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


Posted on June 1, 2011, in observations, rainbow and fogbow and tagged , , , , . Bookmark the permalink. 17 Comments.

  1. If a phenomena is predicted mathematically there must be someone to observe it – well, it was worth while waiting so much! Congratulations!!!

  2. Elmar Schmidt

    Hats off, Michael!

    Although the last bit of geometrical evidence still must be corroborated, I cannot think of something else than said tertiary rainbow from a diligent person like you.

    You worked so hard for it and have well deserved this atmospheric optics feat of the century!



  3. Congratulations, Michael,
    This is a wonderful observation. Is there any possibility of calibrating the image in terms of angle and verifying the angle of the observed bow? I’m convinced, however.
    Alan Clark

  4. Patrik Trncak

    Hi Michael,
    why ONE photo only? Where are photos of primary and secondary bows? Know you Registax for stacking?

  5. Hello Patrik,

    If you want to see the other both bows, take a look in the text, i have insert a link.
    But you know that the tertiary rainbow arises in sun direction and can not be found in the direction of the primary and secondary rainbow. In this direction i hope to find someday the 5th order 🙂

    Registax I know, but I think a picture should be recognizable as such under real conditions.

    Best regards

  6. Michael Großmann

    I’ve forgotten to mention yet, a tertiary rainbow form may also occur alone. It must not rain in the area of the antisolarpoint.


    I think it’s a milestone in the rainbow theory that’s possible to observe the tertiary rainbow in nature … without stack and without another tricks.

  8. Elmar Schmidt

    A first try at registering Michael’s tertiary with a starfield photograph from which to obtain azimuth and elevation data, gave (41,3 +/- 0,6) degrees for the radius of the bright reddish part of the bow. This is in very good agreement with the theoretical radius prediction of 41,9-42 degrees, which is valid for the very red end (650 nm) of the rainbow’s spectrum, and thus vindicates this spectacular achievement.

    Still amazed!


  9. Thanks a lot for publish of measurements. I hope this remove all doubts.

    Best wishes

  10. Hi Michael

    I found out about your research on the BBC News website. It caught my attention because I adore rainbows. I took many pictures on 17 September of the most beautiful rainbow I have ever seen in my life. The reason I’m writing this is because I’m not a scientist and am a bit confused about what a tertiary rainbow actually is.

    What I saw, very easily with my eyes, and which is also in my photos (with the help of some heavy unsharp masking), was the main rainbow, with another some distance above it, with the colours running in the opposite direction. Then, underneath the main rainbow were four further rainbows (and maybe even the hint of a fifth – or more!), each getting fainter than the last. Is this a tertiary rainbow, or are you talking about something else? I did look at your animation, but I’m not sure what I was supposed to be seeing. Would much appreciate your feedback. I can send you pictures if you’re interested. Thanks…


  11. Hmmm… I think you’re talking about something completely different – so apologies for my ignorant post!


  12. Michael Großmann

    Hello Jane,

    thanks for your comment. And sure this is NO ignorant post from you:)
    Thats what you´ve seen is the secondary bow above the primary. And the bows inside of the primary are supernumary bow.
    To find a tertiary rainbow you must look to sun direction.

    Please send me the picture from the rainbow, i´m interested! And if you have any questions….you´re welcome 🙂



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