The sun warms up our planet but space is cold. If I lit a candle and stood 20 feet away, I could see the light but not feel the warmth. So, why do we feel warmth from the sun but space isn’t warmed by it?
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Heat is an interesting thing.
To understand heat, you have to understand what it is – and I find that a great example to use (and follow me here), is imagine you have an atom, but even more relatable; imagine an atom is a little bee that you put inside of a little ball. Now imagine that he’s in the center of a bunch of other bees that are also in their own little balls.
Now imagine you, as the sun, come on in and shake the little ball – the bee gets angry, and starts bzzing quite rapidly. Depending on how much he bzzes and shakes his little ball, the bees next to him will start bzzing, and depending on how much they bzz, the bees next to them will buzz and so on and so forth. What this represents is you putting energy into atoms – which the sun does with light.
When those atoms are next to each other, then their “excitement” and movement, can cause other atoms to also start moving around. Now looking back at the bees, your first bee is going to bzz the most, but the bees around him are probably going to bzz less, and the bees around those ones are going to bzz less. Just because you lose some of the “excitement” of the bees every layer you go down.
Some of the commotion you generated is going to be lost, because that energy has to used to move around and bees get tired. So eventually it tapers off. How well these bees – or atoms rather – can actually spread their buzzing around is a property of elements and materials that we measure.
So for instance, metals like Iron – are great at getting hot really quickly; this is why sticking metal spoons in a very hot dish is not a good idea. The bees that make up the spoon that are in the pot, with the energy will start bzzing fast, and the bees that make up iron are pro athletes at bzzing and don’t too tired, so they’re not losing much of that energy. So the spoon gets reaaalllly hot because most of the bees on the end of the spoon that you’re touching are also bzzing pretty hard.
Now that we’ve established that this concept of heat is actually just atoms buzzing around with energy – then space makes a bit more sense. Remember that space doesn’t have an atmosphere or any atoms around. It’s just empty. So there’s no bees to bzz and so no heat just around. UNLESS you’re getting directly hit by the sun.
The sun is a giant nuclear reactor – and it makes a looooot of energy. If you had an asteroid that was facing the sun in space, it would actually get incredibly hot, because all of those bees in that asteroid are being hit with the same level of shaking by the sun. That’s what happens with the moon, on the side that faces the sun – the dirt can get as hot as 260 F.
Now Earth’s atmosphere, might look empty, but remember that it’s actually full of stuff. We basically live in a soup of atoms; and those atoms are just like the bees. When the sun hits the bees with energy at the tippy top of our atmosphere, they start buzzing around and that buzzes around until you on the ground feel *warmth*. Now you feel warm and not burning, because the atmosphere atoms – or bees- around you are 1) not the ones being directly shaken by the sun; those are the ones sitting at the very edge of Earth and 2) just good enough at spreading the bzzing that you’re warm, but not so good that you’re on fire.
Going back to your question, this is why the candle doesn’t feel super hot either. We measure energy emitted over time – or how hard you shake the bee – in watts; we call it power!
A candle only generates about 80-100 W in power. So the bees in the atmosphere aren’t great at spreading that around. If you stuck a metal spoon on the candle though, you could easily feel that. Now they can if the candle becomes a fire of course, and that’s why we make a fire for warmth on cold nights. But remember that the bees are actually used to dealing with the sun – which makes around 44,000,000,000,000,000 W in power.
Hope my answer was helpful!
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