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