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quote:Much of outer space has the density and pressure of an almost perfect vacuum. It has effectively no friction. The properties of the vacuum remain largely unknown.A perfect vacuum is an ideal state that cannot practically be obtained in a laboratory, not even in outer space, where there are a few hydrogen atoms per cubic centimeter at 10#8722;14 pascal or 10#8722;16 Torr.All of the observable universe is also filled with large numbers of photons, the so-called cosmic background radiation, and quite likely a correspondingly large number of neutrinos. The current temperature is about 3 K, being merely 3 kelvins or degrees Celsius above the absolute zero of temperature. Neither these photons nor the neutrinos produce a significant interaction with matter, so stars, planets and spacecraft move freely in this near perfect vacuum of interstellar space.Stars, planets and moons keep their atmosphere by gravitational attraction, so atmospheres have no firm boundary. The density of gas decreases with distance from the object. In Low Earth Orbit (about 300 km altitude) the atmospheric density is still sufficient to produce significant drag on satellites. Most Earth satellites operate in this region, and they need to fire their engines every few days to maintain orbit.Beyond planetary atmospheres, the pressure from photons and other particles from the sun become significant. Spacecraft can be buffeted by solar winds, but planets are too massive to be affected. The idea of using this wind with a solar sail has been proposed for interplanetary travel.The deep vacuum of space could make it an attractive environment for certain processes, for instance those that require ultraclean surfaces.In 1913, Norwegian explorer and physicist Kristian Birkeland may have been the first to predict that space is not only a plasma, but also contains "dark matter". He wrote: "It seems to be a natural consequence of our points of view to assume that the whole of space is filled with electrons and flying electric ions of all kinds. We have assumed that each stellar system in evolutions throws off electric corpuscles into space. It does not seem unreasonable therefore to think that the greater part of the material masses in the universe is found, not in the solar systems or nebulae, but in "empty" space.
quote:Originally posted by another_someoneThere is no such thing as a perfect vacuum. Even interstellar space, and no doubt intergalactic space, contains some matter, just very little of it.
quote:Originally posted by neilepThank You tony..yes that helps.Thank you George. I can see now how an absolute vacuum is an unatainable circumstance.Though...the circumstances may prevail for such a void somewhere in the Universe.........UKMickeys head !!! for instance..hee hee..shhhh don't tell him I said that !!..hee hee  Men are the same as women, just inside out!
quote:Empirical study time. Iíve got an interview and an assessment tomorrow for a managerial position during which the conditions for creating a perfect vacuum in my head should be optimum. Hopefully for me and the future of mankind George is correct in his assertions,as I don't think my cranium is thick enough to withstand the pressure of a perfect vacuum. (you best be right George)Neil I shall let you know for certain tomorrow after the results come in ,but judging by all the neuron or should i say neurotic activity going on in their tonight as I wait nervously I feel you could definatly be wrong. I HOPE Michael
quote:Originally posted by neilepHow can there be a Solar Wind in the vacuum of space ?...does the same apply to shock-waves too ?
quote:Originally posted by neilepThe premise behind my original post was that the term ' wind ' was a misnomer regarding the nature of what I thoguht was the vacuum of space.In that 'wind ' is like a gust of air that you feel on your face..... Open Space...being atmospherically unfriendly, I thought the term ' wind ' was inappropriate....however, as George has enlightened me otherwise...even in the depths of space a vacuum is nigh on impossible.....so what about shock waves then ?...I presume the same applies eh ?.....but on a lesser scale...In other words...where one would get destroyed by a shockwave here on earth......would one be able to survive the same in deep space ?