Celsius (unit)

The degree Celsuis (symbol: °C) is a unit of temperature approved for use with the SI. The degree Celsius is equal to exactly one kelvin, which is defined as 1/273.16 of the thermodynamic temperature of the triple point of water. The Celsius or centigrade scale is related to the kelvin (absolute) scale by setting the temperature zero degrees Celsius (0°C) to be exactly 273.15 K, thus absolute zero is -273.15°C.

The original centigrade scale was developed by Carolus Linnaeus in 1744 and set the temperature of the melting point of water (at atmospheric pressure) to 0°C, and the boiling point of water (at atmospheric pressure) to 100°C. Due to the redefinition of the degree Celsius and the definition of "standard atmospheric pressure", the boiling point of water at one atmosphere of pressure is not exactly 100°C, but is estimated as 99.9839 °C

The Celsius scale is named for Anders Celsius (1701 – 1744), a Swedish astronomer, who developed a temperature scale similar to Linnaeus' scale in 1742, but with zero at the boiling point of water, and 100 degrees at the melting point.