Silver Fir Diffraction

The photo here was taken by Mónika Landy-Gyebnár. It shows light through the branches of a silver fir with thick, short grown needles. The camera was looking towards the sun and out of focus - just like in the spider web post of September. The curved structure is caused by diffraction. The image shows well-visible colours, and what makes the photo even more interesting is the horizontal lines across these coloured bands. Could it be some interference pattern created by the less spectacular slanting stripes on the side of the image? Or something else? More pictures

Shadow Rays above Pithead Rig

In the morning of December 21, 2007, a beam of shadow rays appeared above the pithead rig of the German Minery Museum in Bochum, Germany.

The picture was taken at about 10 a.m., one hour after sunrise. As the sun elevation was still very low, the shadow of the pithead rig was projected upwards and became visible as a beam of shadow rays in a thin layer of mist near the ground. A similar phenomenon can sometimes be seen above a pylon or tower, but there only one single dark ray appears. The shape of the pithead rig, however, made a beam of four shadow rays appear.

Author: Peter Krämer, Bochum, Germany

Colours on fissures in ice

In the late afternoon of December 15, 2007, temperatures began to stay below freezing 24 hours a day for the first time (!) in this year. Already the next morning, many of the small puddles on a lane near our town Barsinghausen were covered with ice. Children enjoyed breaking these crusts of ice with their feet. But at some of the puddles which had frozen down to the ground, they had no success and just caused some fissures in the ice. These fissures showed extremely intense colours.

The colours are probably caused by interference. Light enters the ice and is reflected to and fro between the edges of the fissures. So there are differences in the time the light needs to cover the distance between the ice and the eye of the observer. This causes light waves to amplify or extinguish each other. This is what we perceive as colours.

There is no direct sunlight necessary for this effect (1 2), but it can increase it enormeously (3 4).

Author: Reinhard Nitze, Barsinghausen, Germany

St. Elmo's fire in Switzerland

On Nov/14/2007 between 18:00 and 19:00 CET St. Elmo's fire appeared on a tower at the summit of Mt. Gäbris in Switzerland. The phenomenon was captured with a high sensitive video camera operated by Mark Vornhusen of Meteomedia, a private weather company.

There is a 25m metallic tower located on the summit of Mt. Gäbris (1241m). Three webcams are fixed on top of the tower, looking in different directions. One of these cameras shows a part of the tower, a metallic extension arm, in the outermost right corner of the image. St. Elmos's fire became visible at this extension arm.



The St. Elmo's fire developed during a snow thunderstorm. Only one lightning strike occurred during this storm. The strike is visible on the webcam images at 18:55 CET as a sudden flare of the image and was heard by the author, who lives 2km away from the summit. The lightning strike was not close to the tower, because the flare was not very bright. The cameras operate with a special software that is able to capture all bright objects on the night sky, even if the duration is only a fraction of a second (lightning, meteors).


The St. Elmo's fire was first visible on the webcam images at 18:05 CET and lasted about two minutes. The second and most intense appearance occurred between 18:40 and 18:50 CET, followed by the lightning strike at 18:55. During the 10 minute interval between 18:40 and 18:50 CET the weather station, which is also located on top of the tower, measured a wind gust of 75 m/s (270 km/h). This is obviously not a real wind speed. More likely it is an interference of the high voltage and the St. Elmo's fire to the anemometer. The ultrasonic anemometer uses sound speed to measure the wind speed ( http://thiesclima.de/usanemo.htm ).

To the authors knowledge it seems to be the first time ever St. Elmo's fire was imaged, at least a "classic" one that occurred on the ground and not during a flight on an airplane.

Animal Optics

In this blog we have already seen photos of spiderwebs scattering rays of light, and even a thistle seed showing spectral colours. Now I would like to contribute to this collection with another possible source for observing this optical phenomenon: cat's hair. The pictures attached show the dark Sámán (of Mónika Landy-Gyebnár) and the white Manci (my cat). When light comes from the appropriate angle, their fur can display the colours of the rainbow surprisingly clearly. Please, click the images to see it better. Full size photos of Sámán's and Manci's shining hair are also available.

The other photo is another "animal test". Given that birds' feathers have a very regular structure, I was interested whether they show corona-like diffraction if we place one in front of a light source. I found that the repetitive structure of barbs, barbules and tiny hooks interlocking on them create beautiful interference patterns. This picture - somewhat out of focus - shows an owl's feather (a secondary from its wing) with a lamp behind it. The pattern is curved because the feather itself has a bent surface. Further images: #1, #2, #3

Fog shadow of TV tower in San Francisco

Fog shadow of Sutro tower, San Francisco. These fascinating shadows look odd since humans are not used to seeing shadows in three dimensions. The thin fog was just dense enough to be illuminated by the light that passed through the gaps in a structure or in a tree. As a result, the path of an object shadow through the "fog" appears darkened. In a sense, these shadow lanes are similar to crepuscular rays, which are caused by cloud shadows, but here, they're caused by an object shadows.

A strange kind of glory

I have often seen glories which appeared to be elliptical (and not circular) or vertically disrupted. This was always caused by the projection onto an uneven cloud cover. But on November 18, 2007, I could observe a "vaulted" glory from Mt Wendelstein (1835m) in the Bavarian Alps. The strange glory appeared in an isolated stratocumulus cloud which adapted to the shape of a mountain. Its colours ended irregularly on its outer fringe like those of a glory around the sun which pass over to cloud iridescence. There is no circular shape recognizable in the colours outside the inner glory rings. The pictures are taken using a polarization filter and the contrast has been increased.

Another observation which might be related to mine, has been made on January 01, 2007 by Stefan Rubach on Mt Großer Arber.

Perspectively broken shadow

When there are swelling cloud parts on the surface of an unbroken cloud cover, it sometimes can happen that the shadow of a pole projected onto this cloud cover appears kind of broken. I could observe such a shadow broken perspectively on August 18, 2007, at 18.15 hours CET on the top of Mt. Wendelstein (1835m), when the shadow of the transmitting aerial of the Bavaria Broadcast fell upon such a cloud cover, surrounded by a glory which appeared three-dimensional.

Colourful bacteria film

On September 14, 2007, Reinhard Nitze saw intensely iridescent colours in some puddles on a lane near Barsinghausen/Egestorf (Lower Saxony, Germany). These were probably caused by bacteria of putrefaction coming from decomposing grains of wheat in the water, just as the colours showed up only in those puddles containing larger amounts of grains. The grains originated from the fields along the lane and had probably fallen from a trailer when the harvest was brought in.As some of the grains were already covered with green algae, they must have been lying in the water for some time already. Also remarkable was the rusty colour of those puddles which had already fallen dry.

more pictures

Glowing Spider

On Sep. 29. 2007 at a late afternoon cakewalk I observed this glowing spider above a steep sunside slope between low hazelnut trees. I couldn't get closer than abt. 3 meters to the object, so the size of the image became limited. The canon tele EF70/300 did i relatively good job on taken the image freehand . The spiderweb also showed nice colourful reflections of light from the sun.

Author: Rolf Kohl

Shock wave refraction and iridescence over airplane wing

Ágnes' post with the beautiful colored contrail pictures made me remember to post the following photos. On a flight in a 747-400 from Beijing to San Francisco on August 18th I was seated right over the wing on port side of the aircraft. Initially I was disappointed with this window seat but I did get to see some interesting things.

The first of these was a condensation cloud over the wing. The airplane was still ascending around 20,000 ft, when we flew through (super)saturated air. The faster airflow over the top surface of the wing and associated drop in pressure caused condensation. The cloud showed beautiful iridescent colors. The water droplets in the cloud were so small at this stage and all so uniform in size that they diffracted the light with constructive interference over large angles.

On the second photo this condensation cloud extends behind the wing. This is because it takes energy for a water droplet to form in supersaturated air, but once the droplet forms it quickly grows (or it quickly evaporates if the air is not supersaturated, as in the first photo). In other words, when the air is supersaturated, all that is needed is a trigger to initiate droplet formation, after which growth occurs because the air is supersaturated.

This droplet growth is responsible for the colored trail between the exhaust contrails that can sometimes be seen, as in the photos posted earlier. But most often, the air is either not supersaturated, or already condensed into a cloud. Then, no long trail forms (only the engine contrails perhaps), or it is not visible (within cloud). Therefore it is not common to see this effect, especially from ground.

At times a huge and bright corona formed around the sun. In this photo the airplane was banking right and the sun appeared low over the wing. My apologies for the low quality photo - it is very hard to photograph through an airplane window with the sun in view.

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The other interesting thing, which I had observed before, but only now could photograph well, is the vertical standing shock wave that sometimes can be seen dancing above the wing of a commercial jet. Here, because of the condensation cloud, this shock wave actually became visible. Usually it can only be seen due to the feeble refraction and miraging of structures on the wing (you won't notice this unless you look very carefully and at the right moment when the shock is positioned so that you are in its plane).

The normal shock occurs because air flowing over the wing has to flow faster than below it, and this flow can briefly reach the speed of sound even if the jet airplane is flying slower than the speed of sound. Because the Mach number is about 1, the shock wave is almost perfectly vertically oriented, normal to the airflow.

The shock plane in the photo can be seen as the vertical plane of enhanced condensation. I believe this is the rarefaction shock (as opposed to the compression shock) because condensation is enhanced behind the plane, indicating lower air pressure. Presumably the compression shock was somewhere ahead of this, invisible to me since I was not positioned in its plane.

The sharp density gradient at the shock wave causes a lateral mirage, but any miraging can only be seen if you are looking near grazing incidence along the shock plane (which is usually not perfectly planar but a little curved). The last two photos better show the miraging along the shock plane. Note the effect on the pylon of engine nr. 1.

homemade reflected-light rainbow

Though these photos are old but when it come to making rainbows with garden hose sprays this is an unusual one. I knew reflected light rainbow required a smooth body of water to form and at the time we still had an above ground swimming pool and its surface was glass smooth and I got the garden hose turned on and saw not only primary and secondary but in between those was a reflected light primary! I continued to experiment and I got some photos with the old Kodak DC215 which has been retired since I use my Nikon D-100. I don't know if anyone has ever tried a homemade reflected light rainbow with a garden hose and a smooth surfaced swimming pool but mine may not have been the first or the last.

Contrail Colours

These two photos were taken by "Controll" and Mónika Landy-Gyebnár (Noli) in Hungary. The pictures show wonderful colour stripes in the contrails. The most fascinating thing is that the stripes have the airplane as their centre instead of the Sun, and as the plane was flying, the colours did not change depending on the angle to or the distance from the Sun.

The explanation of this phenomenon may lie in the varying consistency of the exhaust. The water vapour condenses, freezes, and the ice crystals become larger and larger. During this process, the refractive characteristics of the particles constantly change, and if the circumstances are ideal and the trail is not too thick, we might see such beautiful colour patterns. For the explanation, we owe thanks to “Uncinus”.

There are more photos available in this topic. See Controll's collection of colourful contrails and another picture taken by Mónika Gyebnár-Landy.

Spider Web colours

Thie picture of light reflected from spider webs, looking on a direction towards the Sun, with 2-stop underexposure and the camera out of focus. Note the fact that, although the web strand is out of focus in the direction at right angles to the strand, the colour bands are sharp in a direction along the strand.

Resin Bow Effects

These primary and secondary refraction effects from droplets of resin onspruce tree cones produce very intense colours, at 20 degrees and 90degrees from the Sun direction. The photos were taken out of focus and twostops under normal exposure to avoid colour saturation. In the secondarybow, there is some evidence of "supernumary" colours beyond the violet endof the spectrum, as evidenced by pink colour of the reflections.

Author: Alan Clark

Reflected-light Rainbow

This image was taken during a violent storm that produced golf-ball-sizedhail as it passed over. The interesting thing about this reflected-lightbow is that there was no large body of water to produce the reflection. The source of this reflection was most probably a wet highway, theTrans-Canada Highway, west of Calgary. Since this part of the highway wason a hill, the reflected-light bow appears relatively high compared to theexpected position from a horizontal reflection surface.

Author: Alan Clark

Reflection of camera flash-light in a glass of white wine

A good friend of mine is celebrating his birthday early in September. Recently, we celebrated his 53rd birthday on a Saturday evening in an Indonesian restaurant in the centuries-old city of the town of Utrecht, in the central part of The Netherland. This (school)friend was one of the three guys who initiated a group of youngsters at the end of the sixties and the start of the seventies (of the 20th century), interested in astronomy, weather and ... optical phenomena. The initiative grew out to the nowadays Dutch "Vereniging voor Weerkunde en Klimatologie" and the "Halonet" optical observers group.
During the superb birthday dinner, one of the people of the restaurant made a picture with a digital camera-with-flash-light, while we were toasting for the health and wealth of the hero of the feast.
Absolutely by chance, it happened, the flash-light of the camera reflected in the glass of white wine I raised for the toast (the yellow "light" clearly visible in the picture).
It seems, some people are just born for optics ...

Mysterious colours in the thistle seed

Helga Schöps searches ardently for color dispersion effects in nature (like this close up of the banded diffraction pattern). Rainbows are not the only source. Helga photographed these recently at Hermsdorf, Thüringen, Germany. One is evidently a partial rainbow produced by dew drops on the fine hairy structure. The other colours in the thistle seed heads are more mysterious. Do you have an explanation?

posted by Claudia Hinz & Les Cowley

Reverse Lamp-Rainbow

On August 31st at 01:00 I took some long-time exposures of the Westerhever Lighthouse in Nordfriesland (Germany). It was raining a bit but this didn't matter because I wanted to display the rays of the lighthouse. Home again I reviewed the photos and was a bit surprised about a kind of arc, originating at a point in height of the lantern room and sloping downwards until it ends +/- horizontal (see pictures 1 2 3). I thought it could be a type of refraction phenomena but I couldn't explain to me what is was exactly. So I placed the pictures in the Meteoros-forum. Mark Vornhusen and Christian Fenn told me, that this arc is a type of rainbow called "reverse lamp-rainbow" and that these photos are probably the first displaying this phenomena. Both a 42 degree arc as well as a 51 degree arc are to be seen at the pictures.

The rainbows originates from the horizontal Lighthouse-born lightplain cutting the hull of the "Minnaert-cigar", an apple like shaped figure that describes all those points in which light coming from a source of light is reflectet in an angle of 42° respectively 51° to an Observer. In case of an usual source of light at every point of the Minneart-cigar a rainbow is being generated. But because of overlaying of these rainbows the colour-addition leads to a white light and no rainbow can be seen. However the thin light-layer of the lighthouse-beam only allows forming of rainbows at a small window of the minnaert-cigar and the rainbow becomes visible.

Author: Achim Christoph

Divergent light fogbow

Observed at Tuula (Estonia) on 10th September at 00:30. The fog condition was perfect at the time for the glory's rings merge into multiple supernumeraries. But the location was perfect as well which is surrounded by forest from east and west side generating the wind tunnel to blow the fog from the bog field in north or from the river in south. As long as I remember this location has been always very foggy and has been often flooded in spring-time. The light source I used was Johnlite-2940, which makes the car's headlights a joke.

I also observed a very bright and colourful glory and took some close-ups.


at 43mm.

http://www.mkruselphoto.com/content/bin/images/large/IMG_5446g.jpg at 24mm
http://www.mkruselphoto.com/content/bin/images/large/IMG_5445.jpg at 30mm

Thin film interference on the water surface

In the city of Lahti there is a landfill hill from which base in some places flows iron rich water. The bottom of these ditches is rusty brown and water has a strong iron smell. In some locations the water surface is completely covered with a film that displays spectacular colors in cloudy weather. This film is caused by iron oxidizing bacteria. The bacteria itself resides in the water, but it produces on the water surface substances from which it hangs down like a chain of sausages. Iron oxide is one of these products and it may be the cause of colors.

Announcement of an eventual International Optical Meeting next year in The Hague The Netherlands

Dear fellow sky watchers,

at the moment, Peter-Paul Hattinga Verschure and I are making preparing efforts for an eventual International Optical Meeting, next year in The Netherlands. Our first aims are:

- to find a proper location for the meeting, and

- bring in sky watchers, interested in the proposed meeting, as many as possible

In this stage, I have contact with the staff of the organization of the yearly Eurasian festival "Pasar Malam Besar" (P.M.B.), here in The Hague. The staff of the P.M.B. is interested in our project, and is inclined to give hospitality to an eventual International Optical Meeting 2008 in The Hague.

If you want to learn more about the preparing efforts concerning the proposed meeting, please click on this link.

Thank you very much for your attention!

Frank Nieuwenhuys
The Hague, The Netherlands

Strange Rainbow

Reinhard Nitze observed at Barsinghausen (Niedersachsen, Germany) on the morning of July 7, 2007 a strange rainbow produced by a passing shower. Owing to the low solar elevation it had a predominantly reddish colour. When he saw the photos he remarked on the strange step change in brightness, colour saturation, radius and width near the left-hand base of the bow (photo with unsharp mask). The change is marked on the photo by an arrow and is not an artefact because it is present on other images (1 2 3). The upper part of bow is considerably brighter and more strongly coloured although blues are weak and violet is completely absent. This is not easy to explain. A cloud might be shadowing the weaker part of the bow but that does not explain the width or radius change. Smaller drop sizes in the lower region might be responsible and could be obscuring rays from larger raindrops further away. Effects of reflected light bows can be ruled out because no water was nearby. Somewhat similar unusual rainbows were imaged by the Japanese observer Yuji Ayatsuka.

Purple sun?

These pictures were taken on a flight from Geneva to Warsaw on 18 July 2007. Shortly, after the sun disappeared behind a bank of clouds, I was surprised to notice that the LCD display of my Lumix TZ-1 camera was showing a purple sun. As purple is not a colour not normally associated with the sun, my first thought was that my camera had been damaged by taking pictures of the sunset. However, it soon became clear that the camera really could "see" the sun - despite the fact that the sun was completely invisible to my eyes! In fact, the sun remained visible to the camera for about 2 minutes after it disappeared according to my eyes.

Notice that the sun appears to have been squashed vertically (due to atmospheric refraction).

The explanation for this phenomenon is that the CCD sensors used in digital cameras have their peak sensitivity in the infra-red - typically at a wavelength of about 1000 nm, which is well beyond visible spectrum of 400 - 700 nm. You can test the infra-red performance of your own digital camera by pointing a TV remote control at the lens of the camera from a distance of about 15 cm (6 inches). Most remote controls transmit infra-red at wavelengths of 850 - 1000 nm. Your camera viewfinder will probably show a purple light when you press a button on the remote control. The purple colour suggests that the red and blue sensors in the camera are sensitive to infra-red - but not the green sensor. Hence, the purple sun .....

Algal optics

The season for algal optics has started, the first display was seen here in Finland already in the beginning of April. No photos was taken, but a gallery from my work on this stuff in last summer is here.

The algal films that display optical phenomena are clearly not as rare as have been thought. In the Baltic sea rocky islands about every 10th freshwater pool came with algal optics last summer. In Bulgaria, the species Chromophyton rosanoffii, which is responsible for the phenomena in the photo, has been described as common.

When it has not been raining for some days, go look for any freshwater ponds, puddles and pools. If the water surface is covered by a thin film, chances are that some sort of optical phenomena is visible in the sun light.

Flag corona

Light diffraction doesn't only originate from aerosols like little water droplets or pollen floating freely in the atmosphere, but also from so-called diffraction gratings. These consist of a large number of equally spaced holes or slits, from which the light rays interfere and form an interference pattern. In this example, which I photographed in the beginning of April, the thick woven fabric of the European flag serves as a diffraction grating and shows a beautiful corona.

Green and Blue Flash

On December 26th I climbed the 1000m high Plettenberg to observe and photograph the setting sun with 1m focal length to look for the green flash. The transparent air and an inversion layer were promising, however a few clouds with their top at approximately the same altitude were disturbing. The upper limb of the sun turned out to be quite turbulent showing green rims and flashes, but also some blueish apparitions.
Why a blue flash?
A green rim of the setting or rising sun occurs due to differential refraction in the atmosphere. If conditions are extremely clear, also the blue light has a chance to get through, and there might be even a blueish rim. With a temperature inversion layer in the atmosphere, upper segments of the solar image might get separated from the rest of the solar disc. In the final moments of these elusive segments they do appear green and sometimes even blue (green or blue flash). However, it is not clear to me why in my observations both happens. Most last moments are green, whereas the third frame shows a blue color and at the same time other turbulent segments with a green color. Should not every segment turn from green to blue, at least in the very last visible moment?
Maybe something more than just clear air plays a role for a blue flash visibility!?
It is the first time I see green and blue flashes simultaneously in one image. I strongly encourage other observers to record video data to show these effects in higher time resolution.

See large image with blue flash
Image sequence with description

Colours in the airplane window

While flying from Izmir to Ankara in Turkey on monday the 2nd of April 2007 at 10.15am Selen Ediger wanted to take an aerial shot of the mountains below with my canon ef 10-22mm lens and Hoya multi coated polarizing filter. With naked eye the colors were not visible but when she looked through the camera she saw that the land and the sky was covered with rainbow colors. The contrast and the saturation are adjusted a bit.

What's the origin of this colours?

Reflected rainbows near Spitsbergen

On 22nd August 2006 between 20.35-20.50 hrs, while cruising on the Isfjord near Spitsbergen, Nicola Boll watched these wonderful reflected rainbows. The lower bow is an ordinary primary bow. Intersecting it and curving upwards above it is a 'reflection bow'. The bow is formed by sunlight reflected off the smooth waters of the fjord. The upward going reflected rays are, in effect, from a 'virtual sun' the same distance below the horizon as the real sun was above it. Since rainbows are always centred opposite the light source, the centre of the reflected bow is up in the sky and the bow correspondingly high. In the picture enhanced by unsharp masking a reflection bow is also visible curving upwards above and to the right of the secondary rainbow.

Rainbow season started early with a twinned primary

While homeward bound from work a small rainshower started to pour in bright sunlight and I looked the the north and got a flat looking rainbow. I was ride-sharing when this happened and we pulled over and I got some photos and the bow looked unusual. Upon downloading the photos I applied unsharp mask and noticed the primary was twinned primary bow. This is the first rainbow for me this year. I would of expected to see one in the spring not February!

Extremely bright cloud iridiscence in Spain

On Saturday, February 10, 2007, Ramón Baylina shot these photographs of incredibly bright and colouful iridescent clouds at the Port of Tarragona (Spain). The pictures were taken at about 5 pm with a 200-mm-zoom lens."

More pictures are here

Mountain Mirage in Germany

In December 2006, some very prominent inversions formed in Germany. On two days mirages were observed along these inversion layers.

In the morning of December 15, 2006, Rüdiger Manig could see the miraged Fichtelgebirge from the weather station at Neuhaus am Rennweg in Thuringia, which was situated directly above a sea of clouds when he made his observation. The distance between the Fichtelgebirge and Neuhaus am Rennweg is about 70 km. The photograph shows Mt Schneeberg (1053 m) on the left and Mt Ochsenkopf (1023 m) on the right.

On December 23, 2006, Stephan Rubach saw the Alps main ridge in a distance of more than a hundred km from Mt Grosser Arber (1456 m) in the Bavarian Forest. Also he stood above a sea of clouds when making his observation, and the layers of air of differnent temperatures let the peaks of the Alps grow upwards in an abstractly distorted way.

Winter Mirage in southern Finland

The image was taken by Timo Kuhmonen at last weekend, on Saturday 10th February 2007. Place is near to Helsinki / Finland (Lauttasaari).

Timo was outside on that day hiking and taking some winter weekend photos. He had seen the mirage above frozen sea, distant island was "floating" on the air.

Temperature on that morning at his house in Espoo was -20°C. At the place where photo was taken, temperature was higher. Propably there has been enough of temperature differences in the air layers to produce this "winter mirage".

Fireworks corona

Wolfgang and I spend New Year's Eve 2 years ago on the top of the Wendelstein Mountain. 100m lower down was the "Wendelsteinhaus" tavern with a party in full swing. After midnight the party fireworks detonated at our level in front of our eyes. The flares illuminated some fog patches from the valley and produced greenish and brownish coronas. Some of the original flares could have been green but the effect could also be due to scattering from the firework smoke particles. We wish you all a wonderful New Year and hope that you see this and plenty more atmospheric optics phenomena in 2007.