Is Celsius an si unit?


Celsius (known until 1948 as centigrade) is a temperature scale that is named after the Swedish astronomer Anders Celsius (1701-1744), who developed a similar temperature scale two years before his death. It is a Celsius unit.

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Anders Celsius

Anders Celsius (27 November 1701 – 25 April 1744) was a Swedish astronomer, physicist and mathematician. 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 bears his surname, though this was revised in 1745 by Carl Linnaeus, inverting the original scale, one year after Celsius' death from tuberculosis.

Anders Celsius was born in Uppsala, Sweden on 27 November 1701. His family originated from Ovanåker in the province of Hälsingland. Their family estate was at Doma, also known as Höjen or Högen (locally as Högen 2). The name Celsius is a latinization of the estate's name (Latin celsus "mound").

Physical quantities

A physical quantity (or "physical magnitude") is a physical property of a phenomenon, body, or substance, that can be quantified by measurement.

Celsius Temperature
Scale of temperature

Scale of temperature is a way to measure temperature quantitatively.

According to the zeroth law of thermodynamics, being in thermal equilibrium is an equivalence relation. Thus all thermal systems may be divided into a quotient set by this equivalence relation, denoted below as M. Assume the set M has the cardinality of c, then one can construct an injective function ƒ: M → R , by which every thermal system will have a number associated with it such that when and only when two thermal systems have same such value, they will be in thermal equilibrium. This is clearly the property of temperature, and the specific way of assigning numerical values as temperature is called a scale of temperature. In practical terms, a temperature scale is always based on usually a single physical property of a simple thermodynamic system, called a thermometer, that defines a scaling function mapping the temperature to the measurable thermometric parameter. Such temperature scales that are purely based on measurement are called empirical temperature scales.

Olof Celsius

Olof Celsius (the elder) (July 19, 1670 – June 24, 1756) was a Swedish botanist, philologist and clergyman, He was a professor at Uppsala University, Sweden. Celsius was a mentor of the botanist and scientist Carolus Linnaeus. Celsius wrote his most famous book on biblical plants, Hierobotanicos, in 1745-47.

Olof Celsius's nephew Anders Celsius was an astronomer who invented a temperature scale where 100 represented the freezing point and 0 the boiling point of water. Carl Linnaeus in 1744 reversed the scale to create the centigrade scale, renamed in 1948 to the Celsius scale in use today.

Mercury-in-glass thermometer

The mercury-in-glass or mercury thermometer was invented by physicist Daniel Gabriel Fahrenheit in Amsterdam (1714). It consists of a bulb containing mercury attached to a glass tube of narrow diameter; the volume of mercury in the tube is much less than the volume in the bulb. The volume of mercury changes slightly with temperature; the small change in volume drives the narrow mercury column a relatively long way up the tube. The space above the mercury may be filled with nitrogen or it may be at less than atmospheric pressure, a partial vacuum.

In order to calibrate the thermometer, the bulb is made to reach thermal equilibrium with a temperature standard such as an ice/water mixture, and then with another standard such as water/vapour, and the tube is divided into regular intervals between the fixed points. In principle, thermometers made of different material (e.g., coloured alcohol thermometers) might be expected to give different intermediate readings due to different expansion properties; in practice the substances used are chosen to have reasonably linear expansion characteristics as a function of true thermodynamic temperature, and so give similar results.

Measurement Thermodynamics Physics

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