Temperature in Space

[Stonejaw]

Ok a buddy of mine and I were having a discussion about what the actual tempurature of space is. Now I understand that it is around 3K everywhere in space and never gets to absolute 0.
But we were arguing that if you took a thermometer into our orbit as if an astronaut took it out with him what the tempurature would read if it was in direct sunlight. I thought it would be at least 100 degrees C while he thought it would read 0.
Although I know even in darkness the thermometer would take forever to reach 0 as it has no way of radiating its heat to anything if nothing is touching it.

So what would a thermometer read in our orbit in direct sunlight?

 

[PottedMeat]

Originally posted by: Stonejaw

So what would a thermometer read in our orbit in direct sunlight?

Hmm I would think it rise to how ever much incident energy hits it from the sun and reradiate as infrared. But then again I'm thinking the longer you expose it the hotter it gets, but only if reradiation < the incident sunlight. Now I'm confused. However I seriously doubt it's zero.

edit: oh assuming the glass is strong enough not to rupture. or maybe its one of those bimetallic strip ones.

 

[CycloWizard]

It depends on a lot of things, but you're on the right track. How close to the sun? What color is it?

 

[DrPizza]

It doesn't need something touching it to "radiate" heat away.
Also, zero what? 0K? 0 degrees C? 0 degrees F? It'll never hit 0K. Nothing ever will.

 

[Nathelion]

http://www.grc.nasa.gov/WWW/K-...ng_the_temperature.htm

Might provide some insight

 

[PolymerTim]

Well, there's a few things to consider, and I had to do a little review myself to straighten out some things, so wikipedia is a good place to start.

First, temperature is a property of mass and therefor, pure vacuum has no temperature because there is no mass. That being said, there is pretty much always some mass in a reasonably sized volume of space and the vacuum is not perfect.

Next, keep in mind that thermal energy or heat can be transferred through conduction, convection, or radiation.

For your scenario of space, I think convection will be negligible since it deals primarily with a flowing medium such as water or air. Similarly, conduction refers to heat transferred through direct contact of masses (like in metals). This would occur in space any time a particle or molecule of gas collides with your test object. Energy is transferred during the collision just like in NASCAR. Again, since this effect reduces to zero in a perfect vacuum, I'm guessing this is negligible in space, so we are left primarily with radiation.

So, to oversimplify thermal radiation, lets just say that your object in space is constantly releasing thermal radiation and simultaneously absorbing energy from the sun, the earth, and any other objects nearby with a measurable mass and energy. The amount of energy released and absorbed by your test object will depend greatly on the molecular characteristics of the object itself since it will be likely to absorb some wavelengths of radiation more than others, which may or may not correspond well to the wavelengths of energy being released by the nearby radiating objects. At equilibrium, the object will balance the energy it is releasing and absorbing and come to a rest temperature dependent on all the above mentioned variables.

One example wikipedia had was interesting. Ballpark figures of course: a typical person will radiate about 1000W of energy, but in a typical room-temperature room, will receive back about 900W from the room resulting in a net loss of 100W due to radiation.

More closely related to your example, under "temperature in a vacuum" from my first link, if you consider your thermometer to be a perfect "black body", meaning it absorbs all wavelengths of light (none is reflected or passes through it), and place it in orbit around the earth then it should equilibrate to about 281 K (+8 °C), which is about the same as the average temperature of the earth. If the thermometer were to stay in the shade of the earth, then it would end up closer to 236 K (-37 °C), due primarily to radiation from the earth. And finally, as you mentioned, if you move this black body thermometer into deep space, then it would essentially equilibrate with the cosmic background radiation at about 2.725 K.

 

[silverpig]

It's a very simple calculation to do.


Look here (wikipedia) under the section "Temperature relation between a planet and its star" to see how its done. The framework is there. You can put in your estimates for the geometry of your thermometer and what not. Assuming it's non-spherical it should be a little lower than 14 C.

 

[johnpombrio]

This is one of those Richard Feynman questions. He always took a look at the obvious implications first. How does a thermometer work, assuming it is the old glass with mercury kind or the kind with a spring in it. Trillions of molecules of air bump into these devices and transfer their heat to them. Period. Remove the molecules, remove the heat transfer. The thermometers drop like a stone.
Vacuum is a GREAT insulator. However, a human naked in space with freeze very quickly. Why? Because we RADIATE heat away from our bodies as infrared radiation. Low pressure really does not have much to do with it, and NO, your eyeballs won't pop out!

 

[PolymerTim]

Originally posted by: johnpombrio
This is one of those Richard Feynman questions. He always took a look at the obvious implications first. How does a thermometer work, assuming it is the old glass with mercury kind or the kind with a spring in it. Trillions of molecules of air bump into these devices and transfer their heat to them. Period. Remove the molecules, remove the heat transfer. The thermometers drop like a stone.
Vacuum is a GREAT insulator. However, a human naked in space with freeze very quickly. Why? Because we RADIATE heat away from our bodies as infrared radiation. Low pressure really does not have much to do with it, and NO, your eyeballs won't pop out!

That's partly true, but your leaving out the radiative energy striking the thermometer or your body from other sources such as the sun. Funny how, in the same post, you specifically state "Remove the molecules, remove the heat transfer" and then point out that our bodies can radiate heat away.

While low pressure may not be directly involved, it is related to a lack of gas molecules which reduces the convective heat transfer as you mentioned. Also, you might consider special cases like, if there is a volatile liquid on a surface exposed to the vacuum (such as water in your mouth), then the vacuum will significantly accelerate evaporation leading temporarily to a much colder surface.

And while your eyeballs won't pop out, your blood and other body fluids can boil leading your body to bloat up to twice its normal size!
http://en.wikipedia.org/wiki/V..._on_humans_and_animals

 

[gururu2]

thermometers work because the density of the substance inside of them is sensitive to temperature. depending on the substance, there will be a temperature at which the substance solidifies. for mercury, that temperature is -39° C or 234 Kelvin. if the substance solidifies, then the substance will not 'flow' past the bottom marker.

that aside, temperature is simply a property directly related to the heat content of a system. heat content is directly related to the energy of the molecules in that system. due to lack of molecules, space exhibits a lack of energy, and hence a lack of heat.

the only temperature one could measure in space accurately would be the temperature of the thermometer which is unrelated to the surroundings.

 

[KillerCharlie]

Originally posted by: Stonejaw

...no way of radiating its heat to anything if nothing is touching it.

Several people already posted about this, but you might want to take some basic physics courses.

 

[silverpig]

Originally posted by: gururu2
thermometers work because the density of the substance inside of them is sensitive to temperature. depending on the substance, there will be a temperature at which the substance solidifies. for mercury, that temperature is -39° C or 234 Kelvin. if the substance solidifies, then the substance will not 'flow' past the bottom marker.

that aside, temperature is simply a property directly related to the heat content of a system. heat content is directly related to the energy of the molecules in that system. due to lack of molecules, space exhibits a lack of energy, and hence a lack of heat.

the only temperature one could measure in space accurately would be the temperature of the thermometer which is unrelated to the surroundings.

Not all thermometers work that way. Look up Ruthenium Oxide. We use it to measure down to 8 milli-Kelvin.

And while there are no molecules to equilibrate with, there is radiation which has a certain temperature.

 

[f95toli]

Slightly OT
Silverpig: I would not really trust a RuO2 down to 8 mK. The reproducibility seems to be pretty bad below 20 mK. I have tried "calibrating" one using our nuclear orientation setup, but the resistance vs. temperature seems to change slightly between different cooldowns. I have been told this is a known problem with RuO2 (although I don't think germanium is any better).
However, Lakeshore is selling a new type that they claim works down to 10 mK (apparantly they will soon even be able to sell sensors that are calibrated down to 10 mK), Is that the type you are using?
We have been thinking of buying one that is calibrated between say 20 mK and 2K.

On topic
Gurguru2: This is how SOME thermometers work including the old mercury based ones, but most modern thermometers instead use the temperature dependence of the current-voltage charachteristics of e.g. a biased silicon diode. This means means that we are in effect actually measuring the temperature of the "electrons" in the solid, but at high temperatures this is effectivly the same as the temperature of the lattice (the phonons) since the scattering times tend to be extremely short.

 

[silverpig]

Originally posted by: f95toli
Slightly OT
Silverpig: I would not really trust a RuO2 down to 8 mK. The reproducibility seems to be pretty bad below 20 mK. I have tried "calibrating" one using our nuclear orientation setup, but the resistance vs. temperature seems to change slightly between different cooldowns. I have been told this is a known problem with RuO2 (although I don't think germanium is any better).
However, Lakeshore is selling a new type that they claim works down to 10 mK (apparantly they will soon even be able to sell sensors that are calibrated down to 10 mK), Is that the type you are using?
We have been thinking of buying one that is calibrated between say 20 mK and 2K.

On topic
Gurguru2: This is how SOME thermometers work including the old mercury based ones, but most modern thermometers instead use the temperature dependence of the current-voltage charachteristics of e.g. a biased silicon diode. This means means that we are in effect actually measuring the temperature of the "electrons" in the solid, but at high temperatures this is effectivly the same as the temperature of the lattice (the phonons) since the scattering times tend to be extremely short.


Well our fridge only made it down to 8 mK the one time when the guy from Oxford was there. We can get down to 30 mK usually, and I think we've hit 20 a few times since...

Either way the point I was making is you don't need a liquid to expand in order to measure temperature