# Naked Science Forum

## Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Fortran on 14/05/2009 22:03:24

Title: What is the temperature in space?
Post by: Fortran on 14/05/2009 22:03:24
I heard it again, and it really gets to me,

"The astronauts experience a temperature change from +200C to -200C"  - BOllocks"

The temperature of space is NOT 10 or 50 or 100 Kelvin, it is space, it has no temperature.
Temperature is a parameter of matter, it's about how atoms wobble about!, space does not wobble about!

When an astronaut does a space walk energy from the sun is absorbed by his/her suit and may indeed raise the temperature then, when in shade, heat will be radiated from the suit but like a vacuum flask heat is only lost through radiation and not convected or conducted away.

There, I got that off my chest! now who agrees with me?

Title: Re: What is the temperature in space?
Post by: syhprum on 14/05/2009 22:13:38
In the vicinity of the Earth the black body temperature is about 250°K i.e that is the temperature that a body will acquire when its adsorption and radiation is in balance.
Away from any stars the temperature is that of the CMBR about 2.73°K which is the red shifted radiation left over from the 'big bang'
Title: Re: What is the temperature in space?
Post by: Bored chemist on 14/05/2009 22:33:55
It's difficult to define the temperature of a vacuum. Who cares? since even space isn't a perfect vacuum, you just measure the temp of the few atoms that are left. They will, of course, have energies derived from the radiation in their environment as pointed out before.
Title: Re: What is the temperature in space?
Post by: Vern on 14/05/2009 22:34:34
Maybe they are reporting the difference in the read out of a temperature measuring device when it is moved from the sunny side to the shady side. [:)]
Title: Re: What is the temperature in space?
Post by: syhprum on 14/05/2009 22:46:46
If you define temperature by the velocity of the odd particle that is zipping about it could well be billions of degrees.
Title: Re: What is the temperature in space?
Post by: Fortran on 14/05/2009 23:34:39
If you put a thermometer in space it will only read it's own temperature and not that of free space, as I said temperature is an attribute of matter, radiation from the sun may heat up a thermometer but even in strong sunlight space has no temperature, the thermometer will though.
Title: Re: What is the temperature in space?
Post by: lyner on 15/05/2009 00:32:54
The definition of temperature is the average kinetic energy of the particles. There are particles throughout Space so there is a temperature, by that definition.
It is another matter to describe the effect of this 'temperature' on an object placed there. Rate of heat transfer and effective heat capacity are factors which also need to be considered.
As syphrum says, the effect of radiation from other sources will be the dominant one.
Title: Re: What is the temperature in space?
Post by: LeeE on 15/05/2009 02:53:01
I heard it again, and it really gets to me,

"The astronauts experience a temperature change from +200C to -200C"  - BOllocks"

The temperature of space is NOT 10 or 50 or 100 Kelvin, it is space, it has no temperature.
Temperature is a parameter of matter, it's about how atoms wobble about!, space does not wobble about!

When an astronaut does a space walk energy from the sun is absorbed by his/her suit and may indeed raise the temperature then, when in shade, heat will be radiated from the suit but like a vacuum flask heat is only lost through radiation and not convected or conducted away.

There, I got that off my chest! now who agrees with me?

You are correct insofar as a vacuum has no temperature, because temperature is a property of matter, being the kinetic energy of the particles to which sophiecentaur refers.  Space, however, is not a vacuum, at least certainly not in the vicinity of a star or any planet with an atmosphere.

The situation is similar in some ways to our upper atmosphere.  Although everyone thinks that it is 'cold' at high altitudes, this is just because there isn't very much 'air' up there.  What molecules you do find at high altitude though, are likely to be 'hotter' than those you'll find at lower altitudes.
Title: Re: What is the temperature in space?
Post by: Fortran on 15/05/2009 12:41:35
And for the second part a thermometer dipped in hot coffee will only measure it's own temperature, and it's the same in space, a thermometer will only indicate it's own temperature.  Even a rarified gas is unlikly to alter the thermometer temperature (much)which will settle at a point where energy absorbed, balances with energy lost.

Either way I feel it is technically incorrect to say astronauts go from +200 to -200 when moving into the shade.

Title: Re: What is the temperature in space?
Post by: LeeE on 15/05/2009 17:00:03
I think the issue is really that the majority of people, who don't really understand science, wouldn't understand it if it was described more accurately.  As it is, even though we know the reporting is actually incorrect, we know what they're trying to say, so while it's not perfect it does manage to get the message across.

In some ways, it's no different to what we go through when we start learning science;  at school we initially learn that everything is made up from atoms, then as we progress to higher levels the atom is broken down to electrons, neutrons and protons.  It's only once we reach relatively high-level physics that we learn about the rest of the vast array of sub-atomic particles, such as quarks and neutrinos etc.
Title: Re: What is the temperature in space?
Post by: JP on 15/05/2009 17:58:12
Actually, the original quote isn't too bad.  It says they "experience a temperature change," which is different from "the temperature of space is..."  They're talking about the temperatures experienced by the suit, or by the astronauts if they fell out of their suits, which are certainly well-defined.
Title: Re: What is the temperature in space?
Post by: Fortran on 15/05/2009 18:11:52
Actually, the original quote isn't too bad.  It says they "experience a temperature change," which is different from "the temperature of space is..."  They're talking about the temperatures experienced by the suit, or by the astronauts if they fell out of their suits, which are certainly well-defined.

uh?

If the astronaut 'fell out of his suit' he would not suddenly experience temperatures of minus 200C - think about a vacuum flask, no air, no light, a vacuum, yet the hot drink inside remains warm, (yes I know why)  same in space the astronaut would slowly lose heat as it was radiated, he would not feel a sensation of cold until a certain amount of heat had been radiated away.

Title: Re: What is the temperature in space?
Post by: JP on 16/05/2009 01:35:26
True enough.  I see your point, but to me the concept of thermal equilibrium just seems to me to be the most natural way to describe the temperature the astronaut might "experience."
Title: Re: What is the temperature in space?
Post by: Soul Surfer on 16/05/2009 10:49:04
In space and on the earth there are at least three "temperatures"  and we are all familiar with them. firstly there is the temperature of the gas around us.  Then there is the temperature induced by the radiation(sunlight) falling on us and thirdly there is the temperature of the sky and other objects around us.  This is most noticeable moving from sunshine into shade and moving.
On the earth there is also a "wind chill" factor but this would not apply in space.   In space the temperature of the atoms near the earth is very high but there are not many of them so they are not important.  The two critical ones are the sunlight on the sunny side of the space suit and the coldness of the microwave background radiation on the shady side so these extremes are quite possible.

Title: Re: What is the temperature in space?
Post by: litespeed on 16/05/2009 14:51:09
Another Two Cents - The Temperature of Space

Of course empty space has no temperature, but as described above not all space is empty. Further, I don't know of anyway to measure the mean temperature of any particular volume let alone intergalactic space.

However, don't all objects emit radiant energy that is generally measured in Degrees Kelvin? For instance, fluorescent light tubes have a color temperature measured in Kelvins. Theoretically, isn't that the temperature of the particles emitting the light. However, we do not feel it because the mass of emitting particles is so low there is next to no actual heat transfer in joules (?).

Title: Re: What is the temperature in space?
Post by: syhprum on 16/05/2009 18:24:29
This is an interesting point, the colour temperature of my monitor screen is rated at 6000°K but when I put my hand on it it feels quite cool, I guess that somewhere in the phosphor atomic transitions are taking place induced by the electron beam that would require a temperature of 6000°K to induce them thermally.
Title: Re: What is the temperature in space?
Post by: Bored chemist on 17/05/2009 15:18:03
Just as an exercise, those hwo enjoy such things might want to calculate the "temperature" of the electrons in a cathode ray tube with a kinetic energy of for example 10KeV.
Title: Re: What is the temperature in space?
Post by: syhprum on 17/05/2009 20:30:49
One ev is equivalent to 11604°K hence the 27KV electrons zipping down the CRT of my monitor have an effective temperature of 313,000,000°K, hot enough to generate X Rays.
Thank goodness for colour screen mesh a thick lead glass!
Title: What is the temperature in space?
Post by: lyner on 18/05/2009 00:37:18
One ev is equivalent to 11604°K hence the 27KV electrons zipping down the CRT of my monitor have an effective temperature of 313,000,000°K, hot enough to generate X Rays.
Thank goodness for colour screen mesh a thick lead glass!
I'm not arguing with that, necessarily, but if potassium can be induced to produce photo electrons with the light from a lamp at 5kK and the work function is 2.3V, how does that square with your figure. What have I missed?
Is it to do with the frequency distribution and the 'average'?
Title: What is the temperature in space?
Post by: syhprum on 18/05/2009 07:27:56
It is indeed a puzzle why such apparent overkill is needed but I have encountered monitors where due to a PSU fault the EHT has dropped to 10KV and the brightness is much reduced

Light from a 5000°K thermal source would produce Photons of a peak enegy of 0.43ev but as you say they will excite Potassium atoms that require 2.3V presumably the Photons are produced with a range of energies going up as high 2.3ev

This of course assumes your source of radiation is thermal I do not think if it was monochromatic the Potassium would be excited
Title: What is the temperature in space?
Post by: Raghavendra on 18/05/2009 10:53:21
I don't think that space has a temperature same at all time...

But, i agree that space has a certain temperature. It is a vacuum, joint particles doesn't strech, same principle works out here... In vacuum has a specific temperature.
it has not yet revealed.
Title: What is the temperature in space?
Post by: lyner on 18/05/2009 11:32:55
syphrum
I guess that most of the energy from a thermal source is wasted when hitting potassium. With only a red hot source, you might still expect the occasional photon with enough energy to release a photo-electron.

I wonder if, when the beam volts drop, the penetration of electrons into the phosphor material is less - producing less light. Or are there some double energy transitions in the conversion from KE to visible photons?