Thermodynamics for Moon Man

[Glom]

I need to find out where we stand. Moon Man,

1) Do you understand the difference between heat and temperature?

2) Do you know and understand the basics of the three types of heat transfer?

[Moon Man]

Go ahead and explain it.

[lonewulf]

By Moon Man:
Go ahead and explain it.

For the love of (insert deity here), WHY?!

While I'm impressed that people have shown such an astounding level of patience with Moon Man... why this post? It's useless! He'll just disregard everything as saying, "I don't believe it's plausible, so it must not be"!

[Moon Man]

Not so, but thanks for you vote of confidence.

[Glom]

Heat is a measure of thermal energy. Temperature is a measure of the motion of the particles in an object. You will note the term "object". No object = no temperature. Vacuum does not have a temperature just as it does not have a colour or a smell. Heat will determine temperature through the heat capacity, which varies from object to object.

Convection is the most effective form of heat transfer. It depends on gravity. Fluids that heat up expand and rise, carrying their heat with them. This motion in the fluid allows for the rapid transport of heat.

Conduction is the process of heat being transferred through an object as oscillations transmit energy to the neighbouring particle. Mobile electrons assist this, which is why good electrical conductors are also good thermal conductors.

Radiation is the least effective. It depends on object emitting photons to move the heat around.

Convection, being the most effective, is the basis for a lot of the heat transfer in everyday life. Because it can transport heat rapidly, it helps to smoothen out temperature variations by moving heat from hotter objects to cooler objects. The only problem is that it needs a fluid, such as an atmosphere.

On the moon, there is no atmosphere, hence no convection. This means that temperature variations from object to object remain stark without convection to smoothen them. Heat transfer on the moon is mostly due to radiation and so how hot an object gets depends on how much energy is emits and absorbs, which is dependent on the radiant environment and the optical properties of the object.

[Moon Man]

Thanks for taking the time to post that Glom.

I have a few questions that are not really related.

Do you believe it is not cold in space or do you believe the temperature is simply not measurable..?

Lets say it's a sunny 220 degree day. What would the temperature be in a shadow..?

If you say it's not measurable because only an object is subject to a temperature then just tell me if you believe it would still 220 degrees in the shade..?

Do you believe that on a bright sunny day that there would be shadows cast from an astronaut..?

If you say it depends on what time of day then assume the sun is at it's highest point.

Do you believe the sun shines brighter on the moon than it does on earth..?

[mushiwulf]

"It" is a pronoun. Could you specify what noun you are referring to please?

[Moon Man]

What do you mean, I have lots of it in there..?

[AstroSmurf]

The temperature of an object in vacuum would depend on:
* The amount of sunlight shining on it (assuming "outdoors", this is the easy part)
* The reflectivity of the object, i.e. how much sunlight is bounced straight off it without heating it
* The heat capacity of the material it's made from.
* If there are any other sources of light/heat around it (an object inside the LM would try to assume the same temperature as the hull if left to itself).
* How well it radiates heat out to space
And, assuming the time it's been there is fairly short:
* Its original temperature before brought into the vacuum
* How long it's been sitting in the light

Further, the distribution of heat within the object would also depend on if and how it's been moved around relative to its surroundings.

So you see, there's no easy quick answer to the question. We can give a ballpark figure for the lunar surface because most of those questions have well-known answers for that situation, but they won't necessarily apply to anything else.

[AstroSmurf]

Oh, I forgot two things:
* The shape of the object and how it's oriented towards the sunlight
* The size of the object (larger objects naturally take longer to change temperature)

[RAF]

moonman said:

Do you believe that on a bright sunny day that there would be shadows cast from an astronaut..?

Could someone kindly tell me what in the heck MM is talking about??

[politik]

Do you believe it is not cold in space or do you believe the temperature is simply not measurable..?

The temperature is not measurable. Its not a belief either. It is an unfortunate fact for you. You cannot measure the temperature of nothing. The only thing you can measure is how a particular object will react to a particular environment. IE an object in the shadow of the sun will be colder than an object in direct sunlight.

Lets say it's a sunny 220 degree day. What would the temperature be in a shadow..?

Same answer as the first question.

If you say it's not measurable because only an object is subject to a temperature then just tell me if you believe it would still 220 degrees in the shade..?
Again, temperature is meaningless without matter. The only thing you can measure is the temperature of an object or matter. If it is in the shade, it will have a lower temperature -- eventually. If an object is brought from direct sunlight into shadow, then the object will have lost its primary source of heat and will start to radiate more heat than it receives.

Do you believe that on a bright sunny day that there would be shadows cast from an astronaut..?

I can only guess what you are asking here, but yeah a shadow should be cast direct behind ANY object in direct sunlight. How that shadow appears on a surface or object behind the object casting the shadow is an entirely different matter.

If you say it depends on what time of day then assume the sun is at it's highest point.

Do you believe the sun shines brighter on the moon than it does on earth..?

The sun should be brighter on the moon. Lack of an atmosphere to block incoming light would affect luminosity. The angle at which the sun strikes the surface and the type of surface will ultimately have the greatest effect on what the resulting temperature.

[Moon Man]

Thanks politik.

The first question warrants elaboration. Nevermind temperature readings. Is it cold in space..? I say yes, others have said yes, while others have said no it's not cold.

[LunarOrbit]

For the billionth time... space is not hot or cold, it is nothing. Objects in space can be hot or cold depending on how much sunlight they are exposed to and how much heat they generate on their own. You have to specify what kind of object you want to know the temperature of since different objects will have different temperatures, even under identical circumstances.

Why can't you understand that?

[echnaton]

moonman said:

Thanks politik.

The first question warrants elaboration. Nevermind temperature readings. Is it cold in space..? I say yes, others have said yes, while others have said no it's not cold.

There is no air in space so there is no measurable temperature as we are accustom to measuring on earth by putting a thermometer outside. We are frustrated because you won’t plainly answer simple questions needed to understand what you really mean.

Just answer this question. The temperature of what in space?