Re: Sunsets

[brian whatcott <inet@INTELLISYS.NET>]

At 13:13 8/30/00 -0700, Leigh wrote:
> ... sometimes I see sunsets which are not red in relatively
> clean air. A red sunset, while not uncommon, sometimes is not
> seen, even when the atmosphere is present. I conclude that the
> air alone cannot produce a red sunset.
>
> Leigh

Yes.
While all the fully paid up physics savants manfully, (even
womanfully) resist drawing such a straight forward conclusion
 from the facts presented here, a physics philatelist need have
no such scruples.

1) Dusty skies tend to produce vivid red sunset skies.
2) Clear air tends to provide no such shepherd's/sailor's delight.
3) Rayleigh, Thompson, Einstein, Uncle Tom Cobbley an' all tend to
support the idea that chromatic scatter depends on physical features
less than 30 nm in size. These features may be atomic, molecular,
 or thermodynamic.
4) Dust particles have mean sizes much larger than 600 nm.
Tyndall territory.

      So where's the *chromatic* scattering source?

Answer: Where there is a recognizable population of large particles
(scattering *white* light), there is also a concomitant tail of small
particles, fellow travellers as it were who if not exactly communist,
have a reddening effect.
 A population of this kind, over a long path length, both dims the
sunset, and reddens it.

Of course.
 I hereby call this effect, "Whatcott scattering".
You're welcome.



brian whatcott <inet@intellisys.net>  Altus OK
                Eureka!