If space is a vacuum, how is the temperature in space on average °2.7 Kelvin and not °0 Kelvin?
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It’s not a complete vacuum, there’s still the random particle out there and they have energy.
Because space is NOT a vacuum.
Most of the matter is attracted to various gravity-producing bodies, but it’s not a true vacuum and as such will not have a complete absence of heat energy.
First, just like absolute zero is impossible to get to, space isn’t a perfect vacuum. That 2.7K number is calculated and has more to do with the flux of light and other particles through the vacuum than how we traditionally think of temperature.
Space is not a perfect vacuum there are atoms everywhere, even in intergalactic space we talk about 10 atoms per cubic meter. Vaccum often just mean significantly lower pressure then atmospheric pressure on earth.
There is no degrees in Kelvin so it is 2.7 Kelvin, not °2.7 Kelvin. It refers to one single thing the Cosmic microwave background. That is the temperature of an object that emits the same spectrum of black body radiation as the Cosmic microwave background. So if you place an object between galaxies that it the temperature it will reach. The temperature drops until the incoming radiation is equal to the emitted radation.
Space does not need to be cold, it can be very hot. The warmest part of earth atmosphere is the Thermosphere which is 80-600km up. The pressure is so low we call it vacuum this is where ISS orbits earth. The temperature of the gas here can reach 2500C. But up the number of atoms and therefore the amount of energy per unit of volume is very low.
So incoming energy from the sun and radiate energy out to space is the major factor in determining the temperature of an object, the very thin atmosphere have a minuscule effect. If you are in direct sunlight you will be warmed then if you are on the surface of the earth, the sunlight is stronger because there is no atmosphere to reduce the intensity, there is also not air around you that can cool you down. If you are in shadow it is quite cols. So for ISS the sunny side can be 120C and the shades side -157C at the same time.
The solar corona which is a thing plasma around the sun can have a temperature in excess of 1 000 000 kelvin. That is at pressure we consider vacuum.
So there is not any perfect vacuum the 2.7K is the black body temperature of the Cosmic microwave background. The temperature you have in space will primarily be determined by where you are relative to other objects like the sun. The temperature of the thin gas around and the Cosmic microwave background do not have a huge effect if you are as close to the sun as Earth is.
A perfect vacuum has no temperature. It’s not zero degrees or otherwise. It’s a zero divided by zero error.
That said, there absolutely is (a tiny bit of) matter in space, and if we treat space as a photon gas then that has temperature too, with heat coming from sunlight.
Space is a near vacuum it is not a total vacuum there are occasional hydrogen atoms wandering around along with cosmic rays and other energy.
While there are random particles floating around space, the temperature of space being 2.7 Kelvin is literally space glowing in heat leftover from the big bang. This heat is felt as radiation – specifically microwave radiation – which are photons just like infrared light or visible light. These photons have no problem traveling through a vacuum… and the ones we’re talking about have been traveling for almost 14 billion years.
the temperature relates to the leftover temperature from the big bang, and it’s the flood of electromagnetic radiation that permeates all of space. this is photons that are still filling all of space and preventing anything in from cooling to absolute zero. (although it’s not possible to get absolute zero in reality, it can get closer than 2.7K)
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