Why is space cold? ```Name: susan b hieber Status: N/A Age: N/A Location: N/A Country: N/A Date: 1993 - 1999 ``` Question: My fourth grade class would like to know why outer space is cold when some parts of outer space are closer to the sun than the Earth?. Also, is the outer space just outside the Earth cold too? Replies: But outer space is NOT cold. The matter in outer space is really very hot; there just isn't much of it. I suggest that you and your class investigate the meaning of the notions of "hot" and "cold". J Lu ...and remember that heat is energy and this energy can be transfered by conduction, convection, or radiation (just real basic thermodynamics). In space there is virtually no medium for conduction or convection (actually, the tenuous plasma and gas that permeates space has an extrememly low heat capacity), so a body in space gains or loses heat by radiation. In fact, all bodies radiate heat according to their temp. (black body radiation, look it up); if a body radiates more than it absorbs, it cools off, like a satellite in Earth orbit while it's in the Earth's shadow (from the Sun). If you're in direct sunlight, you will heat up unless you're a very good reflector! The short, simple answer is that being hot or cold is a property of matter... AND hot or cold RELATIVE to what? Hawley But, Hawley, remember that you're talking to 4th graders (and a teacher who is required to be a generalist). I may be wrong, but I just don't think that words like "heat is energy", "conduction, convention -sorry - convection, and radiation", tenuous plasma" , or "heat capacity", mean very much to people at this level. You can get a better idea of the kinds of words that are meaningless, even to highly selected college freshmen, by reading Arnold Arons' book A Guide to the Teaching of Introductory Physics. As I say, I may be wrong, but I suspect that your comment was more intimidating than helpful. And, the temperature scal e IS absolute! Don't forget the golden rule , "Less is more!" Well, some of the matter in space is hot, some of it is cold (does anybody doubt that the outer planets, Pluto for example, are cold?) But "J Lu" is right that the matter between us and the sun tends to be pretty hot - in fact there's a lot of it streaming out of the sun in the solar wind. The solar corona reaches millions of degrees outside of the visible surface of the sun (the round disk where most of the light comes from, from our perspective, which is only around 5000 degrees K). But because those bits of matter (the solar wind in the neighborhood of the earth) are so widely dispersed, they don't amount to much energy and therefore MOST of the heating or cooling a person would experience in space near earth is through radiation. And then it's just like down here on earth, except a bit worse: when the sun is shining on you you get hot, when it's not, you get cold. The surface of the moon gets the full force of the sun for two weeks at a time, during which it really gets quite hot (at least a couple of hundred degrees F - I don't remember exactly) while during the "night" period for the moon, the sun doesn't shine at all and it gets very cold. (Of course, while it's night on one side of the moon, it's day on the other, but the moon doesn't have any atmosphere that can equalize the temperatures). . Oh, by "radiation" I meant the techin ... I meant the process where the sun shines on you and you get hot... A Smith Click here to return to the Astronomy Archives

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