One of the weather apps on my phone showed this Monday morning.

When the phone knows where our house is, it chooses the nearest community, which is called Coosa.

The weather app usually has an hourly temperature for 24 hours. This time it showed an hourly temperature for 48 hours. Everything looked OK for the first 24 hours, and then it showed -459 degrees for the next 24 hours. Before I say anything about it, I would like you, faithful reader, to see if you can guess what that might mean. What is the significance of -459 degrees? Note that the other temperatures are Fahrenheit.

Here’s what I think.

First, there are at least four temperature scales in common use, depending on your definition of common. The one most often used in the US is the Fahrenheit scale. The one used in almost the entire rest of the world is the Celsius scale. According to Wikipedia, “Fahrenheit is used in the Bahamas, Belize, the Cayman Islands, Palau, and the United States and associated territories of American Samoa and the U.S. Virgin Islands for everyday applications.” As almost everyone knows, 32 is the freezing point of water in Fahrenheit, and zero is the freezing point in Celsius. There are nine Fahrenheit degrees for every five Celsius degrees.

The third commonly-used scale is Kelvin, which uses the same degrees as Celsius but sets zero at absolute zero, which is usually taken to be the lowest possible temperature that a material can reach. Zero Kelvin is -273.15 C.

Absolute zero in the Fahrenheit scale is -459.67. So apparently someone expected the temperatures for the following day to be absolute zero.

Of course that’s not true. My guess as to what happened is that the programming that creates the weather app expects an input for temperatures in Kelvin, and then converts the input values into Fahrenheit. Since the app does not usually show temperatures for beyond 24 hours, those values were probably zero. The program sees those zeroes as Kelvin, and 0 Kelvin is (approximately) -459 F. So that’s my guess as to why those values showed up.

I mentioned four “commonly” used temperature scales. The fourth is Rankine, which uses Fahrenheit degrees but sets zero at absolute zero, the same as Kelvin. The only place I have ever seen Rankine used is in a huge, complex program I ran when I worked in Huntsville. The program was intended to calculate heating and optical signatures of objects flying in space, like, typically, reentry vehicles (the explosive tip of a ballistic missile). Many parts of it were written more than 40 years ago, and much of it was written by engineers. Engineers, in my experience , tend to use what they have always used, and most engineers in those days used American units. So much of the program was written using the American system of weights and measures, sometimes called English units, or customary units.

Most people in the civilized world, especially scientists, use the International System of weights and measures, usually called the metric system. Even American scientists use it. It’s usually designated as “SI”, using the French word order.

I fairly intensely dislike the American system, although I use it daily for speeds, weights and temperatures (you know, when in Rome …). I fumed every time I had to convert SI units into American units for the program I used. Later updates allowed SI units as input, although I think the program still did its calculations in American units.

Later on Monday the second 24 hours disappeared and so did the -459 degree temperatures.