Rainbow god circle

[Tod Mahony]

John M. asks:
> (3)  Along these lines, didn't I learn way
> back in grade school that what we call a
> rainbow's arc is only half the rainbow?
> Don't rainbows continue, under the Earth
> as it were, and eventually join up into a full
> circle?  Isn't the parabola of a rainbow
> actually a perfect semi-circle and not  the
> often-assumed bell-shaped curve?  If we
> could--pick up--the rainbow and project it
> onto the sky, wouldn't it be a perfect
> circle?  So half of every rainbow is missing,
> an absent presence, and the--real--
> rainbow meets itself like Kekule's serpent,
> only we can't see that because of the
> horizons.

This is from the Earth & Sky radio show
archives -- check out their web site at
http://www.earthsky.com/ --

 "Friday, March 15, 1996

 DB: This is Earth & Sky for Friday, March 15.
 When sunlight and raindrops combine to make a
 rainbow, they can make a whole circle of light
 in the sky.

 JB: Sky conditions have to be just right for
 this, but even if they are -- when viewed from
 most places on Earth's surface -- the bottom
 part of a full-circle rainbow is blocked by
 your horizon. And so we see rainbows not as
 circles but as arcs in our sky. When you see a
 rainbow, notice the height of the sun. It helps
 determine how much of an arc you'll see -- the
 lower the sun, the higher the top of the rainbow.
 But if you could get up high enough, you'd see
 that some rainbows continue below the horizon.
 Mountain climbers sometimes see more of a full-
 circle rainbow -- though even a high mountain
 isn't high enough to show you the whole circle.
   

 DB: Pilots do sometimes report seeing genuine
 full-circle rainbows. They'd be tough to see out
 the small windows we passengers look through --
 but pilots have a much better view."