Celsius

Celsius. The Celsius scale is a temperature scale used worldwide for most scientific work and daily weather reporting, defined by two fixed points: 0 degrees for the freezing point of water and 100 degrees for the boiling point of water at standard atmospheric pressure. It is one of the seven base units in the International System of Units, with the kelvin being the SI base unit for thermodynamic temperature. Named after the Swedish astronomer Anders Celsius, it is the most commonly used temperature scale globally, though the United States and a few other nations still primarily use the Fahrenheit scale.

Definition and scale

The scale is defined by assigning 0 °C to the freezing point and 100 °C to the boiling point of water under a pressure of one standard atmosphere, as defined by the International Committee for Weights and Measures. The size of one degree Celsius is exactly equal to one kelvin, the SI base unit, making the scales offset by exactly 273.15; a temperature difference of one degree Celsius is therefore identical to a difference of one kelvin. The triple point of Vienna Standard Mean Ocean Water is now used for high-precision calibration at 0.01 °C. This definition ensures worldwide consistency for scientific measurements, from laboratory experiments to global climate data collected by institutions like NASA and the World Meteorological Organization.

History

The scale was invented in 1742 by the Uppsala University professor Anders Celsius, who initially proposed a scale where 0 represented the boiling point and 100 the freezing point of water. Shortly after his death, fellow scientists including Carl Linnaeus and Mårten Strömer reversed the scale to its modern form. The scale was often called the centigrade scale until 1948, when an international conference officially renamed it in honor of Celsius. Its adoption accelerated with the metrication movements of the 19th and 20th centuries, becoming the standard for scientific work following the establishment of the General Conference on Weights and Measures. Key historical figures in thermodynamics, such as Lord Kelvin and William Thomson, later established its fundamental relationship to the absolute zero concept.

Conversion formulae

Conversions to and from other major temperature scales are performed using linear equations. To convert to the Fahrenheit scale, multiply by 9/5 and add 32 (e.g., 20 °C equals 68 °F). For conversion to the kelvin scale, simply add 273.15, as the magnitude of one degree is identical. The Rankine scale conversion requires adding 459.67 after the Fahrenheit calculation. These formulae are essential in fields like engineering, aviation, and materials science, where data from United States sources using Fahrenheit must be integrated into international projects. Precise conversions are critical in contexts such as spacecraft thermal control managed by ESA or pharmaceutical storage regulated by the World Health Organization.

Usage

It is the official temperature scale for everyday and scientific use in virtually every country, including all signatories to the Metre Convention, with notable exceptions like the United States and Belize. In science, it is used alongside the kelvin for reporting temperature intervals and Celsius temperatures, particularly in chemistry, biology, and climatology. Weather forecasts from BBC Weather to the Japan Meteorological Agency report in degrees Celsius. The scale is mandated in technical standards from organizations like ISO and is used in manufacturing from Siemens factories to Toyota assembly lines. Medical professionals worldwide, following guidelines from the American Medical Association, use it for reporting body temperature and storing vaccines.

Related temperature scales

Several other temperature scales have historical or specialized relationships. The kelvin is its direct thermodynamic counterpart, sharing the same unit magnitude but starting at absolute zero. The Fahrenheit scale, used primarily in the United States, defines water's freezing and boiling points as 32 °F and 212 °F. The Rankine scale is the Fahrenheit equivalent of the kelvin scale, used in some aerospace engineering in the United States. Obsolete scales like the Réaumur scale, once popular in parts of Europe, and the Delisle scale, used in 18th-century Russia, defined different fixed points. The Newton scale and Rømer scale were other early competitors before the widespread adoption of the metric system championed by nations like France and Germany. Category:Units of temperature Category:Metric system