Blog Archives

Distorted Solar Disk by Smokestack Exhausts


The Hungarian observers Attila Kovács and György Répás witnessed an unusual kind of refraction. The temperatures in the exhausts of smokestacks differ widely within a small space, which causes very bizarre distortions of the sun.

Attila reports that such strangely distorted solar disks can be seen almost every day in the exhausts of smokestacks. So it is worth while trying it by yourself to get a live impressions of physics.

   Attila Kovács at the hospital of Eger, November 11, 2014:
   György Répás, smokestack in Budapest, March 29, 2014:

Fraunhofer lines in rainbow ?

Fraunhofer lines are dark lines in the sun’s spectrum. They are caused by resonant atomic absorption of the sun’s thermal continuum radiation by photospheric gases.

The lines provide clues to the chemical composition of the solar atmosphere, as well as its physical conditions like temperature, pressure, magnetic fields etc.

My rainbow photography dated 11.Oct.2013 showed some greyish bands in the yellow.

Are they traces of the strongest Fraunhofer lines or artifacts of the camera’s sensor being unable to profile intermediate colors?
Is it possible at all to obtain spectral lines in nature without a prism or grating?

Author: Michael Großmann, Kämpfelbach, Germany

Third and Fourth Order rainbow in Russia

Sergei Antipov observed on June 22, 2013 in the Vladimir region, Russia (100km from Nizhny Novgorod city) beside a primary and secondary rainbow, the rainbow third and fourth order too.

Time: 14:00 (UTC + 4h)

Weather condition:
+20.1ºС, relative humidity 98%
atmospheric pressure 747mmHg (normal at 82m is 752-753mmHg)
Min/Max: +14.0º / +20.8º
Rain during the day: 3 times, thunder-storm and heavy rain.
wind: in the morning northern, in the afternoon and in the evening eastern
Light breeze, 1 – 3 meter per second, gusts were not stronger than 10 meters per second

Photo time with 1st and 2nd order rainbows: 19:37 (+4)
Photo time with 3rd and 4th order rainbows: 19:47 (+4) (1st, 2nd were visible too)
sunset: 21:52 (+4), azimuth 315º
sun azimuth @ 19:47 291º, height 15º

In late afternoon there were black clouds that came from the east (usually cumulonimbus comes from the west). Cumulonimbus covered almost all the sky and although it was not raining, there was a bright primary and a good secondary rainbow. The sun was covered by clouds. You can see that on a roof of the house there is no shadow. But two rainbows were visible and were bright!
10 minutes later there was bright sunshine (you can see a shadow on a roof of the house).
The sun appeared at 19:47. Till this time the sun was hidden).
The rain began at about 19:45. 3rd and 4th rainbows are photographed from under an umbrella.
But the rain was very weak. From the sky rare droplets of water fell.
Even the roof of the house remained dry (but with traces of drops).
At this moment the rare rainbow also was observed.
The heavy rain began much later (>20:00)
The sun became covered by a cloud, and the first rainbow gradually disappeared.


  • Good weather (the last hour)
  • clouds (from the East) and sun (in the west) ~ 19:00
  • dark clouds (sky half) and sun ~ 19:20
  • gray clouds (3/4 of sky) and NO sun, No rain (Or very slight rain that I didn’t feel it) = 19:37
  • Beginning of observation of the first rainbow (without rain and without sunshine) within a few minutes there was a sunshine
  • very dark clouds (more, than 3/4 of sky) and bright sunshine (the sun shone from beneath a cloud border)
  • Slight rain (isolated droplets)
  • photo of observation of 3rd rainbow at 19:47

The panorama is made of two photos with an interval 10 minutes; photos are made from different places (about 10 meters). The lens has a bad distortion towards the edge…

Weather that evening was unusual. Cumulonimbus clouds came from the East (usually they come from the West). Therefore I well remember that evening.

The Quality of the original photo is not really good therefore all colors of a rainbow are visible only on “psuedo-HDR” processing (combination of 15 files from one raw with different parameters of brightness, contrast, an exposition and a saturation (12).

From one file it is difficult to receive such picture: red color smoothly passes in green color without orange, without the yellow (edited photo).

Each method of processing has the merits and demerits. For example, processing in the LAB mode very well showed 4th order, but a bad color rendition of 3rd order rainbow.
Processing with imaginary hdr shows 4th worse, but much better color at 3rd order rainbow.

This sketch show the most interesting moment.

My 3rd and 4th order rainbows are very similar to rainbows of Michael Theusner: strictly at level (at height) the sun, rainbows seem vertical. From below and from above, rainbows sharply are rounded. This effect (I think) is explained by that rainbows have the best brightness at sun height. Very much reminds ice halo: at it too (very often) the brightest piece at the left and to the right of the sun.

Nicolas Lefaudeux invented a search method 3rd order rainbow. His method is outlined here and given in more detail.

I used an other (own) method. It is a Processing scheme to find a rainbow in the photo from one 16bit tiff file from RAW (in LAB mode in Photoshop):
RAW file -> Lightroom3 -> zeroed preset -> 16bit tiff file -> Photoshop -> LABmode

I don’t think that my Processing scheme can be suitable for all photos of other photographers.
But, this method very well shows rainbows in my photo (Frankly speaking, I couldn’t repeat Nikolos’s method – I am the novice user of photoshop 🙂 ).
For faint Rainbows it is necessary to work with layers of A and B (in LAB mode).
You can see a layer “L” on this picture and here the result of work with use of my method.

Author: Sergei Antipov, Russia

Related Post: Natural tertiary rainbow 3rd order

“Spektrodrom” – A Laboratory of Rainbow

The simulation of rainbows of many orders with hanging or standing water drops and laser light is straightforward, but often unrealistic due to deformation of the drops. Therefore, a modern version of Billet’s experiments was designed, which uses a laminar cylindrical flow of water, and white light by just a few pixels of a video projector. It is surrounded by a circular projection screen. Using slightly skewed rays, which are therefore “climbing” up the cylindrical beam of water and exiting from it in proportion to the number of partial reflections, is able to produce a simultaneous display of the first six rainbow orders in white light.

The 2nd and 3rd order.

The 1st, 4th and 5th order.

The first 4 orders.

Both 1st and 2nd orders.

Both 3rd and 4th orders.

The first six orders.

Animation about the different refraction angle beetween salty water and fresh water.

Author: Michael Großmann, Kämpfelbach, Germany

Deformed Glory

Matěj Grék placed a strong halogen lamp somewhere around 20m away and take some photos from a fogbow. He noticed that the glory was deformed. The wind was strong in this night, the fog was moving quite fast, and with the fog of course also tiny water droplets. Maybe that’s why the glory is deformed in connection with divergent light. Images are taken with a polarization filter.

Camera: Nikon D60; F/6,3; f/30mm; t=30sec. at ISO 200

Author: Matěj Grék & Michael Großmann, Kämpfelbach, Germany

Colours in Citric Acid

Lately I experiment a lot with crystal growing and I knew that Citric Acid can refract the light, but when I saw this I was more than surprised. These flat crystals of about 1-2 cm in diameter (the larger ones) were grown between two glass plates, then put in front of a polarized light source and photographed with a polarization filter. It took a few tries to find a proper way to grow them flat enough for this purpose though. More Photos see here and here.

Author: Rolf Kohl, Germany


Dew bows are a kind of rainbows. The difference lies in the plane of projection and in the fact that static droplets are reflecting the refracted light back into the eyes of the observer. The rainbow cone resulting, the apex of which is the oberver´s eye, is cut by the plane (the field). The result is a hyperbola, but for our eyes, there is always a circle!.

The first nights in October were rather cold, so that a lot of dew could form in the fields.

I knew that the following days were ideal for looking for the dew bow.

The main problem while observing dew bows is the brightness of the field. A polarization filter makes the dew bow contrast better from the background. (2)

An even better idea was filming the dew bow while driving along the farm track. This makes it contrast even more clearly.

Place : Neulingen, Germany
Time : 02 October 2011
DSLR Camera : Canon EOS 450d
Exposure : 1/25 sec, f/10mm, F/7, ISO 100

Author: Michael Großmann, Kämpfelbach, Germany

A single water drop

A slight-projector and a singel water drop shows a lot of bows. Here you can see the primary, secondary and tertiary bow.

The distance between the water drop an the projection backside (white paper) is 30 mm, waterdrop an light source has an diameter of 2 mm.

Photo taken on 28.07.2011 on my desktop 🙂

Author: Michael Großmann, Kämpfelbach, Germany

Double dewbow

On June 25, 2010, Rüdiger Manig observed a double dew bow on unevenly spread morning dew on a leaf in Neuhaus am Rennweg (Thuringia, Germany).

Especially when he slightly defocussed his camera, the bow could be distinguished better.(123)

Actually, the distance between the two bows was less than 10°, the angle which one could expect in a double dew bow. Maybe, however, that the angle of refraction was significantly reduced by the deformation of the droplets on the leaf.

3rd and 4th order rainbows

Last evening (11 June 2011) thunderstorms approached my home town Schiffdorf near Bremerhaven in Northern Germany. I went to a field road by car to take some photos of the storm clouds. Just after I had arrived (about 18:00 UTC), heavy rain started which lasted for nearly 20 minutes. To my disappointment, the rain covered the gust front and most of the interesting features of the storm. So I waited and hoped that the sun would come out soon and produce some nice rainbows. When it did I realized that the dark clouds covered the sky to the right of the Sun – just the situation Michael Großmann had had when he took the the first image of a 3rd order rainbow only four weeks ago. I decided to try this out as well. Instead of one image I took sequences of five to stack them and, thus, increase the signal-to-noise ratio. I hoped this would increase my chances to detect the 3rd order bow. I took the images from my car through the open window to protect my camera (Canon 40D) from the rain. Visually, I did not see a 3rd order rainbow. However, in my back, the 1st and 2nd order bow developed nicely.

Back home I converted the raw images to 16-bit-Tiff and stacked them in Photoshop. Adjusting saturation already showed the 3rd order bow in the image sequences taken between 18:17 and 18:22 UTC (first image).  Applying unsharp masking revealed something unexpected in one of the stacked images (from 18:19 UTC): There seemed to be another rainbow close to the 3rd order bow, but, with reversed colors (second image). I checked Les Cowley’s website and realized that my image likely showed the 4th order rainbow!

After some more sophisticated processing including denoising (Neat Image), unsharp masking and increasing saturation, the 3rd and 4th order rainbows both were clearly visible. Finally, I created a composite using masks to retain the natural look of the foreground while still showing the 3rd and 4th order rainbows (third image).

Author:  Michael Theusner, Bremerhaven, Germany