I see a lot of videos and shows where, if a person gets thrown out of an airlock, they immediately freeze to death. Disregarding the usual Hollywood exarcebation, WHY is space “cold” if the Sun generates so much heat radiation that it warms our very planet every day? Shouldn’t space be “warm”, then?
In: Physics
Here on earth, we have a lot of atmosphere between us and the sun’s rays. So the sun only warms us directly a little, most of the warmth we feel is from the air warmed around us.
In space, there is no air. Which means there is no air to warm us, and no air to shield us from direct light. This means that if you’re in the shade, it’s incredibly cold as there is no air around us to retain some of that heat. Similarly, if you’re in the direct light of the sun, it’s incredibly hot as all the energy that would have been absorbed by many layers of atmosphere is instead absorbed entirely by you.
If you were an astronaut in a spacesuit, facing the sun, your front side is going to be extremely hot, and your back side in the shade would be extremely cold. If you were not in the spacesuit, your front would cook even while your back froze.
There’s no atmosphere to blow air around and heat everything evenly. So the side facing the sun would burn while the other side freezes.
Space is a vacuum .. because space is a vacuum, there are nothing to convect heat from the sun,
Just to note: those movie things where a person goes into space and freezes instantly are absolute cobblers. Even in the shade (which, as mentioned in other posts, *is* very cold) the only way you can lose heat in space is via radiation, since there’s no atmosphere to convect heat away, and radiation is a very slow process, especially at the sort of temperatures a human body is at. It would take hours in reality for you to freeze if you were in space–the more immediate lack of oxygen causing you to suffocate would be your primary problem.
One of the ways heat is transferred is by particles interacting. Hotter particles travel faster and transmit more energy = more heat. This is why you can be in a 100°C sauna for a couple of minutes, but if you put your hand in a 100°C pot of water you get burned instantly: there’s simply less particles to interact with and transfer that 100°. Since space is a vacuum, there are no particles to interact with and therefore no heat. And to go full ELI5: because cold is the absence of heat, space is cold.
The side of you that is in the sunlight could get pretty hot, depending on your proximity to the sun/a star. Mercury has no atmosphere and is over 400°C on the surface so you’d at least freeze while get pretty crispy on one side at that priximity. The surface of the moons of Mars stay beneath freezing temp even in full sunlight, so it’s power diminishes fairly quickly.
Warm and cold don’t really make sense in a vacuum like space
There aren’t many particles so the average kinetic energy of a given volume is extremely low so space is extremely cold, but since there aren’t many particles you won’t conduct heat away almost at all, it’ll have to slowly radiate away from you
The sun meanwhile is blasting a ton of light at you which will heat you up if you don’t reflect it away. This is why most things in space are white or reflective because overheating in space is a much bigger problem than freezing
If you were shoved out an airlock with a little oxygen mask so you didn’t immediately suffocate and die, you would end up overheating quite quickly(even if you weren’t in direct sunlight) because your body is a 100W heater and without air to conduct the excess heat away to you’ll begin to get warmer and warmer until you overheat and die.
Most of an astronauts spacesuit is insulation to protect them from the sun’s heat, and water cooling to keep them safe from their own body’s heat
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