I'm having trouble locating by Big Book of Physics, which
means I'll have to do this from memory. Get out your copy of
_Dark Side of the Moon_ by Pink Floyd for a visual aid.

First the basics (which you probably already know). White
light is a mixture of many wavelengths electro-magnetic radiation
propagated by the quantum dance of electrons as they are goosed
from one energy level to another by changes in available energy.

Each of these wavelengths moves at 300 000 000 meters/second
in a vacuum (and pretty close to that in air). Their various
wavelengths have corresponding frequencies. When these wave hit
an optically dense medium like water or glass, their wavelength is
shortened, but their frequency remains the same and speed must change.
To keep the relationship between frequency, wavelength and speed,
the different wavelengths have different speeds in the more optically
dense matter and the colors spread out. This spreading out
bends the path of the light (differently for different colors)...
they are refracted.

Here's the tricky part. When leaving an optically dense
medium they are bent back toward their original path, but if the
object through which they have passed is round or triangular
(pretty much anything other than rectangular), the angle of
refraction is too great and the light is reflected instead, still
separated, toward the light source (or pretty close). This
produces the standard rainbow (blue on top). In a raindrop, the light is
refracted and separated on the way in and reflected off the back
surface of the drop. To see a rainbow, the observer must be
between the light source and the water droplets.

The secondary rainbow requires a very bright day, a very
precise light source, observer, droplet orientation and really
clear air. Two internal reflections are necessary inside the
droplet and much of the energy is lost through scattering and
absorption. The first reflection reverses the order of the
colors the order putting blue on the top (if you check your Pink
Floyd album red should be on top.) The second bounce inside the
raindrop flips the color sequence again.




>
>Can anyone explain to me why the secondary rainbow (the fainter one outside
>the main one) is a mirror image of the main rainbow. That is, the color
>sequence is reversed.
>Reply to me personally if you like.
>Stan Ray
>STAN RAY
>
>
>

--
*********************************** I got the blues so bad one time
* Mike Patterson, Astoria, OR * it put my face in a permanent frown
* mpatters at orednet.org * but I am feelin' so much better
*http://www.pacifier.com/~mpatters* I could cake-walk into town