<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>The density of the atmosphere (air which includes water vapor) is so low up there, here on earth it would be considered a vaccuum. There aren't enough water molecules to make drops. Besides, at that temperature it would be ice, not water, but because of the low pressure they dissapate very fast.When the shuttle dumps excess water (which it has to do occasionally) the liguid instantly freezes into ice particles which create a cloud around the shuttle. For those that Have seen it, it's quite a spectacular sigyht form the ground, since the ice reflects sunlight. But within minutes, the ice sublimates into gas and is spread out so much it can't be seen any more. <br />Posted by MeteorWayne</DIV></p><p>You have your finger on the basic issue which is pressure.</p><p>Let's keep this discussion classical (no quantum vacuum stuff, etc.). Temperature is the average kinetic energy per molecule per degree of freedom in a substance, or what is the same thing it is the average kinetic energy of translation of the molecule. The notion of temperature is thermodynamic and hence statistical in nature and only applies to reasonably large collection of molecules. In a vacuum there are not enough molecules, ideally none, to make temperature a viable concept. So space is not really neither cold nor hot, though objects in space can become very cold due to radiation to the background or very hot due to absorption of energy from the sun, or hot on one side and cold on the other -- see below.</p><p>Space does have some photons that can provide energy via radiation. And it can serve to accept photons emitted by a body in space. So you immediately have some radiative heat transfer going on. But for materials at moderate temperatures that radiative loss of heat is relatively slow (i.e. no great amount of heat is lost or gained essentially instantaneously).</p><p>But a liquid like water thrown into space has a temperature, and that temperature is reflected in a bunch of molecules moving around at various speeds. the distribution of speeds being determined by the temperature, or vice versa. And in space there are no other water molecules flying around that could potentially hit and enter the glob that is thrown out. In fact there are no outside water molecules to the ambient partial pressure of water is 0, but the pressure in the glob is something larger than 0. So what happens is that the faster, hotter molecules escape to the vacuum and the cooler ones are left behind. That is called boiling. Just as water boils at a lower temperature on top of a mountain than it does at sea level (ever try to cook rice at 11,000 ft ?) so water in space boils at a VERY low temperature. When the hotter molecules escape, depart the area, and leave the cooler ones behind the glob cools, this is called loss of heat of evaporation. That happens really fast, since the ambient environment is a vacuum. When it cools enough it freezes into a solid. But ice also has a vapor pressure since the molecules sitll have kinetic energy and are not completely bound to one another and they are still in a vacuum. So the solid glob continues to loose molecules (sublimation) and continues to cool. In short order it disappears due to continued sublimation. <br /></p> <div class="Discussion_UserSignature"> </div>
Basic Error: The accelerating Universe conclusion - reason
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