Celsius (°C)
The Celsius scale, indicated by °C, was devised in 1742 by Swedish astronomer Anders Celsius. His original version set 0° at water’s boiling point and 100° at its freezing point, but this arrangement was later inverted to match present-day conventions. Modern definitions relate Celsius directly to the Kelvin scale, with 0°C corresponding to 273.15 K. Today, Celsius is the most commonly used temperature scale around the world, featuring in weather reports, cooking, healthcare, and industry. Its straightforward connection to the freezing and boiling points of water makes it especially user-friendly and accessible.
Kelvin (K)
The Kelvin (K) is the SI base unit for temperature, named after the Scottish physicist William Thomson, known as Lord Kelvin, who introduced this scale in the 19th century. The scale begins at absolute zero, the point at which particles possess minimal thermal energy. Unlike Celsius or Fahrenheit, the Kelvin scale starts at an absolute reference, eliminating negative values and making it particularly useful in scientific research and engineering. Since 2019, the Kelvin has been officially tied to the Boltzmann constant, ensuring a measurement standard based on fundamental physical properties. It is extensively used in disciplines such as physics, chemistry, astronomy, and cryogenics where exact temperature readings are necessary.