🚀 go-pugleaf

In article <24724@dog.ee.lbl.gov> sichase@csa2.lbl.gov writes:
>In article <1992Jul20.091322.13842@vax5.cit.cornell.edu>, cpyy@vax5.cit.cornell.edu writes...
>> 
>>I understand how a single prism refracts white light to form a rainbow.
>>Could someone explain the nature of a true (Noah's Arc type) rainbow,
>>as formed by rain?  In particular, I am interested in a full description

It is important that you know that the rainbow is not produced by 
refraction of light as in a prism.  The prism effect only produces the 
dispersion of color across the bow.  The bow would appear anyway (as a 
bright white band) if there were no dispersion of colors in water.  A 
rainbow occurs because light rays are reflected inside the water drops 
in such a way that many different incident angles lead to common exit 
angle.  In effect, light rays "pile up" at the angle of a rainbow. 

There are secondary and tertiary bows, plus additional structures 
between the bows.  There is also the effect known as the "glory" that 
occurs near 180 degrees and can sometimes be seen quite clearly from 
an airliner.  My favorite is when the glory around the aircraft shadow 
appears to be leaving a mark on the clouds, an illusion produced by 
the shadow of the contrail following the plane. 

>Please run, *do not walk*, to the nearest bookstore and purchase the
>latest issue of Sky & Telescope, which happens to feature much simple
>discussion and some beautiful photography of rainbows and their variations.

Thanks for the pointer.  An article also appeared in Scientific American 
about a decade ago, and had the virtue of discussing the supernumerary 
arcs and the development of Airy functions to solve the rainbow problem, 
which had reappeared in heavy-ion scattering theory in nuclear physics 
at about that time. 

--
J. A. Carr                                    |  "The New Frontier of which I  
jac@gw.scri.fsu.edu                           |  speak is not a set of promises
Florida State University  B-186               |  -- it is a set of challenges."
Supercomputer Computations Research Institute |   John F. Kennedy (15 July 60)