1. Trajan

    Trajan New Member

    Hey Guys
    I'm new to this discussion board.
    for the past couple of months, I have been looking over these silly Flat earth claims, [like]

    "the melting points of the metals used in satellites are far lower than the temperature in the "thermosphere" where satellites supposedly are."
    - Eric Dubay

    I have been trying to check this whole thermosphere thing. I hear some say that things don't get very hot when in the thermosphere because there are very little gas particles to allow for convection and conduction but their is still radiation, which is able to heats things up in a vacuum.

    Is Dubay inaccurate when he claims that the thermosphere should be able to melt the satellites? And how can our satellites and other space craft survive the thermosphere?
    Last edited by a moderator: Sep 2, 2017
  2. Mick West

    Mick West Administrator Staff Member

    Radiation also cools things down. Any object that is heated up will radiate that heat away, the hotter it gets the more heat it radiates per second. So as the Sun's input is constant, eventually the object will reach a temperature at which it is radiating the same amount of heat as it is absorbing. This is known as the "radiative equilibrium temperature". Part of satellite design is in minimizing the absorbed radiation, and maximizing the radiated radiation. There's whole books on the topic.

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  3. Trajan

    Trajan New Member

    Thanks Mick for your response.
    So just for clarifacation, when an object absorbs radiation heat, it radiates the same amount to counter act this. Am I understanding this right?
  4. Mick West

    Mick West Administrator Staff Member

    When it gets to a certain temperature, yes. Consider, for example, the Earth. We are in full sun, but the planet does not continue to heat up, because it's radiating away energy into space.

    The actual physics can be quite complicated. There a difference between the incoming broad spectrum radiation of sunlight, and the outgoing infrared radiation.

    This pdf on the topic is slightly more accessible than the book. It has lots of images of the various heat management devices.

    Last edited: Nov 6, 2015
  5. Trailblazer

    Trailblazer Moderator Staff Member

    There is a fundamental difference between temperature and heat.

    Temperature is a measure of how much energy individual particles have.

    Heat is a measure of how much energy is contained by all the particles in a given volume.

    The thermosphere is a very low density gas (very few particles) so even though the individual particles have a lot of energy (high temperature), they don't hold much heat energy overall.

    An imperfect analogy - you couldn't stick your hand into water at 90ºC without sustaining serious injury. But you can sit in a sauna with an air temperature of 90ºC quite happily for quite a long period. The temperature is the same, but the amount of heat is very different.

    Satellites will still be heated up by radiation, of course, but this is quite easily countered by constructing them of reflective materials.

    A close relative of mine is something of an expert on satellites (including building them) so if you have any more specific questions I could try and get some authoritative answers.
  6. konkerinLion

    konkerinLion New Member

    How can the waste system for the clothes work on the ISS where they just let it go outside the ISS and get 'burned up in space' by the radiation, if radiation is cooling? Also why does NASA orion programme now need to probe the temperatures and see if it is safe for manned space travel when we are already there? Very confusing situation for young fathers to teach their children the truth. If you can clarify how this contradiction is that would be of great help. Otherwise our families will keep pondering for truth that makes logical sense. Because we are being told very different 'facts'

    All the best,

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  7. konkerinLion

    konkerinLion New Member

    Same question to you - how does the waste disposal systems work where the astronauts just throw their clothes out of the ship (theoretically speaking, obviously using a mechanical airlock device) and allow them to be burned up in space? Very interesting post thanks
  8. Trailspotter

    Trailspotter Senior Member

    After a new cargo is delivered to the ISS, the waste is loaded to the empty cargo ship that then is sent back to the Earth and burns in the atmosphere upon the re-entry.
  9. Mick West

    Mick West Administrator Staff Member

    Yes, the waste is burned up in atmospheric entry, which is pretty much the opposite of orbit
  10. Trailblazer

    Trailblazer Moderator Staff Member

    I think you are picturing a scenario where the waste spontaneously "burns up" once it is ejected into space?

    That's not what happens at all. Things only burn-up on re-entry, when they are falling extremely fast through the atmosphere. That's why space capsules,and the Shuttle etc, need heatproof tiles.

    I'm not sure what you mean by that. The heat testing for Orion is to do with its passage through the atmosphere, not in space.


    There are challenges for new manned spacecraft to do with space exposure, but those are to do with (ionising) radiation, not heat. The longest Apollo mission spent about 12 days in space. If we want to send men to Mars they will have to spend a year or more in space, so much more protection would be needed.
    Last edited: Nov 9, 2015
  11. Abishua

    Abishua Member

    This guy did an interesting experiment, he measured the difference of heating things up in atmosphere and vacuum..

    The results are as follows:

    using infrared 100w bulb
    Thermometer in atmosphere took 2min 25sec to raise the temp for 3 degrees C
    Thermometer in vacuum took 2min 20sec to raise the temp for 3 degrees C

    Then a different visible light bulb was used as a source of heat.

    result is:

    2:16 sec for atmosphere
    2:12 sec for vacuum

    so it actually heated up again more quickly in vacuum

    third experiment was heating a peace of plastic in atmosphere and vacuum.

    in both cases it reached the same temp of about 50 degrees C

    so in conclusion, are atmospheric molecules needed to transfer heat to solid objects in vacuum? since atmospheric molecules themselves are in vacuum that presents a question what would they use to transfer heat to themselves? If anything this experiment showed that the atmospheric molecules were actually "stealing" some of the heat from the solid objects and it took them longer to reach target temp.

    Any input on this? How do these results relate to satellites in thermosphere?

    if anyone is interested in more details here is the source video

    Last edited: Jan 1, 2017
  12. Hevach

    Hevach Senior Member

    The thermosphere is hot but rarified gas. Radiative heating from a light source like the sun or a light bulb is different than heat transfer from one medium to another.
  13. Z.W. Wolf

    Z.W. Wolf Active Member

    Before we do the work of answering your questions, I think it's reasonable for you to do the work of educating yourself in the basic issues involved. I think you should be able to answer these questions in your own words.

    1. What is kinetic energy?

    2. What is heat?

    3. What is the difference between heat and temperature?

    4. How is heat transferred?

    5. What is electromagnetic radiation?

    6. Do objects lose heat through radiation?
    Last edited: Jan 1, 2017
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  14. Mick West

    Mick West Administrator Staff Member

    Or more simply, what is the difference between heat transfer with:
    1. Conduction
    2. Radiation
    3. Convection
    The misunderstanding about heat in a vacuum are actually explained above. Unfortunately this is a actually a topic where you have to learn a tiny simple bit of physics to understand what is going on.
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  15. Trailblazer

    Trailblazer Moderator Staff Member

    A (perfect) vacuum has no temperature, by definition. Temperature is a measure of the average kinetic energy of the particles, and a vacuum has no particles at all.

    However, things surrounded by a vacuum can still gain and lose energy by radiation. If you are in space, which is very close to being a vacuum, then radiation heating is far more important than the tiny amount of energy you get from the "high temperature" (but very rarified) gas molecules.
  16. Abishua

    Abishua Member

    So if sun can heat up thermosphere to 2500C what is preventing it to heat up the more solid object like ISS to the same temp? It clearly is not vacuum.. because temperatures of plastic were taken after reintroducing atmosphere..
  17. Henk001

    Henk001 Active Member

    If I hold a needle for 10 seconds in a flame, it will reach a high temperature. If I heat up a kettle with a little water with the same flame, it will hardly rise in temperature after 10 seconds. Why? Because you need more heat (energy) to raise the temperature (the average kinetic energy) of the much more molecules of the kettle+water than you need for the few molecules that are in the needle.
    So the radiation flux of the sun (1,4 kW/m2) will easily heat up the few molecules that are behind every m2 when it reaches the thermosphere, but behind a m2 satellite there are a billion times more molecules to heat up. Apart from the fact that the satellite will reflect most of the incoming radiation.
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  18. Abishua

    Abishua Member

    Ok that makes sense, but eventually this flame does not go out after 10 minutes.. it's been heating up this "kettle" for over 15 years.. so I guess radiative cooling needs to cool this object as much as the sun warms it in order to keep equilibrium.. but the problem I have with this is.. if the surrounding temperature in a room is constant 20C, any object in that room will eventually reach that temp.. it will "balance out".. if its in vacuum it will do the same.. just takes more time, even though this experiment showed it takes less time.. I guess my problem is why does the ISS fail to balance out with its environment after this much time..

    When I bake something in the oven.. I can cover it with aluminum foil.. and it will take longer for food to reach the environment core temp.. but eventually it will..
  19. Auldy

    Auldy Senior Member

    The cake is a lot closer to the heat source though.

    And also enclosing it.

    That is not what is happening in the solar system.

    How close of an orbit to the sun would your al-foil covered cake have to be in order to be baked all the way through?
  20. Abishua

    Abishua Member

    well at 2400C it would bake really fast :)

    Its not just about how close it is to the heat source.. its also how powerfull the heat source is.. I guess the question is the balance of radiative cooling with constant sun warming.. if the cooling is slightly higher then in 15 years ISS would be a chunk of ice, if sun warming was slightly higher it would be in molten state.. The hard par for me to believe to be honest is that you can maintain perfect balance up there for such a long time..
  21. Henk001

    Henk001 Active Member

    The balance is not in temperature but in energy flux. If you loose the same amount of energy as you gain every second, then your temperature won't change (any more). If you put a dark object and a white (or shiny) object in the sunshine the black one will reach a higher temperature compared with the white one and both temperatures will also differ from the surrounding air.
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  22. Auldy

    Auldy Senior Member

    Mylar helps with the shielding bit.
    The station itself generates heat from the amount of machines running on it. It even has an air conditioning service to keep the inside cold - in space!
  23. Spectrar Ghost

    Spectrar Ghost Senior Member

    Radiative cooling increases as the station temperature increases, and decreases as the station temperature decreases. This negative feedback means that neither of the scenarios you describe are real possibilities.
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  24. Bruno D.

    Bruno D. Senior Member

    You keep thinking the ISS is a hollow chunk of aluminum that someone threw in the orbit.

    Do you really think that the balance is an accident and that there is no technology and thousands of hours of research involved? Did you know that keeping it warm is as challenging as it is to keep it cool?

    Have you researched how ISS is claimed to work? Example: https://science.nasa.gov/science-news/science-at-nasa/2001/ast21mar_1


    And last but not least, what's your source for 2400C as the temperature outside ISS?
  25. mm1145

    mm1145 Member

    a suggestion for you
    I was just re-reading "what if XKCD" one of the chapters there is on what might happen if a nuclear sub is transported to orbit (it makes about as much sense as the rest of the book) and he has a very good bit on the temperature including a bit on the why measuring temperature in space is a bit hard unfortunately it is a book only chapter so I can not link you the web site (they are worth a read anyway being funny and informative) I will try to find the explanation and copy it here but as a book suggestion I recommend it


    Last edited: Jan 3, 2017
  26. Trailblazer

    Trailblazer Moderator Staff Member

    The entire Earth has been hanging in space for a lot longer than 15 years, being heated constantly by the sun, and yet it has neither boiled away nor frozen into a giant popsicle. Same goes for the moon.

    Edit: and I see now that Mick made exactly the same point in post #4! :rolleyes: Read his posts at the top of this thread and you will understand about radiative equilibrium temperatures.
    Last edited: Jan 3, 2017
  27. motive99

    motive99 New Member

    But if you are being honest you aren't using the 'same flame'. The source of heat that will heat a single molecule comes from the gamma, xray, and ultraviolet radiation coming from the sun. If the source of heat has the potential energy to excite a single particle to upwards of 2500 degrees C and that source (sunlight) is constant throughout the entirety of the exposed particles subjected in the thermosphere then it will be applied equally to any molecule exposed to that sunlight whether it stands as a single particle alone or as any particle subjected to the whole of the electromagnetic spectrum connected to the entire sunlit side of the spacecraft.

    To be fair and to apply your analogy correctly the 'flame' would not be the tiny flame submerging the needle 'in' the flame, but it would have to be expanded to the whole of the kettle and for the sake of your visual argument the entire kettle would have to be 'submerged' in the flame at the same temperature as was the needle to fit your argument correctly, therefore any amount of sufficient cooling radiation needed to cool the craft would have to be increased by the amount of simultaneous kinetic energy being produced by the billions-trillions of particles composing the entire sunlit side of the craft. Furthermore that energy would be consistently radiated into the colder areas of the craft before radiating into any shaded area of the vacuum caused by the size of the craft unless we don't believe in the second law of thermodynamics anymore. You created a logical fallacy to deceive the reader. His question still stands.

    The kinetic energy produced on the exposed side of the spacecraft would excite ALL exposed particles to (upwards of) 2500 degrees C to the light of the sun simultaneously which would magnify the needed thermal cooling radiation due to the vacuum by literally the billions-trillions of particles being consistently exposed to those temperatures. The sun isn't directing a particle sized beam of light to each individual particle of atmosphere to heat them it is sending an array of light to all areas of space subjected to sunlight, just as your flame isnt engulfing a tiny needle and remaining the same size flame allowing the mass of the kettle to provide thermal cooling radiation to its surrounding cool atmosphere.

    [impolite text removed]
    Last edited by a moderator: Feb 28, 2017
  28. Trailblazer

    Trailblazer Moderator Staff Member

    Why would you think that? Ever touched the roof of a black car and a white car in the same parking lot in summer? Same incoming energy radiation, very different temperature.

    I do agree though that the flame analogy isn't really applicable here. Flames heat by conduction, not by radiation.
    Last edited: Feb 28, 2017
  29. Spectrar Ghost

    Spectrar Ghost Senior Member

    It's not really appropriate to talk about changing the temperature of a particle, since temperature is the RMS kinetic energy of a group of molecules.

    In any case, such high energy events are taken into account when the solar irradiation is calculated. Also, Gamma and X-Ray are a very small portion of solar radiation. In fact, Gamma and X-ray radiation from the sun originates solely in the photosphere, the outermost layer of the sun. Gammas in particular are only seen when produced by solar flares. While Fusion produces gamma rays, the energy of these rays is gradually sapped in the several thousand year journey to the sun's surface until they are mostly in the visible spectrum.


    Last edited: Feb 28, 2017
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  30. motive99

    motive99 New Member

    I do believe that your analogy is meant to downplay the effect of extreme heat we are discussing and also to imply that the impact of radiative energy applied by the sunlight would affect different elements composing the satellites to different degrees of intensity based on the reflectivity and the elemental differences of the material being exposed. I do remind you that we are speaking of a consistent stream of (potentially upwards of) 2500 degree C temperature. Mylar reflects rays of light, as does Gold, as does the color white, as does the color black if it is made of any form of matter. That does not, however, account for the potential extreme for temperature exposure in the thermosphere. These all have reflective properties that prevent some<<<absorption>>> of the light spectrum, but let's remember that the atoms, molecules, particles what have you will still be exposed to that heat. All of these elements have a melting point when exposed to certain temperatures regardless of reflectivity and as I demonstrated above the temperature of the sparse ionized gasses are not the driving issue at hand, it is the radiative heat of the sun.

    Gold has a melting point of 1064 degree C
    Mylar has a melting point of 260 degree C
    Aluminum has a melting point of 660 degree C

    Many other materials made of far weaker materials are composed together on the outer structure of the crafts that have existed in the stratosphere and supposedly beyond including the suits of the astronauts.

    The only element possibly capable of withstanding the highest potential temperatures in the thermosphere is carbon coming in at a melting point of 3550 degree C.

    If you want to really get into fancy technology, NASA has a spray coating called az-2000-iecw that can withstand temperatures of upwards of 1000 degree C.

    My point is this - we can talk all day about vacuum surroundings, the radiant flux, convection, conduction, or radiative cooling. Before the discussion of heat transfer and radiative cooling takes place we need to address the first question. What causes these materials to withstand direct contact with thermospheric temperatures since it is established science everywhere (besides the NASA official page that discusses how satellites deal with cooling their satellite crafts) that the potential kinetic energy of the sun in the thermosphere ranges from 500 degree C to 2500 degree C.

    Let's start with that and end the deceptive analogies since this is supposed to be a board about dealing with facts?

    I honestly don't care what the answer is and I am not a space denier or flat earther or anything else other than someone who encourages the spark of curiosity and independent research that this sort of questioning realizes in common people - therefore, I am thrilled with the rising skeptic attitude towards the issues that common humanity has all too often historically accepted as facts from authority figures such as the nature of the reality we all live in. Questioning skeptically demands independent investigation and leads to a more knowledgeable society.

    I'd like an honest conversation because there is a high level of distrust concerning NASA in my opinion for some very compelling reasons. This might not be the place to do it, but I am engaged in this conversation here for no other reason than to be a voice to be heard for the passer by who discovered this topic due to a question in a search engine. I am already well aware of the area of the internet I am speaking in. Hello deep state.
  31. motive99

    motive99 New Member

    We are talking semantics here. For the laymen your rms kinetic energy is a fancy way of saying the average speed and mass (aka temperature) of a specific gas molecule. You said the same thing I did I was only referring to simply particles because molecules are typically broken into ionized particles by the great power of the sun in the thermosphere.

    Whether a particle or molecule, vibrational states can be defined as heat unless we are talking about something like quantum differentials. In the case of the thermosphere the sun typically breaks any molecules into atomic nitrogen oxygen or helium.

    I'm not sure what you're referring to when you say such high energy events are taken into account when solar irradiation is calculated, I presume you are dancing to the idea that nasa already took that into consideration so theres nothing to look at.

    I included gamma rays and x-rays and stopped with ultraviolet to save you from reading the list (and excluded example radio waves for intuitive reasons) because they do have an effect however minimal, just as many are including the heat transfer of atmospheric particles into the discussion however minimal their effect may be as well. Regardless, the heat is still right there in the thermosphere regardless of the availability in range of present wavelengths in the electromagnetic spectrum.

    I'm just interested in finding a concrete and understandable answer to the first question and we can go from there. I'm not a fan of Albert Einstein, but I agree when he said if you cannot explain it simply you do not understand it well enough. NASA or somebody should provide an understandable answer to the many peoples questions about temperature resistance in the thermosphere. We sure are paying them enough to hire some people to really go after addressing questions in a more suitable fashion.
    Last edited: Feb 28, 2017
  32. Trailblazer

    Trailblazer Moderator Staff Member

    I think you need to explain what you mean by this. The sun is not in the thermosphere, so how can the sun have "potential kinetic energy in the thermosphere"? The thermosphere is just the name given to an area of the far upper atmosphere.

    The amount of solar radiation in the thermosphere is no different than the amount of solar radiation anywhere in deep space at an equivalent distance from the sun (radiation falls with distance under the inverse square law, so it is inversely proportional to the square of the distance from the sun).

    There's nothing special about the thermosphere. The radiative equilibrium for a spacecraft in the thermosphere is no different from that for one in deep space on the opposite side of the sun from the Earth, at the same distance.
  33. motive99

    motive99 New Member

    The sunlight in the thermosphere not the sun itself.

    And the radiative equilibrium is an item in question that can be discussed once the first question of materials withstanding the initial and persistent contact to the radiative heat of sunlight is determined. Radiative equilibrium is a functional term coined for solar objects like the earth but there are many other factors at play concerning the earth. The question at hand here are the physical man made materials in the thermosphere. What is special about the thermosphere is the fact that it is where the vast majority of our space craft reside, which is why it is the location in which this discussion is taking place. It is also special or unique in a way concerning this topic because there are factors that don't exist in the exosphere and beyond - like atmospheric particles that provide examples of the power the sun has on particles exposed to sunlight that aren't otherwise protected by the denser layers of the atmosphere. This example is not present outside of the thermosphere.

    I am aware that the sun sends its radiation in all directions..
    Last edited: Mar 1, 2017
  34. Trailblazer

    Trailblazer Moderator Staff Member

    So do you think a spacecraft in deep space, outside of the thermosphere but at the same distance from the sun, would get hotter or colder than one inside the thermosphere?

    And for the one which you think would be hotter, where would the extra heat energy be coming from?
  35. JohnJones

    JohnJones New Member

    Mick's 2015 post is quite correct, and the radiative equilibrium temperature for a black body in the thermosphere will be around zero Celsius. The mystery that is puzzling abishua and motive99, and which we haven't explained so far, is why individual gas molecules and atoms in the thermosphere get so much hotter than this.

    The explanation is that isolated atoms and molecules are not black bodies. When an isolated atom in the thermosphere is struck by a photon, the energy transferred to it by the photon can appear in one (or both) of two forms: the excitation of an electron in the atom to a higher orbital, or translational kinetic energy of the atom as a whole. In the former case, the electron will eventually fall back to a lower orbital, re-emitting a photon. But the translational kinetic energy of the atom will remain in that form until the atom collides with another atom. When such a collision occurs, some of the kinetic energy may be converted to the excitation of electrons, which may subsequently fall back to ground state with the emission of photons.

    In the thermosphere, such collisions are rare; at an altitude of 500 km, a particle travels an average of 100 km between collisions. So the energy that an isolated atom absorbs gets "stuck" in the form of translational kinetic energy, and the average kinetic energy of these particles corresponds to a temperature of thousands of degrees.

    Once one of these molecules strikes a larger object, the energy of the collision is converted to one of the many internal modes of energy storage available to solid bodies, such as molecular vibration, and any excess energy above the radiative equilibrium temperature is quickly radiated away as emitted photons.

    Why doesn't the same argument apply to gas molecules and atoms lower in the atmosphere? The chief reason is that they're much closer together - at ground level, the typical distance travelled between collisions is about a tenth of a micron rather than 100 km - so they very rapidly go through a series of collisions which allow their translational kinetic energy to be converted to electronic excitation and hence to photon emission, providing radiative cooling. (There's also the fact that the incident solar radiation higher in the atmosphere contains more high-energy UV photons, as illustrated in Spectrar Ghost's chart.)
    Last edited: Mar 1, 2017
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  36. Trailblazer

    Trailblazer Moderator Staff Member

    Good explanation @JohnJones. The key concept is "mean free path" which is a measure of how far a particle will travel, on average, before it hits another.

    As an analogy, consider striking the cueball into the pack on a pool table. The balls will bounce around in all directions, smashing into each other and the cushions, and fairly quickly all motion will cease as the energy gets dissipated.

    Now, place the cueball on the floor in the middle of a vast empty sports hall and strike it with the same force. The ball will keep rolling and rolling, maintaining its speed ("temperature") for far longer, because it won't hit anything until it eventually reaches one of the walls.
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  37. motive99

    motive99 New Member

    I see that your consistent analogies are getting pats on the back yet mine are getting nothing at all, I find that interesting.

    JohnJones it seems to me that you are misunderstanding the definition of radiation and also the accepted theory for the cause of heat in the thermosphere if you are claiming that translational kinetic energy is the reason for high temperatures in particles in the thermosphere. You are claiming that basically the reason the temperature is expressed as extremely high in the thermosphere is because of the measurement of the distance a single particle travels (translational kinetic energy=1/2mv^2) in space after contact with a photon due to the lack of a resistant force like other particles/molecules that would otherwise cause vibrational kinetic energy instead due to bouncing off other particles. I can throw in equations of measurement to make my argument sound more legitimate as well even though it does not help illustrate a concept guys. This is either an extremely deceptive way of explaining this or you don't accept the accepted scientific reasoning for radiative energy in the thermosphere at all. The radiative energy is coming from a 3rd party source - the sun. It does not make the energy any LESS because it is interacting with a mass of molecules or a single particle just as the measurement of kinetic energy interacting on the particle or molecule isn't any LESS because of the form of kinetic energy being expressed in said molecule or particle. Here is the definition of what the real science says about the heat in the thermosphere from several sources:

    Thanks NASA for talking to us like we are the dumbed down population that your sister agency the Department of Education has made us.


    So, you see, the actual radiative temperature in the thermosphere is DEFINED as upwards of 2500 C because of the heat of the sun. It is NOT a temperature that is merely expressed due to translational kinetic energy of a single particle due to the lack of surrounding mass, nor is it defined as 'not really actually hot because there's not that much stuff up there'. It is actually, really, no really guys I mean actually really hot!

    It is true a billiard ball will not travel a distance to express the energy enacted upon it if it is in rack. That does not make its energy any more or less if enacting upon other balls. The first ball in the rack enacted upon by the cue ball interacts with the same energy it would have had it not had any resistance of travel. The energy is still there it is not LOST. It is instead expressed as vibrational kinetic energy instead of translational because it transfers the energy to the other balls. For this, all three of Newtons laws of motion come into play. Incase you forgot them; The laws are: (1) Every object moves in a straight line unless acted upon by a force. (2) The acceleration of an object is directly proportional to the net force exerted and inversely proportional to the object's mass. (3) For every action, there is an equal and opposite reaction.
    ALL the same basic concepts can be visualized with heat and force using the laws of thermodynamics which we were discussing earlier, but alas, the analogy was physical force and billiard balls instead of heat and energy.

    Now that I have shown your analogy to once again be inapplicable to this and a radiative equilibrium of 0 C being unfounded unless there is some other scientific explanation that has yet been presented here... the next question is how does 2500 C radiation not transfer to the body of the craft due to the 2nd law of thermodynamics? The 1st law says that energy cannot be created or destroyed. This would mean that the temperature should be transferred into the craft. For the entire side of the craft being subjected to upwards of 2500 C would mean that the radiative equilibrium should eventually balance at whatever mean temperature the craft is experiencing due to the force of the SUN and not the silly little gas particles zooming around. Radiative equilibrium is not a 1 way street.
  38. Trailblazer

    Trailblazer Moderator Staff Member

    You are quoting from a site called "study.com" that appears to be not very rigorous (to put it kindly). The passage you quote is full of errors.

    Take this excerpt:

    Not only does this directly contradict the Wikipedia page that you quoted just above it, which states "Thermospheric temperatures increase with altitude due to absorption of highly energetic solar radiation", but a moment's consideration will tell you that it is nonsense.

    If there is "no absorption of the heat from solar radiation", then how can "temperatures soar"? To make things hot, they have to absorb heat energy. And anyway, temperatures of WHAT? Electromagnetic radiation (such as sunlight) in and of itself does not have a "temperature". You can talk about the effective black-body temperature of radiation, which is the temperature a black body would have to have in order to emit the same radiation spectrum, but this is not a measure of temperature as we know it.

    For example, sunlight has a black-body temperature ("colour temperature") of about 5,800 kelvin, or 10,000 degrees Fahrenheit. Does that mean sunlight will heat you up to that temperature if you stand in it? Of course not.

    You may recognise the term "colour temperature" from the packaging of lightbulbs:


    Notice that a "cool white", or daylight, fluorescent bulb has a colour temperature almost the same as the sun (that is what it is designed to mimic). That doesn't mean it will heat you up to 10,000 degrees Fahrenheit if you stand under it! The monitor you are looking at now probably has a colour temperature higher than that of the sun, maybe 6500 kelvin. How are your eyes coping with that searing radiation?


    No it isn't. There is no such thing as "the radiative temperature" unless you define what you are measuring the radiative temperature of! If you put a piece of shiny aluminium in the thermosphere, it will have a radiative temperature somewhere below zero Celsius. If you put a matt black painted piece of plastic there it will probably be somewhat higher. If you put a helium or oxygen atom up there and it gets zapped by an X-ray and ionised, then it may attain a temperature of a couple of thousand degrees Celsius because it will go whizzing off at high speed until it eventually hits something. If the same X-ray strikes an atom in the hull of a spaceship then it might knock an electron loose, the energy will quickly be absorbed by the other neighbouring atoms, the electron will find a new home, the heat will be re-radiated back into space, and not much else will happen.

    Space doesn't have a temperature*. Radiation doesn't have a temperature. Physical objects have a temperature, that depends greatly on their properties.

    I am still at a loss to understand why you think the thermosphere is a special extra-hot place. What makes the solar radiation in the thermosphere so much stronger than, say, the solar radiation on the moon, or out in deep space? The sun only puts out a certain amount of energy. If it could heat stuff up to 2500C in the thermosphere then surely the Earth and the moon ought to be glowing white hot as well, after all they're at a similar distance from the sun, right?

    * well, unless you count the cosmic microwave background radiation, but that's less than minus 270 Celsius, so astronauts are still going to need to pack thermals.
    Last edited: Mar 3, 2017
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  39. Trailblazer

    Trailblazer Moderator Staff Member

    You can actually calculate how hot sunlight can possibly make a bulk object at a given distance from the sun, using the Stefan–Boltzmann law.

    i won't go into the maths (unless anyone really wants to know), but assuming a perfect "black body" that absorbs all radiation that falls on it, then the equilibrium temperature T is:

    T = Tsun (r/R)½

    where Tsun is the surface temperature of the sun (5,800K)
    r is the radius of the sun (695,000km)
    R is the distance to the sun (which for the Earth is 1.5 x 108km)

    Plug in the numbers and you get:

    T = 5,800K x (695,000km / 1.5 x 108km)½

    = 395K.

    395 kelvin is 122º Celsius, or 251º Fahrenheit. (Coincidentally - or not! - this is also the maximum temperature of the moon's surface during lunar daytime.) Your satellite is not going to get hotter than about 250ºF, even if you give it a blinging matt-black paint job.
    Last edited: Mar 3, 2017
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  40. Henk001

    Henk001 Active Member

    1. The main point is that to heat something up (to raise the temperature), you need energy. Every molecule of the thermosphere in itself carries only a tiny bit of energy. In order to raise the temperature of a satellite you need a lot of collisions with molecules, but they are sparse there. Therefore you won't notice its high "temperature" at all.
    2. For a body like a satellite, with a lot of mutually interacting molecules packed together, you have radiative equilibrium, but not for a single molecule; so it is wrong to assume that the average kinetic energy of those single molecules has anything to do with the equilibrium temperature caused by the incoming and outgoing radiation.