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When you step outside during the day and feel the sunlight on your face or body, it’ll feel warmer. But if you go back inside or somewhere with a shade, it could suddenly feel a lot cooler. This happened even if the sun is still right up there in the sky as it has always been. Now, realizing this scenario, some people ask, if the sun is in space blasting energy and its sunlight in all directions, why isn’t space warm?
The space between planets and the sun is cold, but in our case, Earth gets warm when the sunlight reaches us, so why exactly are those vacuum gaps cold? What is the explanation behind it? Let’s find out.
Why the Sun Feels Hot, But Space Stays (Mostly) Cold
On Earth, there are two main ways you could feel the warmth of the sun. First is through conduction and convection, where the air gets warmed, touches your skin, and then moves around. The other is through radiation, where the light and infrared rays of the sun are directly absorbed in your body.
So, in space, these two ways are not applicable to heat up the vacuum gap. There is no air, no wind, and only a few little particles spread out per cubic centimeter in many different regions. In other words, there is nothing like the Earth’s atmosphere that would be able to hold the heat.
Moreover, the sun still sends radiation and its visible lights and other electromagnetic energy, which is why the satellites and space stations up there get warm fast when they get hit by the rays. But, space itself does not have much to warm, and since heat is just energy in particles, and there are almost no particles, then there’s almost nothing to be warm.
Read more: Space.com
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How Can Space Be “Cold” If Some Parts Are Millions of Degrees?
Temperature is the measure of the average energy per particle, but how hot something feels could be different than that. It will also depend on how many of those particles that are hot are hitting you and warming you up. In a dense gas, just like in a regular sauna, there is a lot of air and particles that can transfer the energy to you quickly, making it feel hot.
However, in certain regions of space, some particles may have high energy but be very few in number. So, even if some of them hit you, it might still feel cold. That’s why an astronaut in orbit could both feel the heat from the radiation of the sun and could also get very cold if away from it quickly due to their body radiating that heat. There is no air to smooth out the temperature differences and act as an insulator.
Author's Final Thoughts
The sun is burning hot, but space still feels cold for a simple reason. Because heat must be stored in matter, and space hardly has any. The sun’s energy projects in all directions around it, but it can only turn into noticeable warmth when it hits and is absorbed by something, such as the surface of the planet, air, satellites, or your skin.
Read next: Did Earth’s Magnetic North Pole Move? — Here’s What Scientists Have Discovered
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