In the late 1960s and 1970s, the Celsius (formerly Centigrade) scale was phased in by governments as part of the standardizing process of metrication.įahrenheit supporters assert its previous popularity was due to Fahrenheit’s user-friendliness. The Fahrenheit scale was the primary temperature standard for climatic, industrial and medical purposes in most English-speaking countries until the 1960s. The United Kingdom has almost exclusively used the Celsius scale since the 1970s, with the notable exception that some broadcasters and publications still quote Fahrenheit air temperatures occasionally in weather forecasts, for the benefit of generations born before about 1950, and air-temperature thermometers sold still show both scales for the same reason. Fahrenheit is sometimes used by older generations in English speaking countries, especially for measurement of higher temperatures. All other countries have adopted Celsius as the primary scale in use. In the United States the Fahrenheit system continues to be the accepted standard for non-scientific use. The boiling point of water is 100 Celsius or 212 degrees Fahrenheit. The freezing point of water is 0 Celsius or 32 degrees Fahrenheit. This picture compares Celsius and Fahrenheit scales on a thermometer.Ĭelsius and Fahrenheit thermometers side by side compare the two scales. The Fahrenheit scale coincides with the Celsius scale at -40 ☏, which is the same temperature as -40 ☌. On the Celsius scale, the freezing and boiling points of water are exactly 100 degrees apart, thus the unit of the Fahrenheit scale, a degree Fahrenheit, is 5/9 of a degree Celsius. The triple point of water is defined as being precisely 273.16 K and 0.01 ☌. Absolute zero-the temperature at which nothing could be colder and no heat energy remains in a substance-is defined as being precisely 0 K and −273.15 ☌. This definition also precisely relates the Celsius scale to the Kelvin scale, which is the SI base unit of temperature (symbol: K). However, the unit “degree Celsius” and the Celsius scale are currently, by international agreement, defined by two different points: absolute zero, and the triple point of specially prepared water. Until 1954, 0 ☌ on the Celsius scale was defined as the melting point of ice and 100 ☌ was defined as the boiling point of water under a pressure of one standard atmosphere this close equivalence is taught in schools today. “Celsius” is named after the Swedish astronomer Anders Celsius (1701-1744), who developed a similar temperature scale two years before his death. The degree Celsius (symbol: ☌) can refer to a specific temperature on the Celsius scale as well as serve as unit increment to indicate a temperature interval(a difference between two temperatures or an uncertainty). In this scale, the freezing point of water is 32 degrees Fahrenheit (written “32 ☏”), and the boiling point is 212 degrees, placing the boiling and freezing points of water exactly 180 degrees apart.Ĭelsius is, or relates to, the Celsius temperature scale (previously known as the centigrade scale). Fahrenheit is a temperature scale named after the German-Dutch physicist Daniel Gabriel Fahrenheit (1686–1736), who proposed it in 1724.
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