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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The reason you feel warm right now is because you are surrounded by air, which is radiating its stored heat from the sun into you from all sides. In space there is no air around you to radiate heat or damper the sun’s direct energy, you would burn on one side that is lit by the sun’s light and freeze on the other side that is in the shadow. Speaking of shadows in space, because there is no air to bounce light rays around in space, astronauts have described putting their hand in a shadow (behind the spaceship) and it going completely black like staring into a void.
If you account for the history of the universe, after the big bang the universe was very hot, like a plasma. As it cooled and the universe formed there was a Goldilocks period for a few hundred millions years where space was at a habitable temperature. Other than having no air to breathe you could have floated in space and felt completely comfortable.
simply put there is nothing to be hot or cold. heat is really just the movement of atoms in an object. the faster they move, the hotter the thing is. space, while not a perfect vacuum, is for all intents and purposes empty, so there are no atoms to be hot or cold
edit: i guess, since cold is just the absence of heat, space is cold because there is no hot
What is heat? It is the energy of particles vibrating. When something is hot the particles are vibrating fast, when something is cold the particles are vibrating slow (or standing still if it is 0 kelvin).
So what is empty space? No particles, so is space hot or cold? Neither, there are no particles so you can’t say if they are fast or slow as they just aren’t there. Therefore space has no temperature. (what speed does a car that doesn’t exist have? None, there is no speed as there is no car)
The idea that space is cold is kind of wrong, I mean it’s less wrong than saying it’s warm as space does not contain any thermal energy but saying it has no temperature is more correct.
The way something heats up is particles hitting particles so that they start vibrating, either because the particles are close to each other (your hand touching a hot thing) or by particles emitted (infrared for example) by that source of heat that can travel and hit something to make it vibrate. (you sitting 5 ft. from a fire, still feeling it’s heat but not touching it)
The sun emits photons that can hit particles and make them move. However space is no particles at all so the photons move through the space without hitting anything so the particles don’t “hit” space. (which means they don’t lose any speed or energy) Once the particles reach the earth they start hitting particles and making them move, and thus they start to heat up whatever they hit on earth.
In practice the space in between earth and the sun isn’t completely empty but if a few photons hit some stray atoms on the way to earth there is still more than enough energy left.
Also, if you would be more sensitive, you would feel the candle from 20ft. away as that candle is emitting some infrared too, just not enough to be noticeable by a human.
In theory if you would probably feel more of its heat if there was no air in between you and the candle as the particles traveling from the candle to you wouldn’t be bumping into all of the air first and lose most of their energy.
Space does not have temperature in the classical sense. Things get hot, like air or water or rocks. There is nothing in space to get hot or cold.
The notion that space is cold is misleading, should you find yourself in full view of the sun in space, you’d get very hot and die.
In shade, not so much, but cooling equipment in space is quite a problem. For the same reason coffee remains hot in a thermos.
If you found yourself in shade in space, you’d freeze, but it would take a while.
Temperature is a measurement of the amount of energy in matter. It’s directly related to the movement or vibration of atoms.
When you heat something you input energy into it and as a result the atoms will move/vibrate faster and faster.
When you cool something you take energy out and as a result the atoms move around less. At the lowest possible temperature, absolute zero, the atoms don’t move around at all anymore. That’s why it’s the lowest temperature, you can’t take any energy out anymore, there’s already no more movement.
Space is vacuum. Since it’s not matter, it can’t have temperature.
Matter in space can have temperature, such as gas clouds, asteroids , spacecraft etc. But space itself is nothing.
In space, you only get heated by the direct incident radiative energy from the sun on the side facing the sun, and depending on how far away from the sun you are, that may or may not be enough to overcome the heat loss you radiate to mostly empty space. Things that are closer to the sun might get extremely hot on that side, but things farther from the sun may be only slightly warmed.
On the side away from the sun, it gets very cold very fast, and there is no atmosphere to help carry the sun’s heat to the other side as happens on planets with an atmosphere. You could rotate to even out the incident radiation, or fly a reflective surface on the “away side” to reflect solar heat back onto you. But managing the heat differential is a big issue for spacecraft and satellites.
You may notice something close to this effect in higher altitude deserts, where the days can get very hot and the nights very cold.
A lot of other commenters have pointed out that there’s a misunderstanding of what we mean by “hot” when there’s nothing to heat up. But, it might interest you to know that while space is effectively empty compared to the earth (10^24 atoms/cm3) and its atmosphere (10^21 atoms/cm3), it’s not literally empty. There are still particles around in the solar system (5-40 atoms/cm3), and continuing downward as you leave the galaxy (10^-3 atoms/cm3).
These particles, however few they are, actually are quite hot (according to the physics definition, which is that temperature = average speed of particles), and astronomers can generally show they can be anywhere from 10^4 to 10^7 K — much hotter than air is on Earth! It gets heated up by stars and gravitational acceleration, and cools quite slowly.
It doesn’t feel hot when you’re there, because only a few particles even hit you per second, but each one will slightly heat you up! You’re just so complex chemically that it’s much easier for you to cool back down by radiation than it is for the particles, so they would never heat you up to their average temperature, no matter how long you waited.
Because there is nothing in space to be warmed by the sun. What we perceive as temperature is vibrating molecules that bump into us. When we feel warm in the sun some of that is the photons from the sun whose energy is absorbed by the molecules in our skin which then causes them to vibrate, but mostly what we feel is the vibrations of the molecules in of air which absorb energy from the sun and then bump into us, passing that energy along. Objects in space that are near enough to a star receive energy in the same way, but there are no molecules in space (or at least extremely few) to absorb that energy and then pass it on to something else by bumping into it.
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