Stellar Temperature Measurement

There are several temperature scales in use today. One degree of temperature difference is not the same in the various scales, and which temperature is called zero degrees also varies. The two most widely used temperature scales for everyday use are the Fahrenheit and Celsius scales. A temperature scale that is used a lot in science (and astronomy in particular) is the Kelvin scale. These scales are described below:

- The Celsius scale was invented by the Swedish astronomer Anders Celsius (1701-1744, Sweden). It is fixed by two temperatures: zero degrees Celsius is the freezing temperature of water (at a standard sea-level air pressure), and a hundred degrees Celsius is the boiling temperature of water at the same pressure.
- The zero point of the Celsius scale is practical, because below zero degrees Celsius you have to watch for ice on the roads and for frozen water pipes.
- Zero degrees Celsius corresponds to 32 degrees Fahrenheit and 273.15 kelvin. A hundred degrees Celsius corresponds to 212 degrees Fahrenheit and to 373.15 kelvin. To change from degrees Fahrenheit to degrees Celsius, use this link: Temperature Conversion Calculator.

__Celsius scale__

__Fahrenheit scale__

- The Fahrenheit scale was invented by the German scientist Daniel Gabriel Fahrenheit (1686 Poland - 1736 Dutch Republic). It is fixed by two temperatures: zero degrees Fahrenheit was the temperature of a mix of water, ice, and salt. Ninety degrees Fahrenheit was what people in those days thought was the normal temperature of the human body.
- These two fixed points on the Fahrenheit scale were perhaps not the most practical choices, because most people do not spend a lot of time trying to keep water fluid by adding salt to it, and we now know that the temperature that people then thought was the normal temperature of the human body was in fact a few degrees wrong.
- Zero degrees Fahrenheit corresponds to about -17.8 degrees Celsius and about 255.4 kelvin. One hundred degrees Fahrenheit corresponds to about 37.8 degrees Celsius and to about 310.9 kelvin. To change from degrees Fahrenheit to degrees Celsius, use this link: Temperature Conversion Calculator.

__Kelvin Scale__

- The Kelvin scale is named after the British scientist Lord Kelvin,
- (William
Thompson), Baron Kelvin of Largs. It is fixed by one temperature
and
a temperature difference: zero kelvin (don't say
*degree.*kelvin and don't write kelvin with a capital K) is the lowest possible temperature, at which not even atoms move around anymore. A difference of one kelvin corresponds to a difference of one degree Celsius. This scale was invented by scientists for use in physics, because some formulas (those relating pressure of a gas to its temperature, or brightness to temperature, for instance) become easier if you use the zero point of the Kelvin scale. You'll notice that the formulas for the equilibrium temperatures above are also simpler when the Kelvin scale is used. The symbol for kelvin is K, so you can write 100 kelvin also as 100 K. - The National Institute of Standards and Technology (NIST) maintains databases for standardizing thermometers.

Zero kelvin corresponds to -273.15 degrees Celsius and to -459.67 degrees Fahrenheit. A temperature difference of one kelvin corresponds to a temperature difference of one degree Celsius, and 9/5 = 1.8 degree Fahrenheit. To change from degrees Fahrenheit to degrees Celsius, use this link: Temperature Conversion Calculator.

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This page last updated 06/25/02