🚀 go-pugleaf

In article <2A6DEF17.1804@ics.uci.edu> bvickers@valentine.ics.uci.edu  
(Brett J. Vickers) writes:
> peterk@public.sub.org (Peter Kittel) writes:
> >Is it only me or does the sky beneath a rainbow also appear lighter
> >to others than the sky above a rainbow (or wait, was it the other way
> >around?)?
 
> Optical illusion?  Two fields of the same color, separated by a line
> of a brighter or darker color, give the optical illusion that one half
> is lighter than the other.  The trick is to cover the line and see that
> they are the same.  I've never tried this with a rainbow.

Not an optical illusion. Above the primary bow of the rainbow is  
Alexander's dark band, first 
described by a philosopher Alexander [not the Great] in Hellenistic times.
There's a  Scientific American reprint volume on atmospheric optics which
explains this and other features of the rainbow (I don't have the  
reference handy.) There's also a Dover book "The nature of light and 
colour in the open air" (approx. title); I've never seen it but it's  
probably a good place to look for information on atmospheric optics.  

--
Geoffrey Mess
Department of Mathematics, UCLA
Los Angeles, CA.
geoff@math.ucla.edu
NeXTmail welcome.