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superbob201 t1_jbyrhgx wrote

Temperature is a statistical quantity that happens to be proportional to average energy in a system of particles following a Maxwell-Boltzmann distribution. However, it is not proportional to average energy by definition. If the gas has a non-zero average velocity in your frame it is not following an MB distribution, so it's temperature is not proportional to its average energy in your frame.

As a side note, you would observe blackbody radiation that was red- or blue-shifted depending on your motion that could make the gas appear warmer or cooler.

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Chemomechanics t1_jbzkgtc wrote

> As a side note, you would observe blackbody radiation that was red- or blue-shifted depending on your motion that could make the gas appear warmer or cooler.

A hotter or colder body's blackbody radiation isn't simply shifted by a set amount, so this isn't true. You'd identify the same temperature with some overlaid bulk motion. I apologize; my statements were incorrect.

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superbob201 t1_jc04vlv wrote

One annoying thing about blackbody radiation is that is still looks like blackbody radiation after Doppler shifting. It's why the CMB has a blackbody temperature of 2.7K, even though it is coming from ionized hydrogen.

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