Re: ATM Aluminum Dew

[Robert Duvall <rduvall@pixworks.com>]

Jack Schmidling wrote:

> However, when not in use, I store it in an unheated building with open
> windows where the temperature and air/humidity is essentially the same
> as outside.  The mirror goes through the same temperature cycle, is
> exposed to the same humidity but never dews up.  Well, almost never.  The
> last time I brought it in (in the afternoon) it dewed up the next day
> but never again.
> 
> How come?

If it's in an enclosed building (especially wood), the radiative cooling
is much slower than the open sky. This means it will not cool as rapidly
and thus may not go below the dew point in that situation. The sky is an
ideal blackbody and thermodynamics say that that you'll get alot of
radiative cooling when your scope is outdoors. Hope this helps.