#152 What is the difference between Celsius, Centigrade, Fahrenheit, and Kelvin?

I learned this today. Fahrenheit was invented first. Celsius came next. Celsius and centigrade are the same thing. Kelvin came last.

The Fahrenheit scale was invented in 1724 by the physicist Daniel Gabriel Fahrenheit. He was German by birth, but spent nearly all of his adult life in the Dutch Republic.

He set his scale, the Fahrenheit scale, based on the freezing point of water in a solution of salt water. He set this as 0℉. He used this solution because it was more commonly used in science laboratories at the time than simple water. He set the top limit at the average temperature of the human body. He used his wife and set it at 96℉. The scale was extended later on and set with 32℉ being the freezing point of water and 212℉ being the boiling point. One of the reasons his scale took off and is still used in many countries is because he invented the mercury glass thermometer. Countries that use Fahrenheit are slowly shifting to Celsius because it is a more simple system, but some countries are holding out.

Celsius and centigrade are two words for the same thing. They are both written as ℃. Celsius was invented in 1742 by the Swedish physicist Anders Celsius. He didn’t actually name it after himself, but called it centigrade because centum is Latin for 100 and gradus means steps. It was changed to Celsius in 1948 in honor of Anders Celsius.

He used the scale to define the temperatures between the freezing point of water and the boiling point of water. When he made the scale, he used 0℃ as the boiling point of water and 100℃ as the freezing point. Jean-Pierre Christin, a French physicist inverted the scale and made it what we know today. The scale is very useful for visualizing temperatures.

William Thomson, 1^st Baron Kelvin, invented the Kelvin scale in 1848. His scale uses molecular energy to differentiate between hot and cold. Kelvin is written as K and not °K. 56 Kelvin, not 56 degrees Kelvin.

The Kelvin scale is the International System of measurement for thermodynamic temperature. It starts at absolute zero, which is 0 K. Absolute zero is -273.15℃. The Kelvin scale is not generally used in conversation. It is used primarily in the scientific field.

Lord Kelvin wanted to make a system that wasn’t based on one particular gas or liquid on Earth. He wanted to make a universal system that would be the same anywhere in the universe. Water freezes at 0℃ and boils at 100℃ here on Earth, but on Mars, for example, water boils at

-4.96℃. That is because Mars only has 1% of the atmospheric pressure here on Earth. A system, such as Celsius, which is tied to the boiling and freezing points of water here on Earth, would not be relevant outside of Earth, went Lord Kelvin’s thinking.

He based his system on thermodynamic temperature. That basically means how much energy the object has. At the lowest point on his scale, absolute zero, 0 Kelvin, particles have no motion because they have no energy. The particles still move slightly because of zero-point energy, but they don’t have any transferrable kinetic energy. As an object warms up, its particles start to move more, it attains more thermodynamic energy, and it starts to move up the Kelvin scale. Water on Earth freezes at 273.2 K and it boils at 373.2 K. The sun is 5,778 K on its surface and 15 million Kelvin at its center. A supernova can reach 6 billion Kelvin. There is no upper limit to the Kelvin scale because there is no upper limit to how hot something can get. Heat is simply energy and there is no limit to how much energy something can have. The only limit is how much energy is in the entire universe and that isn’t really a limit because there would be no way to put all of the energy in the universe into one thing.

So, Fahrenheit was the first of these three systems to be invented and was used to measure the freezing temperature of a saltwater solution. Centigrade was invented to measure the temperature of freezing and boiling water and it was later renamed as Celsius. It is far easier to understand than Fahrenheit, which is why it is used in nearly every country except America. And Kelvin was a system invented to measure how much thermodynamic energy something has. And this is what I learned today.

Photo by Polina Tankilevitch from Pexels

Sources:

https://en.wikipedia.org/wiki/Thermodynamics

https://en.wikipedia.org/wiki/Kelvin

https://en.wikipedia.org/wiki/Celsius

https://www.livescience.com/temperature.html