As promised, I have one more post from my recent research trip to Vienna, Austria. First, a confession which will act as a bit of a spoiler, I had never heard of supernumerary rainbows until Dr. Leary joined the College and used a picture of one he had seen in Poland on his web page. Ever since then, I have been jealous and longing to see one myself.
One Sunday when I was in Austria, my host Dr. Smoliner and his wife and I went on an excursion east of Vienna to Schloss Hof, a palace built by Prince Eugene of Savoy in the 1720s and later renovated by Empress Maria Theresa. I love visiting these types of palaces — not just for the buildings themselves but especially for the gardens.
It was raining on and off, so we went to see the gardens first, and got caught in the rain. After drying off a bit, we went through the rooms, which mainly had their window shutters closed to protect the furniture and wall-coverings from sunlight. As we reached the room in the front corner of the building, the shutters were open to allow views of the Baroque gardens. I looked out the window to the side of the Schloss and gasped in surprise — out the window was a supernumerary rainbow!
The supernumerary part of a supernumerary rainbow is the extra fringes that you can see on the inside part of the bow. Most of the colors are washed out in the fainter bow, but you can generally see the extra greenish/purple lines. In my picture, you can mostly just see one extra light green line, especially toward the top of the bow. You get supernumerary rainbows when the rain droplets are particularly uniform in size.
The sky cleared quickly while we were looking at the rainbow, so our timing was so very lucky! Here’s the view directly to the front of the Schloss just a moment later. By the way, the large hill you can see is actually in Slovakia! The border is a river which you can kind of see in the picture as the line of trees that follow the river.
So, we left Schloss Hof and headed toward a national park on the Danube, because I wanted to see the wetlands (the Auen) around the river. As we drove, another rainbow appeared and became so bright and vivid that we had to pull off the road to get a picture.
Everybody on the road was stopping, it was so amazing. A nice Austrian man tried to tell me something that my German was not quite up to at first, but then I realized he was saying the rainbow was so close that you could see that it was in front of the trees at the back of the field. That is, if you enlarge this picture (just click on it), and look at where the rainbow appears to meet the ground, you can see that the trees are behind the rainbow. Totally awesome. And, it’s another supernumerary! Look towards the top of the bow to see the extra fringes. Apparently, Thomas Young used the existence of supernumerary rainbows as part of his argument that light was a wave. The extra fringes cannot be explained by ray optics — you need interference effects.
Finally, we wrapped up the sight-seeing at the Donau-auen park, and the light of the late evening sun was just beautiful. Sunshine on the water looks so lovely….
That’s the beautiful blue Danube! Again, you should click on this image to make it full size. You should even be able to spot the moon, in the middle of that amazing sky.
We wrapped off the day with a good meal and conversation at a very traditional Wiener heurige at the edge of the Wiener Wald. It was definitely one of those tremendous days to keep in your memory to cheer you up when things are darker. When I’m scraping the ice off my windshield this winter, I can just go back in my mind to Schloss Hof and my two supernumerary rainbows!