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.
Rankine (°R)
The Rankine scale, symbol °R, was developed in 1859 by the Scottish engineer William John Macquorn Rankine. Consistently, like Kelvin, it starts at absolute zero but uses Fahrenheit-sized degrees instead of Celsius. This makes Rankine particularly useful in engineering fields within the United States, especially in thermodynamics, aerospace, and combustion studies. One Rankine equals 1°F increment, with 0°R corresponding to absolute zero. Although less common in everyday life, the Rankine scale remains important in theoretical and applied engineering, where calculations are based on the Fahrenheit system.