I think some of the confusion arises because of vacuum thermos bottles, which are really efficient at holding onto their heat. But how they work is a bit complicated. They deal with conduction and convection losses by having the vacuum barrier between the contents and the outside. As to radiation, they rely on a reflector that's part of the vacuum bottle, which has the effect of greatly slowing the rate of heat loss by radiation.
So the vacuum thermos avoids radiation heat loss, not because of the vacuum, but with a reflector. That works in space too -- many orbiting telescopes use reflectors to keep the sun's heat energy from heating up the sensors and spoiling their performance.
But a vacuum is a pretty good medium for heat loss by radiation. The moon's surface, heated to several hundred degrees Celsius during the lunar daytime, drops to 26 Kelvins after a few (earth) days of darkness (26 degrees above absolute zero). That's a new figure, lower than had been realized, and seven degrees colder than the surface of Pluto.
Interesting speculation. I can't say whether it was related in my case - certainly it wasn't first-order (discussions I am very vaguely recalling revolved around satellites, but it was at least a decade and a half ago), but it could easily have been a cause of the meme in the first place.
I do recall someone explicitly stating that radiation is a poor means of losing heat compared to convection and conduction - which seems to just be wrong.
> I do recall someone explicitly stating that radiation is a poor means of losing heat compared to convection and conduction - which seems to just be wrong.
Yes -- it's a common belief, and it's wrong. Under clear skies after dark, objects on the surface that are convectively coupled to the atmosphere will quickly fall below air temperature because of radiation heat loss, which can produce what is called "radiation fog", so named because it's caused by the air being cooled by the ground, which in turn has been cooled by direct radiation into space.
I think some of the confusion arises because of vacuum thermos bottles, which are really efficient at holding onto their heat. But how they work is a bit complicated. They deal with conduction and convection losses by having the vacuum barrier between the contents and the outside. As to radiation, they rely on a reflector that's part of the vacuum bottle, which has the effect of greatly slowing the rate of heat loss by radiation.
So the vacuum thermos avoids radiation heat loss, not because of the vacuum, but with a reflector. That works in space too -- many orbiting telescopes use reflectors to keep the sun's heat energy from heating up the sensors and spoiling their performance.
But a vacuum is a pretty good medium for heat loss by radiation. The moon's surface, heated to several hundred degrees Celsius during the lunar daytime, drops to 26 Kelvins after a few (earth) days of darkness (26 degrees above absolute zero). That's a new figure, lower than had been realized, and seven degrees colder than the surface of Pluto.