Mythical Myths #17: Humans radiate proportionately more than the Sun

Sometimes a statement which is perfectly true is called a myth on the basis of a misstatement. A case in point is “Bad astronomer” Phil Plait’s treatment of the statement in the above title in the post at  Q&BA: Pound for pound, are humans hotter than the Sun? | Bad Astronomy | Discover Magazine.

The correct statement of the mythical “myth” is that pound-for-pound (or ml-for-ml) the human body radiates more energy per second than the sun. Of course it’s not “hotter” nor does it *have* “more energy”, but it *loses* energy relatively more quickly because it has a relatively much larger surface area compared to its volume. This is just a consequence of the relative inefficiency of large spheres as radiators.  The reason for this is because any old cc in the middle of the sun may be as hot as hell but they all absorb almost as much radiation from their neighbours as they emit themselves, and it is only those near the surface which contribute photons which actually escape. So the idea of pulling them out to compare with us defeats the whole point of the exercise. It’s all part of the same theme which explains why elephants have big ears and why mice each day have to eat a much greater proportion of their body weight than we do. If I was as fat as the sun I’d be pretty hot in the middle too and that’s precisely because I would then be getting rid of heat proportionately less rapidly than I was generating it.

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