Nice topic,

My understanding is that it is a perfect semi-circular arc, the second or concentric are would also be a perfect circle too.

What I haven't been able to figure out yet is placing myself in the correct position, between sun and rain to catch such an amazing image.

Any direction much appreciated.

I don't mean to be turning 'gauchinver's query into somthing different

Ed,

Thanks for the info and the link, now all I have to do is put it to practice!!

Thanks again

Well DrSloy.. I really like that one.. Majoring in Visual Art at uni, I found it very interesting to learn how colour is created, or viewed.. Each colour is made up from an equal mix of the colours either side of it.. All rainbows have the same colours.. We only see colours in the RGB rang equivalent.. Our brain cannot see more than that in nature. There are other colour spectrums we cannot even see within a rainbow with our eyes..

Now here is a thing.. A scientist told me many years ago that what we see is the colour created from the right angle of view.. The rainbow is floating on top of a bubble .. What we are seeing is the edge of that bubble.. A bubble can be an entire sphere which I have seen around the sun.. Now that was an amazing rainbow.. Very clear and a lot smaller than the normal rainbow.. Now, why curved.. Its the way of things.. Its gravity.. Its a natural shape created by the forces of nature and physics. The same scientist told me that the bubbles are everywhere but we cannot see them. They are often called Clear Air, sometimes aircraft fly into them and drop. She said she thinks they are bubble of natural occurring pure Hydrogen  which rarely appear in a pure form on Earth but in fact its the most abundant gas in the universe. She said, think of it as a bubble you make with a bubble mix.. You can see a rainbow in it.. A nature rainbow is the same thing... Fine water mist droplets show the edge of the Hydrogen bubble creating a rainbow. Some bubble mix bubbles lay on the ground as only part of a sphere too.. The scientist is my grandmother, she has a PhD in physics. She loves this rainbow too..

Science geek
Destiny...

To Destiny:

The shape of a rainbow is not due to gravity : its a pure matter of geometry. Would you be in a plane and watch a rainbow, you would have a complete circle.

Please, go to http://en.wikipedia.org/wiki/Rainbow to have the complete explanation about rainbows and even see a full circular one.

Light is electromagnetic wave. Each color has its own wavelength. The visible spectrum ranges from 0.4 to 0.8 Microns wavelength. Then, you have the infrared on one side of the visible spectrum and the ultraviolet on the other side. They can not be seen by human eyes, but they exist : the ultraviolet light can burn our skin! and both can be measured... by dedicated optical systems.

You could even modify your camera (by removing the infrared filter) to shoot infrared pictures : a little strange, very nice.