[Phys-L] Re: Rime on the Windshield

[Bernard Cleyet <bernardcleyet@REDSHIFT.COM>]

We see this often here in Salinas.  When the car is parked on the
street, sometimes the side windows ice, more often dew, but not in the
driveway where the car is sided by a brick wall and the house.  The
front and rear windows, of course, ice or dew.  When a telescope dews,
one aims it at the warm, relatively, earth for a short time.  I also use
a hair dryer.  This is, as LP pointed out, more important for the
corrector plate, as the mirror has the double duty support and dew
shield.  Some telescopes have an open frame so the mirror will cool more
quickly.  My dew shield (LP's solid angle) is black foam -- home made.

BTW, numbers may be attached to these effects by using the cheapie IR
thermometer from R/S or the more pricey one from Costco -- someone on
this list discussed the more expensive one.

bc, who thinks amateur astronomers learn Physics in addition to Astron.

p.s. the effectiveness of mulch is shown by the frost on the mulch
covering our left what would be a lawn  persimmon tree only in middle)
and the grass just dewed.   Our new high tech. (and expensive) millgards
now dew on the outside instead of the inside!

Leigh Palmer wrote:

> The truck's windshield probably slopes so that the sky subtends a large
> solid angle at smaller angles of incidence. The clear sky is quite cold,
> and glass is nearly black in IR. The air temperature was probably above
> freezing, but the windshield was colder than the air. Water condensed on
> the windshield and froze. The other windows "saw" a higher radiation
> temperature environment and thus did not get cold enough to accumulate
> ice.
>
> Here in colder country we see this phenomenon often when the temperature
> is above zero. It is also a major annoyance when using a telescope with
> a front optic. We don't have to worry about it lately however; it has
> been raining for more than three weeks here. Carports are quite
> effective in preventing windshield icing.
>
> Leigh (a recovering Californian)
>
> On 13-Jan-06, Brian Whatcott wrote:
>
>
>
> > It was warm out yesterday, but the sky was clear last night, and by
> > today's early light, there was a light coat of ice on my truck
> > windshield
> > - but only the windshield, but not either of the side windows or
> > the rear window.
> > The truck was facing south east, into a sailboat, and was sheltered
> > by the house front too. It's a black '94 GMC truck. The prevailing
> > winds are either south which is warm, or north which is cool.
> >   I think I know why it iced that way - can you guess?
_______________________________________________
Phys-L mailing list
Phys-L@electron.physics.buffalo.edu
https://www.physics.buffalo.edu/mailman/listinfo/phys-l