| Do you think space, or rather the vacuum, is | | | | warm ground radiates off and partially through |
| cold? During my survey on the web during the | | | | convection heat exchange between air and |
| past few months, it clearly showed that most | | | | ground material molecules and part by what it |
| people would answer yes to that question. Fact is | | | | absorbs itself directly. The same principle is valid |
| that only matter can have a temperature, which | | | | for glass and that's why your car gets so hot |
| is the speed of its molecules... | | | | inside, when it is parked in the sun. Likewise the |
| Do you think space, or rather the vacuum, is | | | | temperature in green houses rise above |
| cold? During my survey on the web during the | | | | surrounding air temperatures, as is the purpose of |
| past few months, it clearly showed that most | | | | those. |
| people would answer yes to that question. | | | | The warm atmosphere of the Earth radiates off |
| Fact is that only matter can have a temperature, | | | | heat into space at a far lower frequency than |
| which is the speed of its molecules. The faster | | | | what it received from the Sun and this heat |
| the molecules in a material move, the warmer | | | | disperses into space, without "warming" it up. |
| that material is. Per definition, an absolute vacuum | | | | Space, the vacuum, cannot have a temperature |
| is a void, nothingness and therefore it cannot | | | | and so the heat energy that the Earth's |
| have any temperature. In as far as the space of | | | | atmosphere radiates off, disperses into larger and |
| the Universe is an absolute vacuum, that space | | | | larger volumes of "nothingness". The Earth is thus |
| cannot have any temperature and it is thus not | | | | not cooled by any "cold" space, because that |
| "cold". | | | | would require convection, which the vacuum |
| However, an absolute vacuum does not really | | | | cannot provide. |
| exist; there are molecules whirling around | | | | Likewise, the distant planets are very cold, |
| everywhere in space. Actually, some recent | | | | because they receive very little energy from the |
| theories say that all these molecules whirling | | | | Sun, not because they are surrounded by "cold" |
| around, constitute more mass than all the visible | | | | space. Any object in "dark" space, not receiving |
| galaxies contain together - it's called "dark matter". | | | | any heat, nor generating any itself, will become |
| Even so, the density of these molecules is so | | | | extremely cold, as it radiates off whatever little it |
| incredibly low, that in practical terms, as far as | | | | still has. How cold, we'll see at the end of this |
| space technology is concerned, interplanetary | | | | article. |
| space behaves as an absolute vacuum. Even the | | | | The average temperature of the Earth is |
| Moon, that actually does have an atmosphere in | | | | determined by a balance between received and |
| the sense that the density of its gas molecules is | | | | given off heat energy. The atmosphere's |
| considerably higher than in "free" space, can yet | | | | temperature stabilizes there where both amounts |
| be seen as an absolute vacuum environment in | | | | are the same. Hence, the Earth gives off as much |
| practical terms for human activity there. This | | | | energy as it receives from the Sun; nothing is |
| means that the molecules that are there, do not | | | | "consumed", or "used" as many erroneously think. |
| have a measurable contact (convection) heat | | | | The same is valid for a green-house and you car |
| exchange effect with other materials around and | | | | parked in the sun; the inner temperature stabilizes |
| thus a Moon vehicle or base on the Moon can | | | | at a value where energy balance is reached. |
| neither be cooled, nor heated by these molecules. | | | | Of course, not all the solar energy that hits the |
| The same is valid for space vehicles traveling | | | | Earth is absorbed by it. Much of it is reflected |
| around in the Solar System; they also have no | | | | back into space. From the rest, the atmosphere |
| measurable heat exchange with the molecules | | | | absorbs a part itself and lets through a part to |
| moving in the vacuum around. | | | | reach the surface. As long as the properties of |
| Even on Mars, that has a well defined | | | | the atmosphere do not change, the Earth's global |
| atmosphere, such heat exchange effects would | | | | temperature will not change, but if we bring about |
| not have much significance for human activity | | | | noticeable changes with our emissions of |
| there, though it would be noticeable nonetheless. | | | | whatever gases, anything can happen. The Earth |
| Surely, the air temperature on Mars can locally | | | | can become cooler or warmer. Today the talk is |
| come up to plus 30 degr. C, but that doesn't | | | | about global warming, but there are scientists who |
| mean you would "feel" it, the same as on Earth, | | | | argue for a risk of global cooling also. In the end, |
| because the Mars air is so much thinner. The | | | | nobody knows for sure, because the heat |
| atmospheric pressure on Mars is just 6 mbar, | | | | household of the atmosphere is a very |
| compared to Earth's atmospheric pressure of | | | | complicated system, with many unknown |
| 1000 mbar. No industrial "vacuum" pump on Earth | | | | parameters. |
| could reach such a low pressure and it is yet | | | | However, if it ever would happen that we release |
| called a vacuum pump. Hence, in technical terms, | | | | so much heat from fuels, that it becomes a |
| also Mars could be seen as a vacuum | | | | noticeable part of the Earth's total energy |
| environment for astronauts, just not an absolute | | | | household, we would indeed warm up Earth by it. |
| one, as it is on the Moon. | | | | I don't think that ever will happen, it's just a |
| This all means that space, the vacuum, is a | | | | theoretical exercise, but we do cause |
| perfect temperature insulator for convection heat. | | | | heat-pollution locally, warming up waters around |
| The only heat exchange that can be done | | | | large power plants that are cooled by them and it |
| between bodies in the vacuum is through | | | | affects the biological systems there. |
| radiation, because the vacuum lets | | | | On Earth, cars, green-houses and whatever other |
| electromagnetic energy pass through. Very | | | | structures, are heavily cooled by the surrounding |
| fortunate, so we can get light and warmth from | | | | air, especially if there is wind blowing around them. |
| the Sun, all being electromagnetic radiation. The | | | | Not so on the Moon for example. If you see |
| frequency of this radiation is a measure for how | | | | science-fiction designs of huge glass cupolas on |
| much energy it transmits. The higher the | | | | the Moon and space-crafts with large glass |
| frequency, the more powerful the radiation is and | | | | windows all around, you are basically looking at |
| usually penetrates deeper into materials. X-rays | | | | ovens. If exposed to sunlight, they would |
| have a very high frequency and are therefore | | | | self-destruct by overheat, unless practically all of |
| powerful enough to penetrate our bodies, which | | | | the solar heat is reflected (not absorbed !) by |
| for example is used in medical applications. | | | | such glass, or whatever transparent material. |
| Gamma rays are even more powerful and are | | | | Even then, such habitats are additionally heated by |
| generated by decaying atoms - nuclear radiation. | | | | the body heat of people in there and by the |
| Heat radiation is called infra-red, because the color | | | | power supplies to run technical systems (all |
| red is the lower frequency limit of what our eyes | | | | energy decays to heat at ambient temperature - |
| can see (violet the upper). | | | | Second Law of Thermo). All that heat must be |
| Infra-red has a too low frequency for our eyes | | | | radiated off also. |
| to see and we feel it as heat instead. Its | | | | How cold can an object in "dark" space become? |
| frequency relates to the temperature of the | | | | Many say 3 Kelvin, which is the "temperature" of |
| emitting body, the higher the frequency, the | | | | the cosmic background radiation (actually 2.7 K). |
| warmer that body is. This causes the so called | | | | This radiation is assumed to be a remnant of the |
| green-house effect, because certain materials are | | | | Big-Bang and its frequency corresponds with 3 |
| more transparent for higher than for lower | | | | Kelvin. Many think erroneously that this is the |
| frequencies. The surface temperature of the Sun | | | | temperature of space, but that is of course not |
| is 6000 Kelvin and the according frequency can | | | | true. An object in deep, deep dark space can |
| penetrate the Earth's atmosphere. As it hits the | | | | become colder than 3 Kelvin, but the Second Law |
| ground, most of it gets absorbed and warms up | | | | of Thermo says it can never become 0 Kelvin, |
| the ground material - ever noticed how hot beach | | | | because 0 Kelvin is not a temperature - it is the |
| sand can be? | | | | absence of it, "nothingness", a void. Matter as we |
| However, the thus generated temperatures are | | | | know it, cannot exist at 0 Kelvin, |
| much lower (fortunately) than that of the Sun | | | | However, this is not agreed upon by all scientist. |
| and the Earth's atmosphere is not transparent for | | | | Look for the "Third Law of Thermodynamics" in a |
| the according lower frequencies and so it warms | | | | search engine and you will find it - I personally do |
| up, partially by absorbing the energy that the | | | | not agree with that "law". |