius") to express a temperature interval has not been well-adopted.
This practice should be avoided for literature directed to lower-level technical fields and in non-technical articles intended for the general public where both the kelvin and its symbol, K, are not well recognised and could be confusing.
Sat, 04 Sep 2010 16:10:11 GMT+00:00
Times of India Rains lashed various parts of Punjab and Haryana with Chandigarh receiving 9.2 mm of rainfall and recording maximum temperature of 31.9 degree Celsius . ...
