space and heat

[shortround]

do vacuums have a variable temperature? i'm sure i heard somewhere that space (ie. vacuum) is freezing cold. if this is the case then how does the heat from the sun reach the earth if its already 'blocked' by the vacuum of space?

[Caladon]

The vacuum of space has a temperature, depending on how close a heat source is i.e a star. In the shade of a star it is sub zero temperatures. In the sun it is hundreds of degrees. Our Sun heats up the Earth because of the distance. The heat is from light energy emitted from the Sun, which would be proton radiation (light) and heat. So if nothing is in the way of the Earth then yes, the Sun heats the Earth up. You can try something...hold up your pillow or something thick infront of the sun, so your head is in the shade. Your head will feel cool. As soon as you take it away your face feels the Suns immense heat and power. Same prinicple as space. Hope that helps somewhat

[jenstar]

In a perfect vacuum there would be no heat, that much is correct. However, space is not a perfect vacuum, hence why heat can travel through it.

[Hippy]

Let us not forget that heat travels in three ways; conduction, convection and radiation. Conduction requires objects to be solid or liquid and in contact with the heat source, convection requires a heated gas or liquid to move to propagate the heat, and radiation does not require a solid, liquid or gas, and is thermal energy transmitted in the form of waves (esp. electromagnetic waves) or moving subatomic particles.

So to the original question, a pure vacuum does not have a temperature, as there will be no solid, liquid or gas to hold the heat. If you plonk a thermometer (or other measuring device) then there is no longer a vacuum. Further, if radiation falls on the thermometer and you detect the presence of heat by a rise in temerature then you are measuring the temperature of the thermometer, not that of the vacuum.

[sft42]

My Dyson is always warm cause it sits in the cupboard where the hot water tank is.....does that help?

[shortround]

thanks for the answers peeps. it makes things a whole lot clearer.

[incitatus]

in physics the "temperature" of a vacuum is defined in terms of the amount of radiation passing through it. So although there is no thermodynamic transport, there is energy present, and so a temperature of sorts on the kelvin scale. i think space averages out to about 5 kelvin.

[Gef]

When we measure temperature we are measuring the amount of thermal (kinetic) energy of the particles in the substance. Since, by definition, a vacuum contains no matter then it has no thermal energy. Infra-red electromagnetic radiation can travel through a vacuum and heats up any substance (like the Earth) that absorbs it. Outer space is not a true vacuum and has enough matter in it to give an average temperature of 3K (-270C).

[incitatus]

gef you are falling into the trap of assuming that a) a vacuum is empty and b) that what we measure is what is real. you would not be able to stick a thermometer into a vacuum and tell what temperature it is at, but this does not mean that it has no kelvin temperature, i.e. contains no energy. a vacuum is a very busy place, containgin all sorts of virtual particel pairs, of which electrons and photons are perhaps the most common. classical physics doesnt allow for these but then classical physics is a pile of dingoes kidneys. the temperature of a vacuum is the sum of the energy in it. which includes the energy tensor across it.