Daft question or not

[mog3768]

This might seem like a daft question, but why is space so cold. I was out yesterday observing the sun and after a while had to shelter from the heat. ( OK natural enough what you would expect, it is pretty close to us.)  But then I thought I would be out again in the late evening to look at the stars, millions and millions of them all in different states of evolvement but all radiating heat into space and they have been doing this for billions of years.

So were has all this heat gone? Why hasn't there been a slow build up?

Am I missing something obvious. If so, someone please point it out.

[PhotoGav]

That's a great question, exactly the kind of thought that late night staring at the stars generates, love it!

I have no real idea about the answer as I am a photographer not an astrophysicist. However, as for a build up of heat, my understanding from O-Level sciences is that nothing can be made, it can only be transferred from state to state. So if it heats up here, it cools down there... As I said, I'm no astrophysicist.... I'll get my coat.

[Scott]

Is it warm on earth because we have an atmosphere? heat is essentually caused by the rapid movement of atoms generating friction? in space ther is no friction? Daft answer? probably

[mog3768]

So  ar you thinking that space is just acting as a conduit to transfer heat and not absorbing any

[Scott]

mog3768, first let me quantify my answers by saying I'm only guessing .

My guess is that as space is empty, there is nothing to restrict the photons thereby causing friction (heat). when it hits our atmosphere it finds friction and causes heat.

PLEASE will someone who knows what they're talking about come and tell us the real reason . 

[Scott]

These guys probably have a better grasp than me 

http://helios.gsfc.nasa.gov/qa_sp_ht.html#coldspace

[Thalestris24]

Hi

It's just that space is virtually empty so has no heat capacity, and as pointed out above, it's our atmosphere that traps heat from the sun. It's pretty cold on mars because it's further away from the sun but also because it's atmosphere is very thin. It's very hot on venus because it's closer to the sun and because it has a very thick atmosphere. Things do heat up in space because of the sun and cool down when out of the sun - hence the big difference in temperature between the light and dark side of the moon.

Louise

[ronin]

What we generally experience as heat is kinetic energy from the atoms of the air, so in space this kinetic energy is not really present - no air.

You will get radiation from the sun but they is a measure of energy of the radiation and not until it hits something does this get transferred to kinetic energy. Photon is absorbed by an atom and it's kinetic energy goes up.

Our hot/warm days are when the atmosphere gets warmed up, the sunlight falling on us will get absorbed so we get hot from the absorbed radiation getting absorbed by our bodies.

In effect until the radiation is absorbed and so increases the kinetic energy of something do we experience Hot/Cold.

[oldpink]

like sound heat needs a medium to transfer through
and we all know in space no one can hear you scream
until the radiated heat reaches a medium its just energy

[ollypenrice]

A bit of an aside (or another way of looking at it) but, while space is cold, it is also a near vacuum and so is a good insulator. This seems paradoxical in a way.

There are also two ways of encountering temperature. An oven's air inside is about the same temperature as its metal sides. Put your hands into the air, sure, but don't touch the sides!

Olly

[PhotoGav]

I suppose there are plenty of 'hot spots' dotted around the universe where you would certainly warm up as you approached them... The Sun is a tiny and relatively cool star, so imagine approaching some of the mammoth white ones! You'd soon see where all the heat was out there...

Anyway, thank goodness it's not all gradually warming up - I know we shouldn't diss the summer, but I wouldn't want to work in temperatures like this all year, let alone increasing temperatures. Oh hold on, it is warming up (apparently) on Earth.......

[Zakalwe]

Space (a vacuum) isn't a good insulator of heat. If it was then the Sun's heat would never reach us!

There are 3 ways to transmit heat: Radiation, Conduction and Convection. In an atmosphere (such as ours) we feel heat as direct radiation from the Sun (and also from the ground/surrounding objects as they radiate heat), conduction (from the air and from touching hot objects) and convection (warm air currents). What a vacuum does do is eliminate two of those methods, conduction and convection, as both mediums need matter to conduct and convect. Th surrounding air also acts as an insulating blanket, preventing us from radiating our heat away. This is why we sweat, to remove heat by evaporation.

An object in the direct view of the Sun in space will quickly heat up, as the object absorbs heat radiation. This is why spacecraft are put in a barrel roll (Thermal Control Manoeuvre) to constantly present a different surface to the Sun. As the "hot" side rotates it is able to dump the heat load, again by convection, to space which is essentially a black-body.

Space itself is cold though- approx 3 Kelvin. The reason why it is not at absolute zero is due to the residual heat left over from the Big Bang.

The Universe is also a very big place, and it is getting bigger all the time. In comparison to the amount of matter in it, it is virtually empty (the average density of the Universe is very low) and there is a looong distance between heat emitting objects.

[mog3768]

I think Ronin has it, in that it needs to react with another body to transfer that heat and of course space is empty. ( at least present thinking says it is)

[Kropster]

Space has photons of different energies whizzing around, but the actual density is probably very low at any distance from a star.

The photons would transfer their energy to anything that absorbs them, like dust or astronauts, and have a heating effect on them..... but on average the heating effect on and radiation from a body give an overall low temperature (I think!).

[Alien 13]

I have been reading this and just had a thought, if the space in the universe is a vacuum why is it at 3 degrees kelvin anyway shouldnt it be zero with residual energy from the big band just that energy that is travelling through it.

If the space is not a perfect vacuum then why isnt it rapidly heating up.

Alan

[C7tsj]

Also, is space not filled with dark matter? Would this not mean dark matter can't conduct or at least hold onto the heat?

Perhaps another daft question...........

Mark

[Kropster]

I have been reading this and just had a thought, if the space in the universe is a vacuum why is it at 3 degrees kelvin anyway shouldnt it be zero with residual energy from the big band just that energy that is travelling through it.

If the space is not a perfect vacuum then why isnt it rapidly heating up.

Alan

I think it is a case of the radiation being at a wavelength that would be radiated by a 'black body' at a temperature of 3K.

[Thalestris24]

Empty space is empty - there's nothing to heat up! Radiation from the sun, stars, cosmic background just passes through it!

[Zakalwe]

I have been reading this and just had a thought, if the space in the universe is a vacuum why is it at 3 degrees kelvin anyway shouldnt it be zero with residual energy from the big band just that energy that is travelling through it.

It's not.

Space is, in the main, empty. When you point a detector at the sky the detector picks up the background glow at 3 Kelvin from the radiation that has been travelling since the Big Bang. Its like a much weaker version of the Sun....so what you are measuring is the last heat of the Big Bang and not space (as there is nothing to measure in Space!)

If the space is not a perfect vacuum then why isnt it rapidly heating up.

Why would it?

[Thalestris24]

The wavelength of the cosmic microwave background corresponds to a 3 deg K black body. Where space is empty it can't itself have a temperature. Heat is the kinetic energy of atoms and molecules - no atoms/molecules means no heat. Where there are atoms/molecules/dust/planets etc. they can have kinetic energy so can have a temperature.

[Alien 13]

I think i confused myself relating a temp measurement to microwave energy rather than watts/square metre. 

Alan

[Thalestris24]

I think it's a hard thing to get your head around because it's outside our everyday experience! Of course the coldest temperature an object in space can get is 2.7K because of the cosmic microwave background which is everywhere.