Celsius facts for kids

A thermometer calibrated in degrees Celsius

The degree Celsius is the unit of temperature on the Celsius temperature scale. It is named after the Swedish astronomer Anders Celsius (1701–1744), who proposed the first version of it in 1742. The unit was called centigrade in several languages (from the Latin centum, which means 100, and gradus, which means steps) for many years. In 1948, the International Committee for Weights and Measures renamed it to honor Celsius. Most countries use this scale (the Fahrenheit scale is still used in the United States, some island territories, and Liberia).

Throughout the 19th century, the 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. (In Celsius's initial proposal, the values were reversed: the boiling point was 0 degrees and the freezing point was 100 degrees.)

Between 1954 and 2019, the precise definitions of the unit degree Celsius and the Celsius temperature scale used absolute zero and the triple point of water. Since 2007, the Celsius temperature scale has been defined in terms of the kelvin, the SI base unit of thermodynamic temperature (symbol: K). Absolute zero, the lowest temperature, is now defined as being exactly 0 K and −273.15 °C.

History

Anders Celsius's original thermometer used a reversed scale, with 100 as the freezing point and 0 as the boiling point of water.

In 1742, Swedish astronomer Anders Celsius (1701–1744) created a temperature scale that was the reverse of the scale now known as "Celsius": 0 represented the boiling point of water, while 100 represented the freezing point of water. 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) in 1954 defined one standard atmosphere to equal precisely 1,013,250 dynes per square centimeter (101.325 kPa).

In 1743, the Lyonnais physicist Jean-Pierre Christin, permanent secretary of the Academy of Lyon, inverted the Celsius temperature scale so that 0 represented the freezing point of water and 100 represented the boiling point of water. Some credit Christin for independently inventing the reverse of Celsius's original scale, while others believe Christin merely reversed Celsius's scale. On 19 May 1743 he published the design of a mercury thermometer, the "Thermometer of Lyon" built by the craftsman Pierre Casati that used this scale.

In 1744, coincident with the death of Anders Celsius, the Swedish botanist Carl Linnaeus (1707–1778) reversed Celsius's scale. 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, 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; 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 reporting temperatures in this modern "forward" Celsius temperature 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" versus "Celsius"

Since the 19th century, the scientific and thermometry communities worldwide have used the phrase "centigrade scale" and temperatures were often reported simply as "degrees" or, when greater specificity was desired, as "degrees centigrade", with the symbol °C.

In the French language, the term centigrade also means one hundredth of a gradian, when used for angular measurement. The term centesimal degree was later introduced for temperatures but was also problematic, as it means gradian (one hundredth of a right angle) in the French and Spanish languages. The risk of confusion between temperature and angular measurement was eliminated in 1948 when the 9th meeting of the General Conference on Weights and Measures and the Comité International des Poids et Mesures (CIPM) formally adopted "degree Celsius" for temperature.

While "Celsius" is commonly used in scientific work, "centigrade" is still used in French and English-speaking countries, especially in informal contexts. The frequency of the usage of "centigrade" has declined over time.

Due to metrication in Australia, after 1 September 1972 weather reports in the country were exclusively given in Celsius. In the United Kingdom, it was not until February 1985 that forecasts by BBC Weather switched from "centigrade" to "Celsius".

Common temperatures

Equivalent temperatures in kelvin (K), Rankine (R), Celsius (°C), and Fahrenheit (°F)

All phase transitions are at standard atmosphere. Figures are either by definition, or approximated from empirical measurements.

Temperature conversions

• To make a temperature in degrees Celsius into kelvins a person must add 273.15. For example, 0 degrees Celsius, which is the temperature at which water freezes, is 273.15 kelvins.
• To make a temperature in kelvins into degrees Celsius a person must subtract 273.15. For example, 310 K is the same temperature as 36.85 °C, which is about the temperature of a human body.
• To make a temperature in degrees Celsius into degrees Fahrenheit a person must multiply it by 9/5 and add 32: F = (9/5)C + 32.
• To make a temperature in degrees Fahrenheit into degrees Celsius a person must subtract 32 and multiply the result by 5/9: C = (F - 32) * 5/9.

Images for kids

• 

  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.

See also

In Spanish: Grado Celsius para niños