moon heat

so if I understand this correctly:
someone standing on the moon under a big tent,
would not feel warmth, even though the temperature of the tent fabric
was 110 f .

but when moon guy stepped in to the sun light,
he would only feel the warmth, on the side of his suit that faced the
sun, not the dark side of his suit.

confirmation requested

Heat can be transferred by three methods: radiation, conduction, and
convection. In the absence of air, convection is eliminated. Your
astronaut under the tent might pick up a little residual heat from the lunar
soil, and when he stepped outside, the fabric of his spacesuit might conduct
heat from the light side to the dark. But most of the heat he'd feel would
come from direct exposure to sunlight (radiation).



"Az Trekker" wrote in message
...
so if I understand this correctly:
someone standing on the moon under a big tent,
would not feel warmth, even though the temperature of the tent fabric
was 110 f .

but when moon guy stepped in to the sun light,
he would only feel the warmth, on the side of his suit that faced the
sun, not the dark side of his suit.

confirmation requested

Hi AZ Orbital patterns tell us that most sectors of the moon spend
about two Earthly weeks in sunlight and two in darkness. I'm lookihg
down showing a major depression surounding the south pole it looks
deep,and it is said that this would be the best place to find traces of
cometry ice. AZ pictures taken when the sun is low show stark relief.
Some of the moon's craters half in light,and half in vivid shade. Moon
without an atmosphere must have great temp. change in just a few
minutes. Would be a good place to freeze-dried foods. Calling its
desert surface freeze-dried fits Sad part is when we walk on the moon
we are not actually touching it. Who needs an expensive actor when
hollywood makes a movie showing the exploration(men walking on the moon)
when all we see is a white space suit. Bert

"Az Trekker" wrote in message
...
so if I understand this correctly:
someone standing on the moon under a big tent,
would not feel warmth, even though the temperature of the tent fabric
was 110 f .

but when moon guy stepped in to the sun light,
he would only feel the warmth, on the side of his suit that faced the
sun, not the dark side of his suit.

confirmation requested

Anything warm radiates heat, so the tent fabric and lunar surface would have
some effect.

DFC

"Az Trekker" wrote in message
...
|
| confirmation requested

That's basically correct.

As Bill pointed out, you have three modes of transferring heat between
masses: direct contact, convection through a fluid that contains both
masses, and radiation.

On earth convection plays a big part in how we experience heat. In most
natural settings the heat ultimately derives from the sun, which transfers
heat to earth via radiation. But air spreads it around.

So let's say you were standing under a big tent. For simplicity, we'll say
the tent is opaque. And also we'll simplify the problem by saying that the
tent has been there long enough to remove the effects of solar heating from
the soil -- it's been in shade for long enough. Let's also assume that the
tent has walls, so that while you're standing in the tent you can't see any
portion of the lunar surface.

Now the sun beating down on the tent will heat the tent fabric. The fabric
will reflect away some of the energy and absorb the rest. How much of each
depends on the optical properties of the tent. If the tent is polished
aluminum, it will reflect away almost all the energy. If it's made of
dulled carbon, it will absorb most of it. It also depends on how directly
any one portion of the tent fabric faces the sun. If the sun is directly
overhead and the tent shape is roughly cubical, the roof will get hotter
than the walls.

As the tent fabric gets hot it will begin to conduct heat within its mass.
Hot parts will transfer heat via conduction to cooler parts. The parts that
touch the lunar surface will transfer heat in one direction or another,
depending on which is hotter. The fabric will also radiate heat away as
infrared energy. It will do this in both directions -- back into space, and
into the interior of the tent.

Now if we assume the tent is unpressurized, that radiation is the only way
by which heat can be transferred to you. And it won't be very much;
radiation is not a very efficient way of transferring heat compared to
convection and conduction.

Now theoretically the sun shining on the lunar soil outside the tent will
heat it. And those particles will transfer heat to particles that touch
them, and by radiation to those nearby. In theory some of that heat will be
transferred under the tent through the lunar surface.

I say "in theory" because the amount that could be practically transferred
that way is negligible. A theoretical path exists, but no measurable heat
makes it through. Think of lunar dust at the micrscopic level. It's a
bunch of odd-shaped particles touching each other. Now the amount of heat
that's conductively transferred from one object to another depends on the
total surface area in contact, and between pointy lunar dust grains there
isn't much contact area. On earth these particulates would not only touch
each other, they'd be in a soup of atmosphere that greatly aids the transfer
of heat from particle to particle. On the moon, even though surface
temperatures can reach more than 240 F, you only have to dig down a few
inches to find material that's below freezing.

So the greatest source of external heat to you in your tent is the small
amount radiated from the inside of the tent fabric as it gets hot.

As you step outside, you're immediately subject to direct radiant heat
transfer. From the sun, directly, that's a pretty large amount. Whether
you feel the warmth depends on how well your suit is designed. Space suits
are designed to be highly reflective. So most of the energy from the sun
that hits you is reflected away. And suits contain many layers of thermal
insulation. Insulation means heat doesn't travel very well between the
layers. So even if the outer surface of your suit gets up to 100 F or so,
you won't necessarily feel in inside all those layers.

You might get a little heat through your feet, if you stand on the surface
for too long. But chances are you probably won't feel any heat conducted
from the sunlit surface.

The problem with the space suit, ironically, is how to get rid of heat.
We've discussed the heat transfer into the suit. The problem is that the
human body is itself a source of heat. Metabolism creates heat, and on
earth that heat is carried away largely by the air through convective
cooling aided by evaporation of perspiration. If you put a person in a
space suit that's heavily insulated to keep heat from getting in, you have
to figure out what to do with the heat that's being generated from inside.

The solution is the porous plate submlimator that formalizes and carries to
the next level the same heat transfer processes that your body naturally
uses to cool itself in its habitual environment.

The best way to feel the warmth of the sun in space is to raise your tinted
suit visor and let most of the sun's wavelengths fall directly on your skin
through the clear portion of your helmet. But since those wavelengths
include far more ultraviolet than you get normally on earth, don't do that
for too long. You'll get a wicked sunburn.

--
|
The universe is not required to conform | Jay Windley
to the expectations of the ignorant. | webmaster @ clavius.org