Celsius scale

Celsius scale
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Name	Celsius scale
Unit	degree Celsius (°C)
Quantity	Temperature
Based on	Zero point at water's triple point (2019 definition via kelvin)
Derived from	Kelvin

Celsius scale is a temperature scale widely used for everyday, scientific, and industrial temperature measurement. It aligns with the thermodynamic kelvin through an affixed offset and is integral to international systems of measurement employed by organizations such as the International System of Units and agencies like the International Bureau of Weights and Measures. Originating in early 18th-century Scandinavia and refined across European scientific institutions, the scale underpins meteorology, thermodynamics, and modern standards in laboratories and industry.

History

The origin of the scale traces to Swedish astronomer Anders Celsius and contemporaries including Daniel Gabriel Fahrenheit and René Antoine Ferchault de Réaumur. Early temperature proposals appeared in the milieu of the Age of Enlightenment alongside work by members of the Royal Society and the Académie des Sciences. The scale evolved through debates in scientific societies such as the Royal Institution, and refinements were influenced by instrument makers in Stockholm, Berlin, and Paris. Transition from empirical fixed points—like melting ice used by Antoine Lavoisier adherents—to reproducible standards was driven by developments at institutions including the National Physical Laboratory (United Kingdom) and the Physikalisch-Technische Bundesanstalt.

Definition and units

The unit of the scale is the degree Celsius (°C). Since the 2019 redefinition of the SI base unit for temperature, the Celsius scale is defined by assigning the value of the thermodynamic kelvin in relation to the triple point of water and the Boltzmann constant established by consensus at meetings of the General Conference on Weights and Measures. One degree Celsius equals one kelvin in magnitude; the zero point is offset relative to kelvin by 273.15 units. Practical international standards are maintained by the International Committee for Weights and Measures and disseminated through reference laboratories such as the National Institute of Standards and Technology and the Bureau International des Poids et Mesures.

Measurement and instrumentation

Measurements on the scale are obtained using thermometers and sensors traceable to national metrology institutes like NIST and PTB (Germany). Common instruments include mercury-in-glass thermometers historically manufactured by companies in London and Gothenburg, platinum resistance thermometers developed by researchers associated with the University of Cambridge and the Max Planck Society, thermocouples employed in engineering contexts tied to Siemens technologies, and modern thermistors used by firms such as Honeywell and Texas Instruments. Calibration protocols reference fixed points such as the triple point of water and the melting points of metals documented by the American Physical Society and the International Union of Pure and Applied Physics. Quality assurance and accreditation follow criteria set by ISO standards and national accreditation bodies like the United Kingdom Accreditation Service.

Relation to other temperature scales

The Celsius scale is linearly related to kelvin, Fahrenheit, and Rankine scales. Conversion formulas are standardized in guidance from the International Organization for Standardization and used by agencies such as NASA and the European Space Agency for instrumentation interoperability. Historical alternatives such as the Réaumur scale and practices in regions influenced by scientists like Gabriel Fahrenheit persisted until harmonization efforts at the Metre Convention and subsequent international congresses. Scientific reporting in journals published by the American Chemical Society and the Royal Society of Chemistry typically requires SI-aligned Celsius or kelvin notation with explicit conversion where necessary.

Applications and usage

The scale is used in meteorology by services like the UK Met Office and Météo-France, in medicine by institutions such as the World Health Organization and hospitals affiliated with the Mayo Clinic, and in engineering projects executed by firms such as General Electric and Siemens. In food safety, standards set by organizations like the Food and Agriculture Organization and national agencies require Celsius temperature ranges for storage and processing. Laboratories in universities including Harvard University and the University of Tokyo report experimental temperatures in Celsius or kelvin per editorial policies of publishers like Nature Publishing Group and Springer Nature.

Accuracy, calibration, and standards

Ensuring accuracy involves traceability to primary standards at national metrology institutes such as NIST, PTB (Germany), and the Laboratoire national de métrologie et d'essais. Calibration utilizes reference cells for the triple point of water maintained under protocols recommended by the International Bureau of Weights and Measures and compliance frameworks like ISO/IEC 17025. Uncertainty budgets are compiled following guidelines from the Joint Committee for Guides in Metrology and reported in conformity with statistical practices endorsed by organizations including the Institute of Electrical and Electronics Engineers and the International Organization for Standardization. Legal measurement requirements are overseen in many countries by agencies such as the National Institute of Metrology, China and the Federal Institute of Metrology (METAS).

Category:Temperature scales