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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Because space is empty. Heat as we experience it can only be applied to physical objects that conduct their heat into you. Of course, if you were naked in space, you would feel the heat of the sun, but only directly from the sun. If you faced the sun, you’d die, but your back wouldn’t be getting any heat.
It is and isn’t, it’s as extreme as you are imagining.
The difference between “sun” and “shade” for the ISS is roughly *500 degrees F.*
So if you’re just floating in a space suit and facing the sun, the sun-side of your suit is 250F, behind you the dark side of your suit is -250F.
The essence of your confusion is space is empty and “having a temperature” implies you have an *object that is warm.* Since space is, be definition, the absence of an object, it can’t be warm because there is nothing there to ‘make warm’ in the first place (unless it’s you in your space suit).
This goes back to middle-school science class but heat travels from object to object in a few different ways but two main ones involve physical contact between objects, since you’re not touching the sun or the candle, that’s not what’s happening here. The third way is through radiation, energy zipping through the air as light. Both the sun and the candle are bright because they are giving off light radiation and that will warm you if it touches you. Of course a tiny candle doesn’t “feel warm” the same way the sun does on a bright spring morning but that’s mainly an issue of scale, a tiny little flame vs. a celestial object.
You can’t warm nothing and space is a whole lot of nothing.
It’s the same reason hydroflasks work so well, they put a vacuum between the inner and outer walls and vacuums don’t allow much if any heat transfer
Because space is nothing. What is warm on earth is the air. Or any object / particle. There is no air in space. Nothing to be hot out there
Heat is thermal energy transferred between systems due to a temperature difference.
Thermal energy is kinetic energy of atoms vibrating and colliding in a substance.
Space is the absence of atoms! So there is nothing to vibrate.
“Hot” is a word we use to describe what it feels like when atoms/molecules are moving around a lot. In space, there are basically no atom/molecules *to* move around.
In other words, heat is a characteristic of matter, of “stuff”. Space is not matter, it’s a whole lot of “no stuff”.
The sun warms stuff up when its light hits the stuff. But empty space has no stuff to get hit by the light.
“heat” is the energy of moving molecules. more movement means more heat, less movement means less heat. no movement means “absolute zero” (-273 C, or 0 K). since space has nothing in it, there are no molecules to move. the biggest danger to human skin isn’t the temperature, it’s the various radiation coming off the nearby star… with scuba gear and SPF 9000, you could conceivably survive out there naked (don’t touch the metal, tho… that radiation may cause it to be hot enough to give you burns! also, metals may get vacuum-welded together)
Other people have answered so I’d just like to add: you do experience the warmth from a candle 20 feet away. It is a small amount of heat but still measurable.
If you put your hand directly over the candle you will feel the hot air on your hand and yes, of course you are not feeling this heat (directly) from 20 feet away. Instead you feel the thermal radiation (think invisible light being beamed at you from the candle). If you’ve ever been near a bonfire you will certainly know this experience: it is a heat that makes your skin feel dry, and covering your face with a hand will shield you from it since you’re blocking the radiation.
because ‘stuff’ is what we feel warmth from, and that includes air.
You feel ‘warm air’ because the molecules of the air are excited and transferring that energy to you, or your energy is radiating off to them.
space just doesn’t have any of that stuff to be ‘hot’. There’s practically no molecules to get excited.
It also kinda works in reverse. cooling off in space is difficult because there aren’t other molecules to ‘take’ your energy.
The idea of empty or nothing is hard to grasp. The sun warms the air, and objects on earth, in space there’s nothing to warm
The heat from the sun is kinda like walking around a mall with no people trying to give away free balloons. Then you find a shop called earth with a bunch of people in it to take your balloons
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