Seriously… not again… it’s another ongoing war. I hope you’re aware that there are two commonly used temperature scales, Celsius and Fahrenheit, even though you’ll probably only ever use one of them. But perhaps there are other scales that dare step up and take the challenge?
In 1724 German physicist Daniel Gabriel Fahrenheit proposed his namesake scale by setting three points. The first point, 0 °F, was defined to be the stabilised temperature of brine (a mixture of ice, water and ammonium chloride in a 1:1:1 ratio). The second point, 32 °F, was the temperature of ice and water in a 1:1 ratio (essentially the temperature at which water freezes). The third point, 96 °F, was approximately core human body temperature (originally called blood heat).
Later, for extra scientific precision, the scale was redefined so that the freezing point of water was exactly 32 °F and the boiling point of water was exactly 212 °F, both measured at standard atmospheric pressure (1 atm or 101325 Pa). This is important because at lower atmospheric pressures, such as those at higher altitudes, water boils at a much lower temperature, and vice versa.
In 1742 Swedish astronomer Anders Celsius proposed his namesake scale by setting two points, which was the reverse of the scale that we use today. 0 °C was defined to be the boiling point of water and 100 °C was defined to be the freezing point of water, once again calibrated at 1 atm, so you would become more negative as you rose in temperature. It was only in 1744 when Swedish botanist Carolus Linnaeus reversed the scale.
Where does the word ‘centigrade’ originate from? ‘Centum’ is Latin for a hundred (as there are 100 degrees between the melting and boiling points of water), and ‘gradus’ is steps. The scale was then renamed in honour of Celsius in 1948.
As of now, the USA, some Pacific islands and a few other countries around Central America are the only countries to officially use the Fahrenheit scale, whereas every other country uses degrees Celsius.
You may have also heard of the term ‘Kelvin’. The Kelvin scale is named after Irish and Scottish physicist William Thomson (later to be known as Lord Kelvin). The Kelvin scale is surprisingly the SI unit of temperature due to its one very important property – it is a thermodynamic scale. Thermodynamic scales reach zero at absolute zero, the coldest possible temperature at which matter has minimal energy. And because the Kelvin is an SI unit, it is always used over other scales in any scientific calculations.
An increment of 1 K is the same as an increment of 1 °C, and the Kelvin is defined such that the triple point of water is 273.16 K (0.01 °C), and as a result absolute zero is -273.15 K. Therefore the Kelvin scale is essentially offset from the Celsius scale by 273.15 units.
Another, more obscure scale is the Rankine scale, developed by Scottish engineer William John Macquorn Rankine in 1859. The Rankine is to Fahrenheit as Kelvin is to Celsius, i.e. the Rankine scale is the Fahrenheit scale offset so that 0 °R is absolute zero.
Other minor scales include the Rømer scale which defines the freezing point of water to be 7.5 °Rø and the boiling point to be 60 °Rø, and also the Newton, Delisle and Réaumur scales.
I’ll leave this image with you (so that you may stifle a groan):
Thus you can be cooled down to -273.15 ℃ and still be 0K (I will see myself out now).