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.
Animation about the different refraction angle beetween salty water and fresh water.
Author: Michael Großmann, Kämpfelbach, Germany
This phenomenon is well known from the transit of Venus in front of the disc of the sun. This effect appears when the objects are not exactly focused (see: The black drop effect is not an atmospheric phenomenon). On Oct. 13th, 2013 I photographed this effect under unexpected circumstances:
The sun had just set behind the skyline of the Palatinate Hills across the Rhine valley, when a very bright contrail due to forward scattering of sunlight raised from behind the Hills. One of the hills covered the contrail, and the brightness contrast showed the drop phenomenon very nicely: the slope of the hill appears almost vertical where it is intersected by the contrail. Due to the far distance, I used the 13x zoom of the Canon Powershot A510. As the optics of such a small camera is limited, it provided the defocusing needed to show the effect. The sequence show the raising of the contrail during a time lapse of 4 1/2 minutes just after sunset.
If you may ask now: where is the “black drop”?: The “black drop” is somewhat hidden: it is the interface area between the bright contrail and the dark silhouette of the hill, where the “drop effect” raises the skyline showing an almost vertical slope of the hill in front of the contrail. The “drop” is best seen on the second and third frames from the bottom.
Author: Christoph Gerber, Heidelberg
Another article to this topic: The black drop effect is not an atmospheric phenomenon
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
Only at very rare occasions, light refraction can be seen as impressive as in this example. The photo was taken by Hermann Scheer at the Meteorological Observatory on Mt. Hoher Sonnblick (3105m) in the Hohe Tauern mountains in Austria. A layer of ice and rime had formed on the glass sphere of the Campbell Stokes sunshine recorder. This layer split the sunlight up into its spectral colours. That is how impressive physics can be.
Last night the webcam of foto-webcam.eu registered on Mt. Hoher Sonnblick (3106m, Hohe Tauern, Austria) stunningly St. Elmo’s fire again. And as in the first case, the small purple flames were not caused by thunderstorms, but by a combination of heavy snowfall and wind.
The diagrams show the measured field strength in conjunction with the fallen precipitation which is completely fallen as snow.
A time-lapse recordings of different webcam shows the unusual length of the St. Elmo´s Fire.
Thanks to Hermann Scheer from the Meteorological Observatory Hoher Sonnblick, Austria for the interesting material.
On February 20 and 24, 2013, unusual clouds which looked like NLC (noctilucent clouds) were observed by the pilots Terry J. Parker above Birmingham, UK, Nikolay N. Nikolaev and Egor C. above Moscow, Russia (picture at top).
In the AKM forum (AKM = Arbeitskreis Meteore/ Meteor Workshop) there were discussions on what could have been the reason for this unusual phenomenon.
- Polar Stratospheric Clouds can be excluded as a reason because the stratosphere was too warm at the time the observations were made (1-2).
- MAARSY (Middle Atmosphere Alomar Radar System) in Andenes, Norway, recorded strong echoes in the mesosphere. Weak echoes have also been recorded at Kühlungsborn, Germany. Mesospheric winter echoes are common, but up to now there are no special observations recorded which were connected to these echoes.
- There was a full moon on February 25, so high cirrus clouds illuminated by the moon cannot be excluded as a reason.
- The most probable explanation for the phenomenon is, however, that the clouds had been caused by the meteor which hit near Cheljabinsk, Russia, on February 15. A recent study by Kathryn Hansen shows that this cloud of smoke travelled around earth in an altitude of about 40 kilometres. This fits with altitude measurements made in Wales, which showed that the unusual clouds had formed at altitudes between 35 and 38 kilometres.
Another article to this Topic: “Noctilucent clouds in october ?”
Every day one can see shadows pointing away from the sun, but in rare cases there are also shadows visible in sunward direction. These shadows are projected against the sky. Seeing those spooky phenomena requires a low sun elevation, a high object which seems to tower above the sun, and a transparent “screen” of fog between the observer and the object. In the morning of September 11, 2013, Ulf Köhler observed such a phenomenon on the Hoher Peißenberg (998m). The shadow of the dome of the Mariä Himmelfahrt Pilgrimage Church appeared in passing wafts of mist. When Ulf Köhler changed his position within the shadow of the steeple, the shadow of the dome also changed its appearance. (1-2).
Another article on this topic: “Düsseldorf Leaning Tower and other Shadow Plays”
In August 2013, Ujj Ákos from Bátonyterenye in Hungary noticed light phenomena in a mosquito net for several times. There were phenomena visible (1-2-3-4) which resembled halos, similar to those in a spider web which Christoph Gerber photographed, but also iridescent colours were visible (1-2). Unfortunately, it is difficult to see what exactly causes the brightenings, although one can assume that they are caused by forward scattering of light along the different threads. But a mosquito net has no radial structure. So the reason of the phenomena probably lies in the grating of the net causing colourful light diffractions.
Diffraction patterns in fabrics can differ significantly and depend from the material used and its mesh. So crosses and paths of light are formed like those in this picture, or different kinds of coronae which can be seen here.
When passing a cross-walk, a colourful bow is not what one expects to see there. So Jordan Stabile was very surprised when discovering the colourful bow on the tarmac in Somerville, Massachusetts, USA.
The answer to this problem is a rainbow, but with the difference that in this case the light is not reflected by drops of water, but by transparent spherical glass pellets. These have a diameter of about 0,25 millimetres and are used for sandblasting especially at cross-walks. As glass refracts light in a bigger angle than water does, the bow is smaller than a normal rainbow, with a diameter of only 20°.
A glass bead bow can easily be reproduced by placing a lamp over a sheet of black paper, on which glass beads (available for example in building supplies stores) have been spread before. Then a colourful bow (photo) appears on the paper. As the distance to our two eyes is very small in this case, the bow can also seem to float tridimensionally over the paper.
While on my 4-wheeler riding around in the wood in Lakewood Wisconsin I came upon a puddle with a green film in it in the middle of a dirt road and I drove up to check it out and I am glad I did! As I was dismounting from my 4-wheeler colors on the puddle caught my attention and I found the same thing Marko Riikonen found algal optics. Over the period of 10 minutes or more I observed corona similar to pollen corona around sun’s reflection and Quetelet rings which I have always wanted to see. I also saw glory with the similar brightening’s like pollen corona and a white fogbow like glow around the glory. More pictures here.
Author: Michael Ellestad, Wisconsin, USA