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Q&A: The Temperature of Space

27 Jun 2016, 07:01 UTC
Q&A: The Temperature of Space
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Question: How cold is it in outer space? — MF, Gotham City
Answer: That’s not as simple a question as you might imagine. Our normal definition of “temperature” is based on the collective behavior of molecules of gas or liquid in the environment. When you get the temperature online, from your smartphone, or from your outside thermometer, what’s being measured is the average kinetic energy of those air or liquid molecules. The equation for temperature in degrees kelvin (or simply kelvins) is:
T = mv2/3k where

m = average molecular mass
v = average molecular speed
k = Boltzmann’s constant = 1.38 × 10-23 J/K

The Kelvin scale is an absolute scale, with 0 K being the coldest temperature possible: 0 K is equivalent to a temperature of -273.15 °C or -459.67 °F. This temperature is referred to as absolute zero. It would be a state of matter in which all molecular motion has stopped. We could never cool something to that temperature because of quantum effects, but we can approach it. The coldest temperature achieved in the lab (to date) is 0.006 K.
In deep space, where very few molecules are present, we can’t define temperature in terms of ...

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