if everything that is surrounding us and everything else (the sun, other stars, planets etc) is cold to the point of beeing at absolute zero, how can things be at such a higher temperature? how can, for example, a spaceship keep a confortable temperature in the inside if outside there is such a massive temperature drop?
sorry for the many questions, but they all are part of the same big one 😀
In: 10
Vacuum is a great insulator.
It’s less that the universe is at absolute zero, and more that there is nothing to facilitate the transfer of heat energy. Space isn’t cold, it’s nothing, you can’t touch it.
Now the suns rays travel through space, pretty much uninterrupted and hit the earth heating it up. A good amount of that heat should be reflected back out into space.
Global warming is a build up of material in the atmosphere that is holding onto that heat and not letting it escape. A good example is being in a car on a hot day. The greenhouse gases are the car windows, they let the light in but keep the heat from getting out.
It’s not absolute zero, but I get your point.
It’s a question of mass.
There’s three ways to transfer heat.
There’s conduction, where two things are transferring heat by physically touching each other. This is the fastest way of transferring heat. For example, an electric stove heating element is physically touching the pot.
There’s convection, where two things are transferring heat by physically touching a medium that moves between them. For example, if you’re baking something in your oven the heating elements are heating up the air which circulates inside the oven where the air touches your food and heat it up. This isn’t quite as fast as conduction, but it’s still pretty good.
The last is radiation. Every object releases light based on its temperature (this is called black body radiation and it’s how infrared thermometers work and how we can tell what temperature stars are). This is not a very efficient method of heat dispersion, and it gets less efficient the larger an object is because the ratio of mass to surface area results in a smaller and smaller percent of the energy being able to radiate out because the surface area is smaller compared to the mass.
So to bring this back to your question: There’s no stuff in space, relatively speaking. There’s only a couple of *atoms* per cubic meter in deep space. No stuff means no conduction or convection, or at least not enough to matter. That leaves radiation. Which is how the sun heats the earth.
>how can, for example, a spaceship keep a confortable temperature in the inside if outside there is such a massive temperature drop?
Fun fact: We have to use heaters! Spaceships are designed to radiate out more heat than the stuff inside generates (people and equipment) and the supplement that heat loss with heaters. We do this because vacuum is an incredible insulator for the reasons stated above (the best insulated cups and coolers, like Yeti, are insulated by nothing at all – by vacuum.) so it’s safer to run cold because if you ran hot you’d cook everything inside.
If you have a bonfire inside a bedroom, the average temperature of the bedroom is quite high. If you have the same bonfire in a stadium, the average temperature of the stadium is much lower, because there is a much higher amount of non-bonfire (proportionally). In space, there is insanely a looot more non-bonfire (temperature of the void is absolute zero, to simplify it), so even if there are things as hot as stars, the average temperature is very low. However, vacuum is also not a good heat conductor: no direct contact or convection, so the only way to transmit heat is radiation, which for something with the temperature of a spaceship is a very slow process. But for something the temperature of a star, the amount of heat transmitted is much higher, therefore the Sun heats the Earth.
Two main reasons. The first is that a vacuum makes for an extremely effective insulator. The near nothingness in outer space makes it hard for thermal energy (i.e., heat) to radiate away quickly. It still does, but it takes a long time. The second reason is that stars (and even planets) produce their own heat – stars through nuclear fusion and planets through radioactivity (and they have lots of residual heat from formation and are heated by the energy from their stars too). Regarding spaceships – they are well insulated.
On Earth, where we are surrounded by air or water, distribution of heat happens easily as molecules of some hot thing come into contact with lots of air or water molecules constantly, allowing transfer of kinetic energy from the more energetic thing (the hot thing) to the less energetic air or water. Even so, isolated air is a pretty effective insulator too as long as it’s unable to mix with the air all around us. It’s how most insulation (everything from fiberglass to feathers) work – they trap the air keeping it from mixing with the atmosphere.
The initial energy comes from work done by the gravitational field. Widely separated particles fall towards each other, and when they finally collide their kinetic energy becomes heat. Every part of a star initially falls on top of the rest, increasing the strength of the field, so it has a snowball effect. Eventually it contracts under its own weight enough to start a nuclear reaction.
The temperature of space is misleading. Yes, it is only ~3 Kelvin, but it is also incredibly little matter there. We are talking about as little as one atom per cubic meter for most of space. That’s an absurdly huge factor off from matter on a planet. Near a planet, the amount of matter is a bit higher by a meagre factor of less than 10 million.
Altogether, there is 10^^21 to 10^^24 as much matter per volume here on Earth than there is in space near us, and an even larger factor for deep space. Heat _capacity_ depends on how much there is, twice as much matter stores twice the cold/heat. his means **a single 1 meter cube of Earth stores as much thermal energy as a 10,000 kilometers sized cube of near-Earth space!**
So it needs quite a lot of that space to cool the planet, if we would give our warmth to it. In reality, this extreme lack of matter isolates the planet very well. Almost all heat we lose is actually due to thermal radiation. But that amount is matched by the much stronger thermal radiation from the sun, luckily restricted to small area of the day sky.
And even minor changes in radiation off from Earth or from the sun has devastating consequences. The effect of temperature is relative to the absolute numbers: if we are, say, at 300 Kelvin (~27° C) now, then a 1% increase of solar radiation, or a 1% decrease of our thermal loss, means a temperature change of ~3 K = 3° C. That is already significantly more than we are currently dealing with and quite a nightmare for life on Earth; humans included.
Stars, like the sun, are definitely not cold or surrounded by cold.
Space in general is cold because most of it is empty, but things in space are only cold when they don’t have a source of heat.
You would actually have to deal with a lot of heat if you left earth and got direct sunlight without earth’s atmosphere to protect you like it does here and with no air for you to radiate your heat away.
Anyway, to answer your question; the sun and other stars get to be very hot because they are massive fusion reactors that release tons of energy. They are their own heat source.
Planets also have some heat of their own. From my understanding, planets like earth are rocky with a molten core; however, that isn’t what makes earth warm for us, that molten core’s heat sometimes heats up some areas in deep oceans, but it rarely makes it to the surface where we live.
Most of our warmth comes from proximity to the sun.
The reason earth has a nice temperature is our atmosphere. We have a greenhouse effect going on. Some gases in our atmosphere, like CO2, are good at limiting how much heat and UV lights from the sun comes in, but also how much can leave.
It means it doesn’t let all of the sun’s warmth in to cook us alive during the day, but that what gets inside stays inside for longer so we don’t freeze at night.
This is why climate change is such a scary thing to mess up like we did. We have too much of these greenhouse gases building up faster than ever before, and we are holding onto more heat, which increases the global temperature and causas all sorts of problems that stack up over time.
Who knew space was the ultimate cold shoulder?
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