Science Questions

Why is it cold in Space when the Sun is hundreds of thousands degrees C?

Sun, 20th Feb 2011

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Megan Zoe Wilson, via Facebook asked:

Why is it cold in Space when the Sun is hundreds of thousands of degrees C?


Dave -   The Sun is incredibly hot, but the Sun is not throughout the whole of space.  So, when you're sitting in space, in the Earthís orbit, you're getting hit by about the same amount of sun that you get if you're sitting on Earth, but the rest of you can see deep dark space which is about -270 degrees centigrade.  So, you radiate heat into the deep dark space because anything warm glows in the infrared; and you're getting hit by sunlight, and the balance of those two is the temperature youíll sit at.  In the Earthís orbit I think itís a bit below 0 degrees centigrade.


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I think because there is no atmosphere. Warm it is something transmission between particles of the air (not necessarily particles of the air that can be anything between water and metal or anything what have got skill transmission heat) who move and collide and transmission energy or heat. If we have got no atmosphere in a space so we have got no move, no collide, no energy and heat. juhuhu., Fri, 25th Feb 2011

Yep, I think you caught it juhuhu. Temperature is when something 'jiggles'. The more the molecules and atoms 'jiggle' the hotter we should find it. In space we don't have anything that can 'jiggle', or at least very little.

When a sunbeam 'propagates' it will do so until something, like that molecule/atom comes in its way. When the sunbeam hit that molecule we call it a 'interaction' meaning that the sunbeam now is 'destroyed', more or less annihilated. And the sunbeams 'energy' and momentum, as well as angular polarization (like its 'spinning') all transfer into that molecule/atom that now will react by 'jiggling' even worse :)

When 'some/every/thing' stops jiggling we will find it to be very cold, as in the grave.

And this I have from the best of sources :)
TNS no less. yor_on, Sat, 26th Feb 2011

The sun is a very large mass of matter which interacts with itself to produce nuclear reactions but space has become so stretched since the big bang that the energy in it has also been stretched so that it is now 'diluted' and weak and therefore colder. abacus9900, Sun, 27th Feb 2011

Juhuhu, sorry, that can't be technically correct. if space is a vacuum, without particles to transfer heat. How does heat get from the sun to Earth.
Equally if heat can travel unimpeded through a vacuum, then theoretically it should be as hot on Mars as it is on Jupiter. The only difference being that on Earth we have atmosphere, which acts to magnify and store heat.
If you theory is correct, then there must be particles in the space void to enable heat transfer and if so, what are they and how can we use them Davedownunder, Thu, 11th Jul 2013

Heat is radiated from the sun primarily with light.  As the sun is very hot, the radiated light is primarily in the UV and visible spectra. 

The intensity of the sunlight falls off with the square of the distance.  So, Mercury and Venus get more intense sunlight than Earth.  Mars and the outer planets get less intensity of sunlight. CliffordK, Thu, 11th Jul 2013

Space is neither hot nor cold, because it is literally nothing. Temperature is the mean energy of molecules: no molecules, no temperature!

Objects in a vacuum (space) radiate heat and receive heat radiated from other objects. The intensity of received radiation decreases with the square of the distance from the source. So if you are a long way from the sun, you will radiate more heat that you receive, and you will cool down.

The trick with near-solar spacecraft is to balance the heat input on the sun-facing side with the heat radiated from the shadow side to maintain an even internal temperature. A simple approach is to make the exterior with a pattern of high- and low-emissivity materials (even black and white paint) and have the ship rotate, but if you don't want it to rotate, you may need to include an active heat transfer system. alancalverd, Thu, 11th Jul 2013

Temperature can actually be defined as mean energy of particles, which also includes photons.  Because space is filled with photons left over from the big bang, we can compute its temperature: about -270 centigrade, as Dave said above.  This would be the temperature reached by a thermometer left in deep space. jpetruccelli, Thu, 11th Jul 2013

True. alancalverd, Thu, 11th Jul 2013

Good ole Jp hits the proverbial nail on the head yet once again; bravo my good man. That is quite correct. Nasa explains all that here Pmb, Thu, 11th Jul 2013

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