Celsius

Celsius is a temperature scale named after the Swedish astronomer Anders Celsius. It is widely used around the world for everyday temperature, science, medicine, and industry. The unit of measurement on this scale is the degree Celsius (°C); the scale is defined so that the size of one degree Celsius is the same as one kelvin.

Definition and relationship to Kelvin: 0 °C is the freezing point of water at standard atmospheric pressure, and 100 °C is the boiling point of water at the same pressure. The Celsius scale is directly related to the Kelvin scale by the equation T_C = T_K − 273.15, so the interval of one degree is the same in both scales. In the current SI system, the kelvin is the base unit of thermodynamic temperature, while the degree Celsius is a widely used derived unit for convenience in daily life and many scientific contexts. The offset between Celsius and Kelvin is exact: 0 °C equals 273.15 K.

History: The scale is named for Anders Celsius (1701–1744). In 1742 he proposed a scale that initially had 0 at the boiling point and 100 at the freezing point of water; after his death, the scale was inverted to its modern form, so that 0 °C represents the freezing point and 100 °C the boiling point at standard pressure.

Usage and regional variation: The Celsius scale is the predominant temperature scale in most countries for weather, cooking, medicine, and engineering. In the United States, Fahrenheit is commonly used for everyday air temperatures, while Celsius is standard in science, many industries, and international contexts.