Re: [Phys-l] paint your roof?

[Bernard Cleyet <bernardcleyet@redshift.com>]

We've been thru this before:

My, reported previously, hot tub cover frosts while the deck is only  
dewed and that's with still warm water below!

The side of my 'bile toward the brick wall is dry while the side  
toward the grass and the neighbor's grass and the roof are dewed.

All this would be clear if they'd read as a child george Gamow's  
books wherein one he relates the Arabs froze water in the desert  
overnight  by insulating the container.

> radiative
> coupling to something like the 2 pi steradians that aren't open
> "sky."

I think the principle of the dew shield.  [Restricts from 2 Pi to 3.5  
Pi+ not open to the sky.]

bc  read them all he thinks.


p.s. I've instructed Gate Keeper Seese on this with his handy dandy  
IR thermometer pointed at the clear sky away from the sun and at night.



On 2009, May 27, , at 18:43, John Mallinckrodt wrote:

> I've noticed that a lot of people seem to be uncomfortable with that
> explanation despite its fundamental correctness.  Of course, it's not
> completely correct because the atmosphere is not completely
> transparent.  Indeed, on cloud covered nights the sky is basically
> opaque and, as a result, radiative loss to the sky is not as big an
> effect.  (More correctly, while radiation to the sky is just as big
> an effect, depending only on the temperature of the radiating object,
> it is countered by massively larger radiative input from the clouds
> above at temperatures > 273 K rather than the piddling input from
> deep space at 3 K.)  Moreover, there are lots of competing and
> complicating processes including convection in the air, conduction
> both to the air and through supports to the ground, and radiative
> coupling to something like the 2 pi steradians that aren't open
> "sky."  As a result the effect isn't always so apparent.  But most
> people do know that, in midwinter, clear skies make for much colder
> nights.