Why is space cold?
Name: susan b hieber
Date: 1993 - 1999
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?
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".
...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?
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...
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Update: June 2012