A few days ago, we had a perfect rainbow in our backyard. It started to form a second rainbow, but it did not completely form before fading away.  The thought then crossed my mind, “Why are rainbows curved?”  It has been a long, frustrating journey but I now have an elementary understanding of why rainbows are curved.
First off, you have to realize that all rainbows are complete circles. We only see half of the rainbow because the horizon blocks the other half.  The only way to see the complete circle is from a very high location, like being in an airplane.  
Secondly, the water droplets act like little prisms reflecting the sunlight at a 42-degree angle. The other problem we have, is not thinking of the rainbow as a three-dimensional creation.  This causes the geometry of the cone of reflection to appear as a giant bow.  Don’t forget we are only seeing a little over half of the complete circle of the rainbow.  
If you imagine one of those giant cones that cheerleaders scream through, your eyes would be the mouth piece, and the large end would represent the rainbow.  If you tilted the cone over a table, at a 42-degree angle, you can get a real good idea of what is going on when we see a rainbow. 
I unofficially declare Florida not only as the lightning capitol of the world, but also, as the rainbow capitol of the world. I have seen more rainbows in three years, then I have seen in my entire life.   
One more thing that I never realized is that the visible light prism we see contains seven different colors.  As I am sure you probably know, seven is the Biblical number for perfection, and completion.  I find it more than coincidental that we have seven colors in the light prism.  It would be hard to argue that it is not perfectly complete.  An easy way to remember them is by memorizing the name ROY-G-BIV:  R-red, O-orange, Y-yellow, G-green, B-blue, I-indigo, V-violet. I hope this gives you something to help you appreciate your next rainbow a little more. 

 God bless you all, 
RHM