4 ms·

help me wrap my head around that. If you’re in -40 in a low pressure atmosphere, it doesn’t cool you down faster because there’s less mass for your heat to tran

help me wrap my head around that. If you’re in -40 in a low pressure atmosphere, it doesn’t cool you down faster because there’s less mass for your heat to transfer to? Does that mean things don’t cool down in a vacuum? Is there a weird curve where by at some point having less cold gas arounds you means you’ll cool down faster instead of slower?

danbruc 7y ago
Heat transfer happens by heat conduction and heat radiation, so even in a vacuum you will radiate heat away in the form of infrared photons, at least if the vacuum is not at a higher temperature. Heat radiation is however a less efficient process then heat transfer in a sufficiently dense environment. That is also an issue for spacecrafts, they need rather large radiators to radiate away excess heat into space.
- mytailorisrich 7y ago
  Vacuum does not have a temperature. You would probably need very little thermal insulation, if any, for a space walk around Pluto as heat from sun will be quite low as well.
  - danbruc 7y ago
    If you place a thermometer in space sufficiently far away from all heat sources, it will eventually reach 2.73 K, the temperature of the cosmic microwave background. I am not sure about the correct terminology but at least in some sense this is the temperature of outer space.
    - mytailorisrich 7y ago
      Vacuum has no temperature. What you describe is a black body spectrum 'temperature'.
      - danbruc 7y ago
        That is why I said that I am not sure about the precise terminology. But it still does not change the fact that an object placed in the vacuum of outer space will eventually reach the temperature of the cosmic microwave background, i.e. the temperature of the electromagnetic radiation filling outer space. Also not that I am not talking about any vacuum, I am specifically talking about vacuum of outer space.
        mytailorisrich 7y ago
        It does not change the fact that vacuum, any vacuum, has no temperature...
        danbruc 7y ago
        Also no perfect vacuum exists which renders this rather irrelevant for discussing what happens in real situations. I also did some reading to figure out the correct terminology - it is certainly correct to say that a perfect vacuum has no thermodynamic temperature as it is defined by the state of motion of the particles making up the system you want to assign a temperature to, however I am still not convinced that it is wrong to associate a temperature with a vacuum based on the electromagnetic radiation filling it.
        mytailorisrich 7y ago
        Yes, vacuum has no temperature. The energy of any radiation that may be going through a vacuum at a given instant is not a property of the vacuum (and is not an actual temperature). I'll leave it here as I think I have repeated the same thing enough though I am not sure it has been heard.
        danbruc 7y ago
        You keep repeating a point I never disagreed with, a perfect vacuum has no thermodynamic temperature. My issue with that is that I think it is a too narrow viewpoint for the comment I initially replied to. If one understands temperature as what a thermometer measures, then the temperature of a vacuum will be the temperature of its walls, it will not magically show »undefined« because you insist that temperature means thermodynamic temperature.
Syssiphus 7y ago
I think that property of a vacuum is already used in a day-to-day object. https://en.wikipedia.org/wiki/Vacuum_flask https://en.wikipedia.org/wiki/Vacuum_flask
colordrops 7y ago
That is correct, things don't cool down easily in a vacuum. Overheating is a problem on space vehicles. Thermal drinking bottles use a vacuum layer to keep heat in.
dsfyu404ed 7y ago
You lose/gain heat through conduction and radiation. Eliminating/reducing the atmosphere or making it out of something less conductive or lower specific heat reduces the speed at which the vibrating molecules of your body transfer kinetic energy to or gain energy from the molecules of the surrounding environment. The vast majority of heating/cooling that people experience in their day to day lives is done through conduction from the earth's atmosphere so in most situations you'd lose heat more slowly on Mars even if it is colder. It's kind of like the difference between being in cold air and cold water.
jandrese 7y ago
You lose out on convection and your heat loss has to be almost entirely through black body radiation instead. Astronauts have to work harder to stay cool than to stay warm, especially if the sun is shining on them.
Symmetry 7y ago
Vacuums make very good insulators, that's how a thermos works. Any cool gas is cooling you down but the denser it is the faster you cool down.
dotancohen 7y ago
One of the major sources of headaches for designing satellites is thermal management. In fact, during some weeks of the year the Space Shuttle could not visit the International Space Station because at the ISS inclination, the Shuttle would have spent too much time in the sun. The ISS, Space Shuttle, and other satellites have large radiators to cool them down.
ars 7y ago
> help me wrap my head around that Think about when it's cold, and when it's cold and windy. Low pressure air is like "anti" wind, even less cold then no wind on earth.
- b_tterc_p 7y ago
  So windchill is better interpreted as you will lose body heat as if it were this temperature without wind, but the actual temperature is still the same?
  - ars 7y ago
    Pretty much. You lose body heat at a rate that depends on the temperature, air pressure, wind, humidity, and maybe more, for example the thermal emissivity of the objects around you (and of yourself). If you set air pressure and humidity to "standard" values, and wind to zero, you can express the combination of other values as if they were a temperature, and call that windchill. Of all the variables wind is most important, since the rest don't vary very much on earth. But air pressure does vary on Mars, and thermal emissivity varies in space.

danbruc 7y ago

Heat transfer happens by heat conduction and heat radiation, so even in a vacuum you will radiate heat away in the form of infrared photons, at least if the vacuum is not at a higher temperature. Heat radiation is however a less efficient process then heat transfer in a sufficiently dense environment. That is also an issue for spacecrafts, they need rather large radiators to radiate away excess heat into space.

mytailorisrich 7y ago
Vacuum does not have a temperature. You would probably need very little thermal insulation, if any, for a space walk around Pluto as heat from sun will be quite low as well.
- danbruc 7y ago
  If you place a thermometer in space sufficiently far away from all heat sources, it will eventually reach 2.73 K, the temperature of the cosmic microwave background. I am not sure about the correct terminology but at least in some sense this is the temperature of outer space.
  - mytailorisrich 7y ago
    Vacuum has no temperature. What you describe is a black body spectrum 'temperature'.
    - danbruc 7y ago
      That is why I said that I am not sure about the precise terminology. But it still does not change the fact that an object placed in the vacuum of outer space will eventually reach the temperature of the cosmic microwave background, i.e. the temperature of the electromagnetic radiation filling outer space. Also not that I am not talking about any vacuum, I am specifically talking about vacuum of outer space.
      - mytailorisrich 7y ago
        It does not change the fact that vacuum, any vacuum, has no temperature...
        danbruc 7y ago
        Also no perfect vacuum exists which renders this rather irrelevant for discussing what happens in real situations. I also did some reading to figure out the correct terminology - it is certainly correct to say that a perfect vacuum has no thermodynamic temperature as it is defined by the state of motion of the particles making up the system you want to assign a temperature to, however I am still not convinced that it is wrong to associate a temperature with a vacuum based on the electromagnetic radiation filling it.
        mytailorisrich 7y ago
        Yes, vacuum has no temperature. The energy of any radiation that may be going through a vacuum at a given instant is not a property of the vacuum (and is not an actual temperature). I'll leave it here as I think I have repeated the same thing enough though I am not sure it has been heard.
        danbruc 7y ago
        You keep repeating a point I never disagreed with, a perfect vacuum has no thermodynamic temperature. My issue with that is that I think it is a too narrow viewpoint for the comment I initially replied to. If one understands temperature as what a thermometer measures, then the temperature of a vacuum will be the temperature of its walls, it will not magically show »undefined« because you insist that temperature means thermodynamic temperature.

Syssiphus 7y ago

I think that property of a vacuum is already used in a day-to-day object. https://en.wikipedia.org/wiki/Vacuum_flask https://en.wikipedia.org/wiki/Vacuum_flask

colordrops 7y ago

That is correct, things don't cool down easily in a vacuum. Overheating is a problem on space vehicles. Thermal drinking bottles use a vacuum layer to keep heat in.

dsfyu404ed 7y ago

You lose/gain heat through conduction and radiation. Eliminating/reducing the atmosphere or making it out of something less conductive or lower specific heat reduces the speed at which the vibrating molecules of your body transfer kinetic energy to or gain energy from the molecules of the surrounding environment. The vast majority of heating/cooling that people experience in their day to day lives is done through conduction from the earth's atmosphere so in most situations you'd lose heat more slowly on Mars even if it is colder. It's kind of like the difference between being in cold air and cold water.

jandrese 7y ago

You lose out on convection and your heat loss has to be almost entirely through black body radiation instead. Astronauts have to work harder to stay cool than to stay warm, especially if the sun is shining on them.

Symmetry 7y ago

Vacuums make very good insulators, that's how a thermos works. Any cool gas is cooling you down but the denser it is the faster you cool down.

dotancohen 7y ago

One of the major sources of headaches for designing satellites is thermal management. In fact, during some weeks of the year the Space Shuttle could not visit the International Space Station because at the ISS inclination, the Shuttle would have spent too much time in the sun. The ISS, Space Shuttle, and other satellites have large radiators to cool them down.

ars 7y ago

> help me wrap my head around that Think about when it's cold, and when it's cold and windy. Low pressure air is like "anti" wind, even less cold then no wind on earth.

b_tterc_p 7y ago
So windchill is better interpreted as you will lose body heat as if it were this temperature without wind, but the actual temperature is still the same?
- ars 7y ago
  Pretty much. You lose body heat at a rate that depends on the temperature, air pressure, wind, humidity, and maybe more, for example the thermal emissivity of the objects around you (and of yourself). If you set air pressure and humidity to "standard" values, and wind to zero, you can express the combination of other values as if they were a temperature, and call that windchill. Of all the variables wind is most important, since the rest don't vary very much on earth. But air pressure does vary on Mars, and thermal emissivity varies in space.