Thread: The temperature of outer space.

I think i may have put too much thought into this, but does outer space have a temperature?

I know it's cold. Really cold. And space itself cant be warm because theres nothing for radiation or energy to land upon and express itself as heat.

But does it have a median temperature?
If youre in a shadow, and closer to the sun is it the same as if youre were in a shadow and really far away from the sun?
Is there any heat given off by distant stars and galaxies that would collectively give space a steady base temperature?

It's about 3 degrees Kelvin out there...that's about -454 degrees F.

Originally Posted by Joe McCarron

I think i may have put too much thought into this, but does outer space have a temperature?

I know it's cold. Really cold. And space itself cant be warm because theres nothing for radiation or energy to land upon and express itself as heat.

But does it have a median temperature?
If youre in a shadow, and closer to the sun is it the same as if youre were in a shadow and really far away from the sun?
Is there any heat given off by distant stars and galaxies that would collectively give space a steady base temperature?

It's not really space itself that has a temperature, but rather the stuff in space that has a temperature. And as Dave E Eaton Sr. mentions, that stuff is mostly pretty cold . . .

Thank you, Coelacanth. I always appreciate and enjoy your input, but I did state that in my first post, almost word for word.

Oh well, little review never killed anybody. :P

Originally Posted by Joe McCarron

Thank you, Coelacanth. I always appreciate and enjoy your input, but I did state that in my first post, almost word for word.

Oh well, little review never killed anybody. :P

And you did indeed. Let me try to do a little better But only slightly better - consider this post to be the internet equivalent of a few calculations scribbled on a napkin, with ketchup stains all over. In other words, it should be set aside in favour of just about anything said by someone who actually knows something about the topic.

I looked up the temperature of Pluto at the University of Google, and one of the first links is this one, which tells me it ranges from 33 Kelvin to 55 Kelvin. The most exalted Wikipedia page tells me that at its farthest distance from the sun, Pluto is less than seven light-hours away. The nearest other star is something like 4 light-years away, or about 5,000 times farther. So even being ten times as far from the sun as Pluto is, by inter-stellar standards, still pretty close. And as the radiation from the sun ought to follow an inverse square law, if you are ten times as far from the sun as Pluto, then you ought to receive 1% as much radiation (per unit of cross-sectional area) as Pluto. If Pluto gets all of its heat from the sun (perhaps it gets some from internal sources, but assigning 100% to the sun gives us an upper bound), then the temperature might be 1/100 of the temperature of Pluto, or 0.55 Kelvin (taking the high temperature from the first link).

So my lunch-time napkin, covered with ketchup stains, analysis, suggests that for objects in interstellar space, the temperature due to heating from stars ought to be almost nothing, much less than one degree Kelvin. Now, there could be an awful lot wrong with this analysis - maybe there are places where stars are packed a lot more closely than around here, maybe many stars burn much more brightly than ours, maybe interstellar matter absorbs heat much better than Pluto does - I don't really now. But still, seems like it should be really, really low.

So I wonder if the 3K figure cited is from sources other than radiation absorbed from surrouding stars. Perhaps it is residual, interstellar matter was much hotter a long time ago, and is slowly radiating away its heat, but it hasn't finished yet? Or perhaps it is heated by some other process I don't understand. Or perhaps I have made some appalling error in my analysis. I don't know, but my first, quick napkin effort suggests to me the heat from stars ought to be almost nothing - less than 1K.

David Eaton, can you add anything to the 3K figure? Is this residual, from the beginning of the universe?

The other issue, which I can address somewhat more sensibly, is that to ask what is the median temperature, implicitly has to make some assumption about median over what? If we are talking about median unit of space, almost all space is very far from any star, and should receive very little heating. If we are talking about the median chunk of matter, a lot of matter (unless all that dark matter is real) is in or near stars, and should be hotter (a lot hotter?). I interpret your question to refer to the median unit of space.

As is most likely evident from the above, I really don't know too much about this, and should probably keep my mouth shut. But I will try to recover from my earlier showing in the thread

ETA - I seem to recall reading, years ago, the claim that a distance rock, planet, whatever, hardly blocks any of the light from across the universe headed in our direction, but taking the same rock or planet, grinding it into fine dust, and spreading it out, causes it to block quite a bit more effectively. So maybe using a planet as the benchmark is not reasonable; perhaps interstellar dust does really absorb radiation hundreds, or thousands, or more times more than a really big rock.

Originally Posted by Coelacanth

David Eaton, can you add anything to the 3K figure? Is this residual, from the beginning of the universe?

Cosmic microwave background radiation - Wikipedia, the free encyclopedia

Originally Posted by Coelacanth

David Eaton, can you add anything to the 3K figure? Is this residual, from the beginning of the universe?

Man, you are asking me to clean out the cob-webs, aren't you... As I recall, the BB had huge temperatures that have been dropping ever since...around 300,000 years after the BB it had cooled to around 3000 K...I would assume that as the universe continues to expand, the temperature will drop even more. The 3 K figure is probably more like 2.75 K but it's been such a long time I'm not sure...I do know it's not more than 3 K.

The temperature of the space between the galaxies is 2.7 K as evidenced by the Cosmic Microwave background radiation.

...it's hotter in the summer, i'm sure ( ;-q ), but the 2.72 K corresponds well to the ubiquitous 21 cm hydrogen radiation.

The mean temperature of the entire universe, as in put all the matter (which interacts with light - EM energy, including heat) in one spot, measure its mean temperature and then average it across the current volume of the universe? Is that what you mean? Well, if the photon-interactive "stuff" in the universe only comprises <5% of the known universe and its temperatures range from ~6 x 10^7 K to 2.7K (give or take), and most of it in the 2.7K range, it would still make it sort of lean on the chillier side - definitely mittens and scarves, if one were to go out for a stroll!