Category Archives: miscellaneous phenomena

Circular Wing Tip Trails

During a helicopter operation at Mt. Wendelstein on September 9, 2011 in very moist air, Harald Jauernig observed that the rotor blades of the helicopter caused condensation of the moisture.

This phenomenon is called wing tip trails and is caused by the difference of pressure between the lower and the upper part of plane wings. The air passing above the wing moves faster and so has less pressure than the air passing below the wing, causing an updraft which lifts the plane. This is what makes airplanes fly.

When pressure drops, the air cools down, so that moisture can condensate and form droplets or even ice crystals when it is cold enough. These become visible as a thin stripe of cloud extending backwards from the wing tips (wing tip trails).

In this case the wing tip trails are forming circles because the rotor blades of the helicopter rotate.

More pictures: 1234

Authors: Claudia Hinz and Peter Krämer

Rings of Quételet

Rings of Quételet are caused by rays of light which had been scattered by particles of dirt on a window pane and then were reflected from the rear side of the pane, interfering with rays having been reflected from the front side of the pane and then having been scattered by the same dirt particles.

The light source itself forms a white circle being surrounded by colourful rings which are caused by interferences.

These rings always begin with a blue one right outside the white circle and end up with a red one on the other side, away from the circle, no matter if the secuence begins in the centre of the pane or on its rim.

Place : Fehraltorf, Switzerland
Time : 24 August 2011
Digital Camera : Canon EOS 450D
Exposure time : 1/2500 sec , f/9 ,Focus length 22mm, ISO 100

Author: Michael Großmann, Kämpfelbach, Germany

Colourful flies leg

Since a short time I ever and again go down into the microcosm, a very interesting and colourful world. A lot of optical phenomena in the sky can also be found in this little world. The origin of the colours are usually diffraction and interference. Actually it´s no wonder, that these tiny structures are able to bend the light. So it´s probably possible that the bristles of a flies leg get colourful. Well, I think, I should analyze the hairs on my legs, too.. . 😉

The compound eye shows interesting effects as well and the wings anyway. Some flies have seemingly a gold foil between the eyes.

More pictures of my journey into the microcosm can be found here: – 12345

Author: Sven Aulenberg, Saarburg, Germany

Goat Willow Seed Corona

Around noon on April 22, 2011 (Good Friday), I went to a hedge near Limburg (Hesse, Germany). As the weather was sunny and dry, some goat willows (Salix caprea) sent a large amount of seeds into the spring air. Together with the bright mid day sunshine, these caused some surprising effects. Often there was just one bright area around the sun (123), but from time to time a colourful corona appeared in the seeds.

Author: Gerrit Rudolph, Hesse, Germany

Bird Feather Iridescence

While taking a walk through the surroundings of my home on February 20, 2010, I took the most of the nice weather by taking some last winter photographs. At 10:09:27 CET, a small covey of about 15 siskins (Carduelis spinus) flew off an alder in front of me and passed me to the right. Seen from my position, they directly passed in front of the sun. I took some photographs with my Sony DSLR-A 700 and a Minolta lens 4/300 mm. The exposure time was 1/8000 second at an aperture of 32 and ISO 200.

Further settings of the camera were: Programme, serial photographs, automatic white balancing, and integral measurement stressed on the centre of the picture. In the original photograph, the sun is almost at the centre of the photograph. The precedent image of the series was exposed for about 1/4000 second at an aperture of 16.

That picture is brighter (a small part of the sun can be seen at the right rim of the photograph!) and the iridescence in the feathers looks rather faint.

Author: Rene Winter, Eschenbergen, Germany

“Bubble Bow”

This picture actually shows just a few air bubbles frozen in a sheet of ice. But when watching it from a certain angle against the antisolar point, I discovered these strange colours. These can be expressed as a kind of “inverted rainbow”, as the circumstances under which it formed are exactly reversed to those of a normal rainbow. In a rainbow, the spherical object consists of water, but in this “bubble bow” the spherical object consists of air.

But there is a crucial difference: The ordinary main rainbow is based upon a double refraction of light and one inner reflection. But in case of this “bubble bow” the light is refracted four times: When it enters the ice, it gets refracted for the first time. The second time is when it enters the bubble. Then it is reflected once (or several times?) inside the bubble before it gets refracted a third time when leaving the bubble and entering the ice again. Finally, it gets refracted a fourth time when it leaves the ice. The “bubble bow” formed by this procedure has the same sequence of colours as a normal rainbow. But I do not know if it can ever be seen as a whole.

Photograph taken in Barsinghausen-Egestorf (Germany) on March 5, 2010, with a Canon EOS 1000d camera. More pictures are here.

Author: Reinhard Nitze, Barsinghausen, Germany

Iridescent Fireworks Smoke

Like everywhere around the world, New Years Day was also welcomed with fireworks around Mt. Wendelstein. It is always a special highlight to watch the fireworks from the top of the mountain at 1838 meters above sea level. In the Leitzach Valley, about 1000 meters lower, there was a fireworks display.

Even when watching it with the naked eye, the smoke and fog of the fireworks seemed to show iridescent colours. The photographs (photo) show the iridescence more obviously. It was probably caused by the condensation nuclei from the fireworks smoke, on which small droplets condensated. As short time before an area of precipitation had passed, air humidity was still very high.

Additionally, the fireworks caused a thin layer of fog over almost the whole alpine foothills area (photo), and the big city of Munich with more than a million inhabitants, was covered by a thick layer of clouds (photo).

Similar things were reported by other observers. In Bochum, Peter Krämer observed that light graupel turned into snow during the fireworks, leaving about a centimetre of snow. On the weather radar it could be seen that a precipitation area formed right over the Ruhr area just after midnight.

Two years ago, thin fog with visibilities around 300 meters thickended after the New Years Fireworks, forming a dense layer of fog with visibilities which were less than 10 meters in some places.

Posted by Claudia Hinz

Interference Phenomena on Soap Bubble Surface

Inspired by my daughter who was playing with soap bubbles, I one day got the idea to take photographs of the surface of soap bubbles.

For this purpose I filled a big dark frying pan with water and put some dishwashing liquid in it. I mounted my little digicam on a clamp pod (figure 2) and aligned it roughly with the pan.
Then I blew some bubbles into the water using a drinking straw. Now I aligned the camera exactly with the vernier adjustment of the clamp pod and started photographing.

Already the first pictures turned out well, and a short while later I had made a considerable amount of pictures. I soon noticed a remarkably large variety in the positioning of the different colours on the soap bubbles. At first, the distribution of colours on the bubbles looked like a piece of abstract art, but later the colours arranged to parallel stripes, similar to a rainbow.

The reason for this play of colours:

The physical reason for these colours is the so called two-beam interference. This is remarkably well explained at http://www.itp.uni-hannover.de/~zawischa/ITP/zweistrahl.html (German) and http://www.itp.uni-hannover.de/~zawischa/ITP/twobeams.html (English).

The main statement in this explanation is that the colours depend directly from the optical length of way (and so from the thickness) inside the the soap layer. This is an explanation as well for the black “holes” at the highest point of the bubbles, as also for the colourful rings below these “holes”. The colourful flaws, which can be seen especially on “fresh” bubbles, are areas of different thickness of the soap layer, which are (still) positioned irregularly. Following the force of gravity, they slowly flow downwards causing the soap layer to be thinner at the top and thicker at the bottom of the bubbles. The constantly the thickness of the soap layer increases from the top to the bottom of the bubbles, the more regularly is the positioning of the colourful rings.

The Picture above show a detail on the surface of a soap bubble.

Figure 2: Camera mounted on a c-clamp. The distance between the camera lens and the soap surface is here about 4 cms.

Figure 3: Abstract play of colours on the surface of fresh soap bubbles.

Figure 4: The lesser the flaws in the soap layers are, the more regular is the increase of the thickness of the soap layer towards the bottom of the bubbles, and so is the play of colours. The spotted dark areas on top of the bubbles indicate that the bubbles are about to burst.

More pictures: 567

Author: Reinhard Nitze, Barsinghausen, Germany

Intense colours of a light refraction on fireweed seeds

This year the season of my firweed-hunt began earlier than last year because in hope of a better lightrefraction on early seeds. It was about mid-july when I saw the first seeds falling and I was very surprised when i moved the seeds beetween the sun and my camera. The effect was extremely strong. I guess this came from the fresh seeds, they were not sticked together like last year and showed real bright colours. I shot about 20 pictures and afterwards I went alomost crazy when I saw these intense clours on my PC. The pictures (12345678) were taken with a Canon EOS 350D and a Tamron AF 70-300mm Makro lense near Langgoens in Germany.

Author: Rolf Kohl, Langgöns, Germany

Compound Eye of a Horsefly

July 11, 2008:

I was very astonished when I was working and suddenly a horsefly fell upon my workbench.
The animal was about 3.5 cms in length. It was a very hot day, and the “flying fellow” had obviously lost his way, landed up in the workshop and could not find the way out. Well, the animal was lying there without moving, and the sunlight caused nice diffraction colours in its big compound eyes.

Author: Michael Großmann, Kämpfelbach, Germany