Natural tertiary rainbow 3rd order
On May 15, 2011, a rain area moved from north to south. When it started to rain at my position, I immediately rushed to my observing site which is reachable within 2 minutes for me.
Once there, I saw beautiful specimen of the primary and secondary rainbow. During my observation, the rain intensified, and now I knew hat I had to look for!
On the left side of the sun there was a relatively dark cloud bank providing ideal conditions for a possible sighting of the 3rd order rainbow.
In fact, I had the idea of seeing a very faint arc at the expected position of about 40° away from the sun. It is really exaggerated to say that I saw it, but there seemed to be something.
I went into the shadow of a tree in order not to be blinded by the sun.
Now I did not take any care to protect the camera from the rain, I just had a little box with me to put the camera into. The arc could not be seen for more than 30 seconds, but I´m sure there was something at that position.
As under those lighting conditions a correct exposure is hard to get, I took my photographs in RAW mode. All the “little helpers” of the camera had to be set off.
To my disappointment, I did not find anything at the expected position when examining my pictures on the PC screen. But when putting an unsharp mask over the pictures, I saw it immediately. A bow! You can see that the outer part of the bow is slightly red and the inner part is light green.
Here is an animation showing the original image and three different settings: Unsharp mask, intensified colours and inverted.
If you need more information about the measurements of this tertiary rainbow, take a look at this pdf-file written by Dr.Alexander Haußmann. Thank you very much for your calculation!
Author: Michael Großmann, Kämpfelbach, Germany