Why is it so warm on the moon?

[losfomot]

Unfortunately I don't have a reference, (although I'm sure it would not be hard to find,) I recently read somewhere that temperatures on the moon during it's 'night' can reach minus (-) 150 degrees Celsius. This may seem extremely cold to some, but I don't understand this. If the moon has no atmosphere to keep heat in, then how does it maintain a temperature so high above absolute zero? Would a thermometer show a different temperature if it was hovering a foot off the surface compared to being in contact with the surface? And, if so, would that 'hovering' thermometer be colder?

Thanks

[Cap'n Refsmmat]

Sunlight heats it up.

 

The hovering thermometer probably would be colder, because it gets its only heat from solar radiation. Or, light bouncing off of Earth. With no atmosphere, the heat cannot escape from off of the surface except by radiation. And there isn't very much radiation on the moon. The light from the moon is just bounced off of the sun.

[swansont]

Would a thermometer show a different temperature if it was hovering a foot off the surface compared to being in contact with the surface? And' date=' if so, would that 'hovering' thermometer be colder?

Thanks[/quote']

 

With no atmosphere to give you conduction/convection to reach equilibrium, a thermometer is probably the wrong tool to measure the temperature.

 

As the Cap'n said, radiation is the only heating/cooling mechanism. The energy transfer goes as T⁴ - T₀⁴, so the sun heating the moon is more efficient than the moon radiating into empty space. There just isn't enough time for the surface to cool off more.

[Martin]

If the moon has no atmosphere to keep heat in, then how does it maintain a temperature so high above absolute zero?

 

 

losfomot, swansont said it but i can expand on that

 

there is a limit to how fast something can radiate its heat away

in a vacuum

 

(stefan-boltzmann fourthpower law with magic number sigma)

 

 

if it is hot it glows brightly and radiates lots of watts and gives up heat quickly

 

but as it cools it can only radiate fewer watts and the cooling process slows

 

maybe the moon rocks cool all night and are coldest just before

sunrise and then they get another shot of heat all day

and then they have to cool off again, by radiating into the darkness

 

so temp follows a sawtooth pattern

 

have to go, more another time

[Martin]

yeah Im back

swansont was beginning to talk about the fourthpower law

 

sigma is what tells how brightly hot things glow

 

to understand sigma you need the metric system of units----know what a square meter of surface area is, and what a watt of glow is, to measure the radiant power: watts per square meter.

 

the law is you take the temp in kelvin.

 

like say 1000 kelvin

 

and raise it to the fourth

 

1,000,000,000,000 kelvin⁴

 

and multiply by sigma

 

and that gives the watts per sq. meter!

 

sigma = 5.67 x 10^-8 watts per sq. meter per kelvin⁴

 

so if you have 10¹² kelvin⁴ and you

multiply by sigma you get 56,700 watts per sq. meter

 

but when something cools down to 100 kelvin then it sheds energy much more slowly, like 5.67 watts per sq. meter---by the same rule.

 

so cooling things taper off

 

even tho night lasts two weeks they dont have time to get

colder than whatever you said