Atmospheric Phenomena

New adress

2011-05-15T18:47:00.001Z

The blog is moved. The new adress is

http://blog.meteoros.de

High order bows

2011-04-21T21:24:00.004Z

A rainbow is a product of millions of falling raindrops interacting with sunlight. A single reflection form the primary bow, a double reflection forms the secondary bow. However, under ideal conditions there can be many more orders of reflection. As shown above, five, six and even ten internal reflections can be observed. Moreover, it's theoretically possible to detect twenty internal reflections, but the problem is to produce a perfectly spherical water droplet. The drops I used for this experiment were formed artificially. The light source is a 5 mW green laser pointer. Note that the bright spot at left center is the laser illuminated water drop.

The third and fourth order reflections aren't shown here because they, along with the seventh and eighth order reflections, are positioned on the other side of the picture in the direction of the light source. The primary and secondary bows will be viewed in the direction you're facing opposite the sun The fifth, sixth, ninth, and tenth order reflections are also in this direction. However, the third and fourth (as well as the seventh and eighth) order reflections can't be seen because they're behind you.

Under exceptional atmospheric conditions it may be feasible to see the third and fourth order bows if you're facing the sun, but they're quite faint. A third order bow, for instance, is one quarter as bright as a primary bow. A fifth order rainbow is only about one tenth as intense as the primary bow.

If you need more information about the experiments with high order bows, you can read this pdf.

Nikon D40X, focal length 18mm, 100 ISO, 2,5 sec. at f/6,3

Author: Michael Großmann, Kämpfelbach, Germany

Rays across the sky

2010-11-23T20:28:00.006Z

The photo features an array of anticrepuscular-rays as observed in Kämpfelbach near Karsruhe, Germany on July 31, 2010. I will never forget this sight. Sunset was fast approaching, and I first noticed faint crepuscular-rays above the western horizon. Just after sundown, the rays could be seen stretching across the sky from west to east. On this photo montage, east is at left center and west at far right. This display lasted for about ten minutes. To add to the show, the rosy glow of Earth's rising shadow (belt of venus) and the shadow band itself were visible just above the eastern horizon (left center). These anticrepuscular and crepuscular rays were cast by clouds below the western horizon. Viewing perspective makes the rays seem to converge toward the horizon; though, they're actually parallel.

Photo details: Nikon D40x camera; 16 pictures in vertical-order; focus length 18 mm; F/3.5; 1/60 second exposure time; ISO 100.

lightning

2010-11-23T19:10:00.004Z

The photo showing a classic cloud-to-ground lightning strike and a cloud-to-cloud bolt as well was taken at Kämpfelbach near Karlsruhe (southwest of germany) on August 22, 2010. Temperatures reached the mid 80s F (25-28°C) here by late afternoon shortly before a weather front and accompanying thunderstorm blasted through. The lightning was quite intense with this storm. I estimated 10-15 flashes per minute. Cloud-to-ground electrical discharges are typically observed when the base of the cloud is negatively charged and the ground is positively charged. On the other hand, cloud-to-cloud (inter-cloud and intra-cloud) lightning occurs most often when the top of the cloud is positively charged and the base negatively charged.

Photo details: Nikon D40x camera; F/9; 1/6 second exposure time; 18mm focus length; 100 ISO.

Dew bow

2010-11-23T19:02:00.001Z

The photo above showing a sprightly dew bow was captured in a moist field crop at Kämpfelbach Germany on the night October 22, 2010. Since the photo was taken at night, the illuminating source is the almost full moon which is directly opposite of the dew bow at the anti-lunar point. The mechanics of a dew bow are similar to that of a rainbow. Moonlight is refracted and reflected within the dew drops. The city lights in the background are Karlsruhe.

Photo details: Canon EOS 450D camera; F/4; focal length 8 mm; ISO 100; exposure time 30 seconds; 3 photos stitched together.

Discontinuous rainbow

2010-07-10T17:18:00.006Z

This is an older observation (from last year). I made it at the Langmuir Laboratory for Atmospheric Research on a mountaintop in central New Mexico, USA at about 10,500 feet altitude above MSL.

The photos look to the east-northeast. The rainbow occurs in a storm that is receding and drifting to the east and has just passed Sawmill Canyon in the foreground. The mountain ridge on the photo is called Timber Ridge, and most of the heavier rainfall is on the other side of that. The much finer, mist-like droplets near the trailing end of the storm are still falling in the canyon and create a rainbow that has a smaller radius and is a little wider than an 'ordinary' bow that occurs in larger raindrops. The effect is very obvious but requires a fairly specific landscape setting to be seen.

The photos were taken on July 27, 2009 using a Nikon D700 camera. Times below are local time (MDT).

Photo 1: The effect is just beginning to occur. 18:37:50 pm, 36 mm focal length, ISO 800, 1/160 sec at f/6.3.

Photo 2: Effect strongest. 18:43:17 pm, 38 mm focal length, 800 ISO, 1/250 sec at f/8.

Photo 3: The rainbow in canyon is disappearing and still shows a discontinuity. Also note that the 'foot' of the rainbow beyond the canyon is not following the circle but appears to kink - i.e. the radius is getting larger at lower altitude - maybe due to drops coalescing and increasing in size as they fall? 18:45:11 pm, 48 mm focal length, 200 ISO, 1/125 sec at f/5.6.

All three photos have not been cropped, modified or enhanced in any way.

Bird Feather Iridescence

2010-05-19T17:04:00.004Z

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

Influences of the Mt. Eyjafjallajökull eruption on the atmosphere

2010-04-19T13:29:00.002Z

In the morning of April 11, Mt. Eyjafjallajökull, a volcano which is covered by a glacier, erupted in the southwest of Iceland. Its cloud of ashes rises up to altitudes of 10 – 12 kms and has been shifted towards Central Europe by a northerly airstream since Thursday (animation).

The ash particles are slowly sinking downwards in the air, obstructing aviation in many places. In the atmosphere they dim the light (photos C. Hinz 1-2-3) and make Bishop´s Ring visible (photo P. Krämer), which is caused by light refraction on the aerosoles.

In high levels of the atmosphere, the particles act as additional nuclei for condensation, on which humidity (which under normal circumstances is not sufficient for cloud formation) freezes and forms ice crystals generating so-called “Invisible Cirrus Clouds”. Size and/or density of the ice crystals is in most cases not high enough to make the clouds visible, but their existence can be proved by the formation of faint halos such as sun pillars (photo Ina Rendtel), sundogs (photo Reinhard Nitze), or the 22°-halo (photo Brigitte Rauch).

There are still doubts regarding the appearance of the colourful twilight effects known from the eruption of Mt. Sarychev. Measurements with a Lidar effected by the Hohenpeissenberg Meteorological Observatory have shown that most of the aerosoles are at altitudes between 3.000 and 7.000 meters. A heavy rainshower should be enough to wash them out of the atmosphere and make the air clean again. An elevated concentration of sulphuric acid, which after the eruption of Mt. Sarychev formed several layers at different altitudes and caused beautiful purple light and afterglow effects, has not been measured at all. Probably the SO2 ejected by Mt. Eyjafjallajökull is chemically combined to water at the moment when the ash cloud is formed. The explosions, however, are generated by the contact of lava with ice, and every time a part of the glacier falls into the lava, there is plenty of water provided for such a reaction.

Authors: Claudia Hinz, Peter Krämer and Wolfgang Hamburg

Double Rainbow and reflected Rainbow

2010-04-16T19:34:00.005Z

When I wanted to go to work in the morning of February 24, 2010, I noticed a colourful rainbow forming during a short local rainshower. At first the weather had been fine that morning, and ist was almost calm, but then some rain clouds came up from the southwest and started to cover the sky. The sun was shining brightly at that hour (about one hour after sunrise) and made the rainbow shine in especially bright colours. So I hurried to get my camera and started to make some photographs. While I was taking pictures, I was astonished to see a third bow forming, which intersected with the secondary bow. At the first moment I thought that there was something wrong with my eyes, but I could see it also when I looked at the pictures already taken on the camera display.

I was excited, although I could not make head or tail of it – I had never seen such a thing before. Later, as I searched the world wide web for an explanation, I learned that the phenomenon must have been caused by a reflection. But the reason for the phenomenon was still not clear, as there was nothing between me and the rainbow that could have reflected any light.
Only much later I could solve the mystery: The reflection was caused by the Hallwilersee (Lake Hallwil), which was at about 3 kms behind the position where I had taken the pictures that day. The lake cannot be seen from the place where I saw the rainbow, as there is a hill between the lake and that place. So I did not take this possibility into consideration at first. The position and elevation of the sun, my position towards the lake and the distance from the lake fitted perfectly that morning to form this rare phenomenon for a few moments.

Author: Matthias Frei, Dürrenäsch, Canton Aargau, Switzerland

Bishop's ring

2010-04-02T19:36:00.005Z

Last Sunday, March 28, I went up on the Magdalena Mountains (in central New Mexico) to pick up two instruments from the laboratory there, and saw what would qualify as Bishop's ring around the sun for most part of the day. The mountain ridge lies at an altitude of about 10,500 feet above sea level. The sky was very clear and dry, and there was light wind at the time.

One of the photos I took is shown to the right. It was taken with a Nikon D700 with a 24-70/2.8 AF-S lens set at 24mm focal length and f/13 aperture.

To the eye the ring had a pronounced blue aureole with brown outer ring. I think the altitude of the observation rules out low-altitude aerosols being responsible. The central blueish aureole was relatively small; it was only a couple degrees in diameter. I estimate the radius of the outer brown ring to have been about 10 to 15 degrees.

Although the atmosphere was stable and quiet at the time I saw the ring, the southwest of the USA including New Mexico has had very strong winds and dust storms over the past week. In general, the spring months see many strong windstorms in this area. I believe the ring was caused by fine dust in the upper atmosphere and not from volcanic activity somewhere.

"Bubble Bow"

2010-03-23T19:09:00.004Z

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

„Glorydescent Clouds“

2010-03-08T12:50:00.004Z

In the morning of March 1st, 2010, I made my second observation of „glorydescent clouds“. These are fragments of a glory which change very much in diameter due to the different size of the droplets towards the rim of a short-lasting foehn cloud.
This makes the sequence of the colours look asymmetrically.
The stratocumulus lenticularis cloud did not even last for 5 minutes and caused a bright and very changeable iridescence or “glorydescence” during this short period of time. When the colours reached their maximum, up to 4 systems of rings were visible, with the 4th one appearing in the cloud behind the glory.
The pictures were taken at 8.05 CET / 8.06 CET / 8.07 CET.

Hair Ice

2010-02-26T21:18:00.004Z

Hair ice (in German Haareis) is formed at dead wood by conditions of high humidity and temperatures near freezing point. Water in the pores expands below 4°C and freezes on the surface. In this way fine ice needles were created. (1-2-3)

I found it in the Black Forest (Schwarzwald) in southern Germany.

Author: Helga Schöps, Germany

Halo Meeting of the “Arbeitskreis Meteore e.V. / FG Atmosphärische Erscheinungen der VdS e.V.“ at the Sudelfeld (Upper Bavaria), January 08 – 10, 2010

2010-02-21T09:46:00.007Z

Winter halos in nearby ice crystals are quite a rare sighting in most parts of Germany. However, there are few special places where the chances for such displays are much higher, such as the Alps mountains. To benefit from this, 14 halo enthusiasts met at the Sudelfeld Youth hostel near Bayrischzell in the vicinity of the Wendelstein (1838 m) during the second weekend of January. Already on Thursday (January 07) a very impressive halo phenomenon at the sun could be observed by Reinhard Nitze. Unfortunately, throughout the meeting a complete cover of low-level clouds blocked the sun so that halo observations were restricted to artificial light sources during night time. The highest halo activity was noticed at late Friday evening, involving light pillars (or superlamps), upper and lower 22° tangent arcs (“champagne glasses”), parhelic circles (visible for only few seconds), and superparhelia (not photographed due to fleeting appearance). The phenomena showed remarkable dynamics, lasting for about 10 minutes and being followed by intervals of 30-60 minutes without halos. The influence of snow blowers was discussed as well, since there were some of them running the whole night, approximately 500 m apart from the observation place.

Photo: Claudia Hinz

During the second evening only weak light pillars were seen for short times, eventually being replaced by fog bows due to rising temperatures and the transition from ice crystal to water droplet fog. Great fun were the shadow plays using a floodlight in the back of the people what finally led to photos of the “Sudelfeld monster”.Apart from the actual observations, the participants joined a workshop program containing slideshows from Michael Großmann, Claudia Hinz, Reinhard Nitze, and Andreas Zeiske as well as talks dedicated to special topics such as halo image stacking by Georg Dittié, high dynamic range image processing by Claudia Hinz, high precision measurements of the moon’s opposition effect by Elmar Schmidt, microphotography of snow and ice crystals by Reinhard Nitze, and artificial dew bows as well as stereo photography by Alexander Haußmann. The following experimental demonstration of glass bead bows in divergent light was received with great interest and triggered a high amount of photographic activity. Furthermore, an excursion to the nearby Tatzlwurm waterfall (named after some kind of dragon) was organized at Saturday afternoon and revealed a great winter landscape containing a large number of worthwhile photo subjects.

Photo: Udo Hennig

More pictures are here.

Author: Alexander Haußmann, Hörlitz, Germany

Colours inside a cracked piece of ice

2010-02-01T15:24:00.006Z

After some very cold days in Heréd (Northern Hungary) Karoly Viczian went out to the garden to break the ice in a rainwater collecting barrel. On a small piece of ice he cut out from the barrel he could see some very vivid colours - it reminds me to the diffraction colours of an opal gemstone. So maybe the coloures were produced by some microscopic bubbles inside the ice just the same way as they form in the gemstone that has small spherical structure . But Károly said he had noticed the colours after breaking up the ice, so it seems that the small cracks inside might have produced them with the help of birefringence.
As Károly told me the ice was the outcome of multiple freezing and melting periods, so it might also have separate layers inside. He has more pictures of the same piece of ice. The water was simple rainwater, only some fallen walnut leaves were at the bottom of the barrel, nothing was put in it willingly.
What is the correct explanation of this phenomena?

Iridescent Fireworks Smoke

2010-01-03T17:49:00.003Z

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.

Northwestern Germany Diamond Dust Sun Pillar

2010-01-03T17:45:00.002Z

Diamond dust halos are normally observed in northern regions of Europe, or in the mountains where temperatures in winter often drop sufficiently for the formation of ice crystals near the ground.

On December 19, 2009, there were several reports of diamond dust from the lower parts of northwestern and western Germany, which formed widespread sun pillars.
With temperatures of about -14°C, I also witnessed an upper and lower sun pillar in Bochum, Germany.
The lower sun pillar was visible in front of trees and even the snow-covered ground, as the picture taken at about 9 hours CET shows with the sun hidden behind a sign-board.
I could also see the ice crystals glittering in the air, making the pillar appear three-dimensional, as if a ray of light extended from the sun right up to my eyes.
The upper part of the sun pillar was visible for about half an hour, while the lower part and the glittering of the ice crystals stayed for about 3 hours until noon.

Author: Peter Krämer, Bochum

Crepuscular rays in desert dust

2009-11-23T09:54:00.007Z

After the twilights had been getting normal through the past three weeks, where hardly any volcanic aerosoles from Sarychev volcano had been measured, I was very astonished when I saw an intense purple light with crepuscular rays about half an hour before sunrise (sun elevation at -6°) in the morning of November 17. The crepuscular rays crossed the whole sky near the horizon, converging at the antisolar point (1 - 2 - 3).

Of course I immediately asked my colleagues from the Hohenpeissenberg observatory about the phenomenon. And I got a very surprising answer:
At that moment there were two different layers of dust from the Sahara desert above us, a lower one at an altitude of about 8.5 kms with dust from the western parts of the Sahara, and a higher one at about 11 kms, which contained dust from the eastern part of the Sahara. There were two different currents of air at higher levels which overlapped each other above the Alps.
It is new for me to learn that such twilights are also possible in desert dust, just as this dust up to now only caused a kind of certain dimness in the air. But at that moment there was no desert dust directly above us; I only looked into the layers of dust.

However, there was an extra bonus on the next morning. Unfortunately could only watch it from the valley:

Twinned rainbow

2009-11-19T09:18:00.003Z

Mark Worme observed this rainbow today at around 3.15 pm Atlantic Standard Time in central Barbados facing east. At first he only noticed the double rainbow, but then he realized the lower one was split.

During a heavy rainshower, a twinning of the upper part of a rainbow can sometimes be observed, which often lasts from a few seconds up to several minutes. As for a long time there were only few observations of this phenomenon available, only speculations could be made about its origin. Only in the past few years, this twinning could be registered more often by continuous observations, and due to some detailed descriptions, new theories could be advanced. As in all observations both bows are of equal brightness, light refraction on ice particles can be ruled out. Most probably is that raindrops of a non-spherical shape produce one of these bows or even both of them. Due to surface-tension, small rain droplets hardly change their shape when falling, but large drops can be flattened by the air resistance. The more flattened they become, the smaller is their refractive index. So the sunlight has to fall upon water drops of different size at the same time to make the twinning appear. As this twinning was up to now observed under big shower or thunder clouds which formed in hot air, it can be supposed that the small, not flattened raindrops evaporate at a short distance below the cloud basis. This would explain why the twinning can only be seen for a short time and exclusively in the upper part of the rainbow. It should be important to determine the radius of the rainbow when the twinning is observed, and to record the weather situation at the time the twinning appears as exactly as possible.

Shadows and lights of a flight

2009-11-15T04:50:00.006Z

Many people find flights boring - but not all! If you are lucky to be seated by a window you can always find something interesting in the air beside or below the airplane. David Lukacs from Hungary took this picture on 2nd November 2009 on a flight from Rome to Budapest, about 15 minutes after the departure. A thin layer of haze was between the plane and the sea so the sun shining on the right side above the plane could cast radial shadows on the left below. The beams of shadow and light join at the antisolar point.

A bit later when the plane travelled above a cloud layer David also noticed a nice glory below them:

Even the shadow of the airplane appeared in the middle:

Thunderstorm shadows

2009-09-17T10:29:00.003Z

In the evening of June 29, 2009, several thunderstorms formed unexpectedly over northwestern Germany, from the Ruhr area northward to southern Lower Saxony. They brought rainfalls up to 30 liters per square meter.

As the sun was almost setting, the shadows of the storm clouds reached a length of several hundred kilometers. The satellite picture taken at 19.15 UTC = 21.15 CEST shows the shadows extending even up to Thuringia and northern Bavaria.

Unfortunately, there are no reports on crepuscular rays from the area southeast of the thunderstorms.

Author: Peter Krämer, Bochum, Germany
Satellite image with kind permission of DWD (German Weather Office)

Interference Phenomena on Soap Bubble Surface

2009-09-06T18:28:00.005Z

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: 5 - 6 - 7

Author: Reinhard Nitze, Barsinghausen, Germany

Intense colours of a lightrefraction on fireweed seeds

2009-08-19T21:13:00.008Z

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 (1-2-3-4-5-6-7-8) were taken with a Canon EOS 350D and a Tamron AF 70-300mm Makro lense near Langgoens in Germany.

Author: Rolf Kohl, Langgöns, Germany

Reflected light dewbow on water surface

2009-08-11T15:40:00.003Z

I and my wife Eliisa Piikki got a hint about a light phenomenon on a lake nearby. Eliisa took some photos and there was a dewbow and a reflected light dewbow in those photos. They were formed on the waterdroplets that were settled down on the Chrysomyxa ledi needle rust (Small-spored spruce-Labrador-tea rust).

That rust can't be seen in Finland every year, but this year it is very common especially in the Eastern and in the Northern Finland. Because of the rust the young needles of some spruces are brown.

Author: Jari Piiki, Finland

Reflection rainbow (Lahti, Finland)

2009-08-07T16:42:00.004Z

On the evening 5th of August 2009, there was a reflection bow observed at city of Lahti. Marja Wallin saw and photographed a small fragment of reflection primary bow.
For the moment, the precise location of sun ray reflection is not yet analysed... To see her other rainbow photos for same evening, look at here.

Update (11th Aug 2009):
There is another gallery existing of the reflection rainbow, in same date and location, taken by Sami Luoma-Pukkila.

image (c) Marja Wallin

Volcanic Twilights

2009-07-21T18:52:00.007Z

On June 12, 2009, one of the most active volcanoes of the Kuril islands near Kamtschatka, which is situated near the northwestern end of the island of Matua, Sarychev Peak, erupted.

A NASA picture taken from the ISS gives an impressive sight of the eruption. Ashes have been ejected up to 20 kms into the atmosphere. Only a few hours after the eruption, the sulfur dioxide cloud of the volcano covered an area of 2.407 kms in width and 926 kms in length above the island. During the following weeks, the aerosoles spread over the whole northern hemisphere.

Since the end of June, also in Central Europe unusual twilights are observed. The up-to-date Lidar measurement from the Hohenpeissenberg observatory in Bavaria shows three aerosol layers in altitudes of 15, 18 and 22 kms in comparison to the eruption of Mt. Pinatubo. It is very interesting that the layers in 15 and 18 kms have come here with westerly winds passing over Alaska, Canada and the Atlantic Ocean, while the layer in 22 kms has been transported to us by stratospheric easterly winds passing over Asia (Russia/China). So the volcanic aerosoles have travelled around half of the planet in two different directions (the lower layers eastward and the upper one westward), meeting again here over Europe. I think this is worth to be mentioned.

On July 4, Peter Krämer observed the caracteristic crepuscular rays (picture above). On July 13, Reinhard Nitze photographed the most spectacular volcanic twilight in Barsinghausen near Hanover (Fig. 3). In his picture, the high aerosol clouds can easily be recognized. These clouds still receive sunlight while normal cirrus clouds are already within the shadow of the earth.

During the past few days, there were also noctilucent clouds visible, which passed over to the reddish aerosol clouds in lower layers. There should be unusual twilights visible also during the following weeks.

COMPOUND EYE OF A HORSEFLY

2009-07-04T15:05:00.002Z

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

MONASTIR RED RAINBOW

2009-07-04T14:53:00.002Z

On May 13, 2008, I was flying to Tunisia. Just before the plane landed in Monastir, I looked out of the window and saw a faint onset of a red rainbow. About one minute later, the rain became heavier, and the bow became more intensive, even below the horizon. Unfortunately, the plane landed about two minutes later, and I could not see if the red rainbow was visible from the ground.

Author: Michael Großmann, Kämpfelbach, Germany

BACKLIGHTED WATER VAPOUR

2009-07-04T14:50:00.007Z

March 10, 2009:

There is not always fine weather outside for making pretty pictures. So I tried to take some photographs of backlighted hot water vapour. Surprisingly, some pretty irisation colours appeared, which kept constantly changing in the rising “fountains”. Even after a short time, as the water cools down, the colours become less intensive as they are when the water is very hot.

Author: Michael Großmann, Kämpfelbach, Germany

Bochum Twinned Rainbow

2009-06-13T06:33:00.003Z

On June 9, 2009, another twinned rainbow appeared in the skies over Bochum, Germany. The phenomenon only lasted less than a minute, and I could watch the “twin ettect” move from left to right through the rainbow.

This picture has been processed to make the effect more obvious, but here is another picture showing how it really looked (1).

Just after the “twin effect” had disappeared, the rainbow reached a stunning brightness making supernumeraries visible as well as Alexander´s Band (2).

Text: Peter Krämer, Bochum, Germany

Pollen corona in Deventer, The Netherlands

2009-04-21T14:05:00.005Z

On April 1st 2009, Peter Paul Hattinga Verschure observed beautiful pollen coronae from his garden in Deventer, The Netherlands. Every time the wind blew through the pine trees, a cloud of pollen was blown away from them. When these clouds of pollen passed exactly in front of the sun, a beautiful pollen corona appeared. So, in one second it was bright and had three rings, in the next moment it disappeared again.

Tertiary Glass-Sphere Bow

2009-02-24T20:09:00.003Z

I have discovered a spectral reflection phenomenon inside a transparent plexiglass-sphere. The phenomenon, of which I am almost sure it is NOT the equivalent of the Primary or Secondary Rainbow, is in fact the equivalent of the Tertiary Rainbow, visible as a bright illuminating spectral colored ring all along the limb of the sphere. To see this ring, one should look "from behind" the sphere, toward the sun, with the sun "in front" of it (appearing exactly "in the centre" of the sphere).

The photo show the sphere with appearance of the red component of the spectrum. The distance of the observing eye (or camera's lens) to the sphere is VERY important, because the focal point of the ring is not a point, it's a spectral colored line (red at the far end, blue at the near end).

As far as I know, no one has ever observed or photographed the ring-like appearance of, what I call, the Tertiary Glass-sphere Bow (which has a focal point or "line", behind the globe!).

Author: Danny Caes, Ghent-Belgium

Fascinating moonrise during an atmospheric inversion

2009-02-05T20:28:00.030Z

After a bleak low stratus day, I decided to escape from the fog in the evening of the 13th of January 2009. I drove to the nearby Witthoh (Hegaualb, western Lake Constance, Southern Germany). There I wanted to record the rise of the moon – at least I hoped for a clinched moonrise, because of a prevailing atmospheric inversion.

Along the 860-metre-high Witthoh there was still a temperature of -10 degree centigrade. Two kilometers further away and 100 m higher the temperature was just 0 degree centigrade. Consequently, a very remarkable temperature layer existed in this region.
On the pre-calculated time, the moon’s upper margin pushed over the horizon.
What happened afterwards exceeded my boldest dreams. A “bubbling” of the rising moon followed as I had never seen it before.

Three times, approximately half of the rising moon completely detached from the lower half with red lightning.

The moon “boiled” on the upper half and it let vanish red and green rays upwards.

Only after circa 15 minutes, the moon calmed down completely.

Here is one more link of the moonrise as animated GIF file:

Kitchen optics

2009-01-30T18:54:00.022Z

An everyday kitchen can provide ample opportunities for observing optical phenomena, and as Mónika Landy-Gyebnár and Ágnes Kiricsi are not only good housewives but keen observers of such beauties, they always keep their eyes open for a chance of photographing something interesting while doing their household duties.

When you decide to drink your coffee in the early morning sunlight that just reaches your kitchen window, you might be lucky to get its steam of equal droplet size, and opening your eyes with the first sip of coffee you notice the colours of the drifting steam. You must have another sip to be sure that you really see the scattered sunlight and the display of iridescent colours.

If you use a spoon to stir your coffee with, don't run to the dishwasher immediately, but be a bit negligent, and wait till the coffee dries on it.

You may discover spectral colours again: patterns of thin film interference. Could it be the coffee's volatile oils or bacteria signalling problems of mouth hygiene?

Bisquits are always good to crunch with the morning coffee. Most of them are packed in a small cellophane bag that we can easily drop aside at the table by the window. And here comes the sun again - as its rays fall on the empty sachet, birefringence produces the well-known spectral colours again.

Not only human beings need a refreshment in the morning - our plants are also thirsty. And not only cellophane sachets are prone to showing birefringence, but transparent plastic flowerpots, too.

We have to pack a sandwich for the workday, maybe a good slice of ham - oops, the ham is also showing the spectral colours! The tiny (a muscle cell is about 10-80 microns in diameter), regularly arranged cells of the meat behave like the water droplets of clouds.

When the office hours are over, we still have some activities at home: for example making dinner for the family. Let's treat them with some meat balls, fried delicious in hot rainbow-coloured oil. Yes, rainbow coloured, as the afternoon sun still shines in, and the transparent oil bottle is placed in front of the window. You don't necessarily need a usm filter (or a usm sieve :)) to see the caustic patterns.

But be careful! Never cover hot food with a foil, otherwise they might produce colours again. First spectral ones on the foil, which we are happy about, but later a sickly shade of green on the meat itself. In this second stage, don't hesitate to throw the food into the dustbin.

Towards the end of the day, the work of the housewife has not ended yet. She's still on duty in the kitchen, looking at the pile of dirty dishes that has been produced.While the hot water gathers in the sink, it also steams a bit. There's no evening without a good streetlamp corona - you only have to look outside for a moment! The hot vapour has precipitated on the cold glass of your kitchen window, so the long day's last phenomenon wishes you good night with a colourful display.

Let's hope that reading so much about these household duties won't cause you nightmares of mugs carelessly washed up, and that one evening a brave man sits in front of the computer, and writes an article about the optical phenomena observed during his weekend-long tinkering in the workshop.

Shadows on ice crystals

2009-01-25T17:24:00.019Z

During the cold spell in the middle of January, some of us in Hungary started "experimenting" with snow crystals. As surface halos had been observed for several consecutive days (see the images of the odd radius surface halos by Ákos Ujj: 1 - 2 ), our basic idea was to find out whether we would see the trace of the 22 degree halo if we simply threw up the snow crystals covering the ground. Interestingly, the answer was yes. It was really exciting to observe that 22° from the sun, the crystals were glittering in spectral colours, and they faintly drew the form of the halo. Unfortunately, I was not so lucky with photographing the effect. All I could capture was the streetlamp casting its shadow on the crystals thrown and kicked in the air by Alexandra Farkas.

In the evening, however, Károly Vicián was much more successful. He had similar methods, but with longer exposure time, he did not only manage to photograph the shadow of the broom that was used to cover the spotlight, but the halo thus forming, too.

Perigee Moon

2009-01-17T18:07:00.013Z

This photo was taken by Claudia Hinz at the evening of Jan. 11th, 19.35 CET from Mt. Wendelstein (1838m), Southern Germany. The full Moon in this night was extra bright. Dr. Elmar Schmidt of the SRH University of Applied Sciences in Heidelberg, Germany, used an absolutely-calibrated photometer to precisely measure the moonlight and found it more than 50% brighter than that of a typical full Moon.

1. The Moon was at perigee, the side of the Moon's elliptical orbit closest to Earth.

2. The Earth-Moon system was near perihelion, the side of Earth's elliptical orbit closest to the sun. Extra sunlight increased the reflected luminosity of the Moon.

3. The Sun-Earth-Moon trio were almost perfectly aligned. This triggered a strong opposition effect an intense brightening of the lunar surface caused by the temporary elimination of normal shadows.

4. The weather conditions were optimal for photometry due to the clean and dry arctic air (its relative humidity being less than 10% at the moment of the photo). This resulted in only clear air scattering of moonlight with no extraneous glare as evident in the completely blue night sky. The brightness of the mountain landscape was additionally increased because of the reflection from the snow.

Elmar Schmidt details the relative contributions of each factor in his full report.

Text: Elmar Schmidt & Claudia Hinz

Effects in cloud bows caused by perspective

2009-01-17T12:02:00.003Z

In the morning of December 12, 2008, I coud observe a cloud bow on a stratocumulus layer, which was kind of perspectively cracked. Due to the ruggedness of the cloud surface it seemed as if there was a deep horizontal notch on the left side of the cloud bow.

But also this moonlight cloud bow, taken on September 9, 2008, seems to have vertical indentations and also an elliptical shape caused by the horizontal projection upon an uneven surface.

Sunset sequence

2008-10-24T12:35:00.001Z

This sequence of images of the setting sun was taken on September 14th, 2008, from Beverly Beach, Oregon, on an evening when sea mist partly obscured the sun. A vague green colour appeared on the upper edge of only one or two of these images.

Author: Alan Clark, Calgary, Canada

Volcanic Twilights over Europe

2008-09-08T16:13:00.003Z

On August 7, the Kasatochi Volcano, situated on the Aleutian Islands near Alaska, erupted. Clouds of ashes and sulfur dioxide were ejected up to 15 km into the stratosphere.

During the following 3 weeks, the volcanic clouds spread over the whole northern hemisphere, causing widespread intense twilight colours and often also crepuscular rays. These were first reported from Northern America during mid August, but at the end of the month, these "volcanic twilights" were also observed in Europe.

In the evening of August 29, several observers reported a strange and intense yellow light around sunset, followed by a purple light. Some of them were reminded of the unusual twilights between February 17 and 20, which were caused by PSC.

On August 30, skies were clear over Germany, and so many observers could see a kind of silvery cloud stripes a few minutes before sunset. These stripes were orientated north-south and at first glance looked like cirrus or cirrostratus clouds. But during the day these clouds had not been visible at all, and when looking at them carefully, one could see that they were higher than normal high clouds. The contrails of some airplanes were obviously below these clouds, and as the contrails turned reddish in the light of the setting sun, the clouds still remained bright. So they must have been floating higher up in the air, somewhere in the
Stratosphere.

After sunset, the clouds got a more brownish-yellow hue, but turned pink only about 20 minutes after sunset. Some observers also reported intense crepuscular rays. The purple light faded about half an hour after sunset.

In the morning of August 31, the colours and cloud stripes could also been observed. In the evening, a cold front with thunderstorms approached the western parts of Germany. While even the tops of the cumulonimbus clouds were already dark, the stratospheric clouds still lay in plain sunlight. That evening, instead of the regular stripes of the day before, they looked more like irregular waves.

During the first days of September, the strange twilight colours could still be observed over southern Germany, while for the rest of the country morning and evening skies looked quite normal again.

But as there are still volcanic ashes in the stratosphere, the colours may return. So keep watching the skies before sunrise and after sunset.

Author: Peter Krämer, Bochum, Germany

Glass Bead Rainbow on Kitchen Table

2008-08-22T08:18:00.004Z

The observation of a rainbow in glass beads on, respectively next to, a fresh route-indicator in a street I made by chance made me think about studying the effect also in the light of a street lamp. But unfortunately the glass beads had been scattered too much by the traffic within a few days. However, also by chance, I learned that glass beads are also used for facing the surfaces of, for example, metal objects, and so I asked our precision tool maker to bring me some...and then I started the experiment.

As a source of light I used a small bulb like those you find in a bicycle lamp, but without a reflector, because the light source should be as similar to a single point as possible. I scattered the glass beads on a black eloxated aluminum sheet (ca. 30 x 40 cm), and the result was overwhelming. Exactly as in the experiment made by Christian Fenn, the bow can be studied under different geometrical conditions when using a laser and a rotating mirror. The easiest way is to realize the reversed geometry just as otherwise the shadow of the head would be rather large as distances are small. Just put the metal sheet on a table, hold the lamp above it and look at it using different positions of your head. I also took some photographs after having attached the lamp to a mounting. This also shields the direct light. The first supernumerary is also visible, and like in the rainbow caused by water, a polarisation of light can also be proved. (1 2 3)

Seen through a microscope, the glass beads look like this:

I estimated the average radius to be at about 50 micrometers with an average variation of about 15 micrometers. But there are different sizes available. Similar to water drops of that size, the colours are rather blurred (this is especially obvious when you look at a glass bow in sunlight). The spectrum of light coming from a bulb is also rather "red" which causes the strange colours of the pictures.

As I was very fascinated by that phenomenon, I also calculated some simulations using the Airy-theory for glass beads (I could reuse some parts of the original text about the twinned bow for this). And in order to show the phenomenon from the observer´s position, I could use the text on halos on snow covers (so after 10 years the circle is closed...). An imaginary depiction seen from above obviously shows the "intersection through the apple", but as far as I know, nobody tried to explain the different width of the colour bands up to now. Tis effect becomes very obvious when "opening the inner bow by merging with the outer one" (This is very difficult to describe; you must have seen it). However, the geometrical data of the simulation are not exactly the same as in my observation because I did not execute any measurements while photographing.

Left: Seen from above with the observer´s position in the centre of the picture
Right: Gnomonical projection from the observer´s position (“simulated photograph”)

Author: Alexander Haußmann, Hörlitz, Germany

Yellow Rainshower

2008-08-19T13:51:00.001Z

On August 13, I could witness another atmospheric phenomenon in Bochum, Germany.

In the evening, about half an hour before sunset, a rainshower approached from the west. Behind the shower, the sky cleared up very rapidly, so that the low evening sun could shine through the veil of rain. This caused very strange light conditions I never experienced before.

First there was a yellow squall line visible, followed by a bright yellow veil of precipitation. As it came nearer, another shelfcloud-like structure passed from south to east. This cloud was also strangely illuminated and showed orange and brownish colours.

The squall line in the western and northwestern part of the sky turned more and more orange, too, while the rain got an intense and bright yellow. The whole landscape was bathing in a strange and intense yellow light with orange-coloured clouds above and in the east.

When it began to rain, a rainbow appeared in the east, visible as a full semi-circle. The blue part of the bow had already gone, only red, yellow and a faint green were visible.

Then the sun sank beneath the horizon, and all colours faded away within a few minutes. So there was no really red rainbow that evening, but nevertheless it had been very impressive to me.

Author: Peter Krämer, Bochum, Germany

Twinned Rainbow

2008-08-19T13:38:00.007Z

On August 13, after a rainshower had passed over Bochum, Germany, a twinned rainbow appeared. The bow was rather faint, but the twinning in its upper part was clearly visible. The red and the yellow colour bands of the rainbow were twinned.

On photographs of the rainbow, the twinning effect is hardly visible, but after oversaturating one of the pictures, the twinning turned out well.

During the rainshower, large drops were falling. A second shower about half an hour later with normal-sized drops also produced a rainbow. Even though this bow was very bright, it was not twinned, but showed a secondary bow and supernumeraries.

This is another hint for the theory to be right that the effect of twinned rainbows is really produced by large raindrops getting flattened by the resistance of the air when falling.

Author: Peter Krämer, Bochum, Germany

Light refraction on Fireweed-seeds

2008-08-15T12:30:00.008Z

While testing my new Tamron AFR70/300 on several plants and flowers I passed a very steep slope overgrown with fireweeds.The sun was relatively low above the slope that I noticed a silky lustre beetween the seeds. As more I was moving the plants beewenn me and the sun, the effect merged into an incredible refraction of light on the silky like seeds. I shot a few pictures and those which where slighty off focus showed very bright colours. This effect seems to be similar with light refraction on spider-webs. In this case though colous where extremely bright.

More pictures: 1 2 3 4 5

Author: Rolf Kohl, Germany

Summer twilight rays

2008-08-02T20:56:00.005Z

Bright twilight rays on 16 July, 2008 in Green Bay, Wisconsin. They stretched nearly all the way across the peaceful evening sky. This photo was taken 20 minutes after sunset. I enjoyed the view from our front deck for about 10 more minutes.

African dust over Europe

2008-06-09T01:58:00.006Z

In the last days of May there was an expansive dust layer above central Europe that caused a lot of interesting atmospheric phenomena. The story begun on 27th of May, when an ochre colored aureole surrounded the sun, and the sunset was pale yellow what repeated the next morning. There was a 7-8 degrees wide, dark greyish band by the horizon (image by Ágnes Kiricsi, in Vecsés, Hungary) this made the dawn to be late and the sunset to be too early. On the next days Bishop’s ring was observed through Central Europe – in the Czech Republic, in certain parts of Germany, and in Hungary. (This Bishop’s ring looks the same as it was produced by volcanic particles.)

In the Alps the dust strongly reduced the transparency of air (to about 3-4 kms).
The photo was taken by Bertram Radelow in Davos, Switzerland. The situaution was the same in the northern and eastern parts of the Alps.

The last two days of May passed away with the attenuation of the dust layer, dust fell out – both dry and wet way. At my hometown the dry version occured and a thin layer of fine yellowish powder subsided on the plants and the parking cars. In Germany there was a reddish-ochre coloured muddy rain falling that caught attention. The same thing happened at some places in Hungary too where rainshowers washed out the dust leaving muddy traces on everything.

In the meanwhile the dust „cloud” could even reach southern Scandinavia, where it also produced „colorless” sunset. The photo was taken by Andras Uhrin in Stavanger, Norway.

The origin of the dust is in the deserts of Africa. Late spring and early summer there are proper conditions in the Sahara and Sahel region for the fine dust to lift up high in the atmosphere where hot, dry winds transport it towards Central Europe, causing the same phenomena almost each year. There were „blood rains” in Europe caused by this Saharan dust over the centuries, like the ’Blutregen’ in 1901 in Germany, when the dust mass that fell out was 1-4 grams / square meter! The micron sized particles are mixed of fine sand and fine mica pellets.

Rainbows and supernumeraries

2008-05-06T20:33:00.003Z

During last weekend (Sunday 4th May -08) at city of Espoo, I observed seasons first rainbow. Local thunderstorm came along with rainshowers produring primary and secondary bows. I visually saw 3 primary supernumeraries.

In the heavily enhanced image (USM) of primary bow there is small hint of 4th supernumerary visible (1). Outside of seconday bow (2) there is larger arc (dark pink color), assuming it indicates supernumerary also... The droplet sizes may been quite even, due to easily visible interference bows.

Heiligenschein and dewbow in moon light

2008-05-01T13:20:00.005Z

Well, I wanted to observe moon halos that evening, but the sky was totally clear without any cirrus clouds.
I noticed that some blades of the plants on a field were rather wet. I walked some steps into the field and immediately noticed a clear brightening around the shadow of my head. I did a few steps to the left and to the right and could see a very faint dew bow. So I took some photographs at different exposure times and ISOs. The best photographs (1 2) I achieved using stop 4, an 18-mm-lens and at a time of exposure of 45 seconds at ISO 400.

Author: Michael Großmann, Kämpfelbach, Germany

Polarization Colours in Airplane Window

2008-04-03T09:58:00.007Z

Patrice Touhar took this photograph through the window of an airplane using a polarization filter and so made these polarization colours appear.

The colours are generated by the combination of three circumstances:

There is polarized light behind the window
The window is made of a double refracting matter
A polarization filter is used in front of the window

Under these circumstances, the light gets split up into two coherences of polarized components which travel through the window at different speeds. This causes a phase difference the amount of which depends from the wavelength. This means that the polarization gets transformed once into a linear polarization of a different direction than the origin for a certain colour, and into a circular polarization for another colour (Lissagiu interference of two waves). As the polarization is now dependent from the colour, the colours appear when a polarization filter is used, no matter if this filter is placed in front of the eye or in front of a camera.

These colours can be seen and photographed under the following circumstances:

There is polarized on one side of the window coming from the blue sky (Rayleigh scattering) and reflection from water and the scattering caused by clouds
The window is made of plastic. In this material there are mechanical tensions which cause a double refraction.
There is a polarization filter in front of the camera.

The last condition is not necessary if you look at the window from an acute angle. Then the light becomes already polarized by the refraction. In this case there is no filter necessary to see the colours. However, the colours you can see under this circumstance are fainter than the colours seen through the polarization filter because refraction polarizes only a part of the light.

You can also find another observation of this kind in this former thread.

Spectral Colours on Metal Surface

2008-04-03T09:05:00.003Z

During my work I noticed that a grinded metal surface divides the sunlight into its spectral colours (1 2 3). But this happans only when there are small scratches with a maximum depth of 0,003 to 0,005 millimeters. The scratches shown here are about 30 – 40 mm long, but unfortunately I cannot tell you what shape they are. The worked article was positioned horizontally on a workbench and the sun elevation was at about 50-55° (28.06.2007 at 11.30 hours CEST in Pforzheim). The visual angle onto the worked part was about 80°. The question I think about is: How can the white light be split up into its spectral colours that way, and, much more important: What shape of the hollow is necessary to reflect the spectral light this way?

Author: Michael Großmann, Kämpfelbach, Germany

Multiple rainbows

2008-03-11T10:21:00.004Z

Jan. 12, 2008
Riding home on the bus this afternoon, I noticed the rainbow off to the East. The sun was low in the west and was not far from setting, so the clouds were beginning to take on a golden hue. The rainbow looked like it was repeated numerous times and fading off in the distance. I got off at the next stop and pulled out my new pocket-sized digicam and snapped a couple of pics. I checked out Les Cowley's Atmopsheric optics page and it seems that the closest thing I could find were supernumerary bows, but these seemed to be more spaced out than the examples on his website. So is that what these are? I have included two pictures (1 2) and two contrast enhanced b&w versions of the pictures to better show the details (1 2).
Picture details: Canon SD1000, ISO 200, 1/160 sec, f4.9

Author: Darryl Luscombe, Vancouver, British Columbia, Canada

Aircraft Iridescence

2008-02-28T16:19:00.004Z

While taking wildlife pictures in a nature reserve close to the Vienna, Austria, airport, Franz Kerschbaum noticed this 747 jet aircraft in a landing approach with a huge condensation cloud behind its wings. As it moved closer to the runway, he was evidently at just the right position for this shocking but beautiful artificial iridescent cloud to come into view. Iridescence and coronas are diffraction phenomena. The pastel or metallic colors result from deflection of sunlight about minute water droplets.

Photo details: Canon EOS 30D camera, 100-400 mm/4.5-5.6L lens at 400 mm and f/8.0

Unusually bright twilights over Western Europe

2008-02-27T13:07:00.005Z

Between February 17 and February 20, 2008, large parts of Western Europe witnessed a series of unusually bright morning and evening twilights.
A few minutes after a quite normal sunset, the western skies began to burn in a strange yellow light which was bright enought to illuminate the landscape and giving a quite unreal touch to houses and trees.
Some minutes later, the yellow light in the west became surrounded by a brownish rim, turning into purple within some minutes. The yellow part of the sky slowly shrank towards the horizon, turning into orange and later into red and crimson. Some observers also reported of a dark, brownish-red light in the east which surrounded the whole horizon reaching up to 10° high.
The strange lights and colours in the sky were visible for up to about one hour after sunset. A similar “light-show” also appeared in the morning, starting with a crimson light over the eastern horizon and ending with the bright yellow light short before sunrise. The yellow illumination of the landscape could even be perceived through layers of low clouds (stratus) in some areas.
The phenomenon was reported from the British Isles, Scandinavia, The Netherlands and Germany, and there are even reports of unusual twilight observations from northern Spain.

These in some cases weird-looking twilights were probably caused by an outbreak of polar stratospheric clouds (PSC). These form at temperatures below -78°C in the stratosphere, at an altitude of about 20 – 25 km above the ground.
Soundings made at several stations showed that temperatures in the stratosphere really were unusually low over western Europe; up to -87°C (De Bilt) were measured, the lowest since measurements began in the 1980s. This makes the formation of PSC over a large area possible. Some photographs also show faint structures in the light, giving hints that they actually were caused by PSC.

Polar stratospheric clouds have never before been observed so far south. Normally, they can only be seen from Scandinavia, Canada and Alaska. Only in 1999 there was a confirmed observation of PSC from northern Germany.

Authors: Peter Krämer, Bochum & Claudia Hinz, Brannenburg

Unusual corona around the moon

2008-02-17T10:06:00.004Z

In the evening of February 14, 2008, an orographic cloud similar to this one formed above a sea of clouds under the influence of foehn wind above Mt.Wendelstein (1838m) in the Bavarian Alps. In this orographic cloud, an corona appeared around the moon which was more intensive and larger than any corona I had seen before. 4 systems of rings were clearly visible. The intensitiy leads me to the conclusion that all water droplets in the cloud were of the same size.

As I had a position very close to the cloud, the corona was extraordinarily large. A comparision to the constellation of Orion shows that it had a diameter of more than 20°. Below its lower part, the corona turned into a faint pink and green iridescence, indicating that the droplets were smaller towards the rim of the cloud. And it was also interesting that the thin cloud as well as the corona did not show greater changes in intensity and shape for about 4 hours. They only dissolved when the foehn wind broke down and the clouds of a masked upper level cold front came up.

Shadows casting shadows

2008-02-14T15:23:00.004Z

In the late afternoon of February 10, 2008, my friend and I went to a little pond on a field in Bochum, Germany, to take a few landscape photographs. It was a sunny day with a cloudless sky and no wind, so that the sun could be reflected very well from the smooth surface of the pond.
When we went along the pond, our shadows fell upon the water. As the sun was very low – it was about one hour before sunset – our shadows extended over the whole width of the pond, with the heads just beneath a bush positioned on the other side of the pond. Suddenly I noticed two fainter shadows just above the heads of our shadows, moving over the bush. When we stopped, these additional shadows appeared only as two faint stripes extending upwards across the bush from the heads of our shadows, as it can be seen in the wide-angle picture.

But when we moved, the phenomenon became quite obvious. So I did not only take a few photographs, but also made a short video with my digital camera. The video can be watched here.

What caused these additional shadows? First I thought that they were just the reflections of our shadows on the water, but when I later thought about my observation, I realized that it was a little bit more complicated:
The sun was shining on the water, and the sunlight was reflected from the smooth water surface. From the other side of the pond there could be seen a reflected picture of the sun in the water. This picture – or, better said – the reflected sunlight fell upon the bush, together of course with the direct sunlight. So the bush received direct light from the sun and also reflected light from the water surface.
When our shadows fell upon the water, the shadowed parts of the water could not reflect any more sunlight, so that the areas above the shadows received only the direct sunlight. So the parts of the bush which did not get the additional reflected light appeared less bright than the rest of it forming two slightly darker stripes extending upward from our shadows. So, what we saw were two secondary shadows, the shadows of our shadows. For a visual explanation of the phenomenon, I also drew a skech of the situation.

Never before I had thought that a shadow could also cast a shadow, and this observation was only possible because it was absolutely calm that afternoon. The slightest wind would have caused ripples on the water and thus blurred those secondary shadows.

Author: Peter Krämer, Bochum, Germany

Frost Optics

2008-02-11T04:25:00.001Z

2008/02/10 Taken in Green Bay, Wisconsin, USA at temperature of -10 F. I looked out to see the sunrise refracting through frost crystals on our back window. The entire pane sparkled with these delicate, miniature creations, but only a few of them were postitioned so that I could see the entire color spectrum at once.

Gree-blue Flash over the Canadian Rockies

2008-02-09T00:01:00.000Z

This sequence of sunset images was taken from the Canadian prairies, looking ovcr the Rocky Mountains from a distance of about 100 km, in mid-December, 2007. The remaining solar limb shows distinct blue colour following green tints, but the sequence ends with a faint red band, which is probably caused by faint clouds on the horizon.

Diamond-dust Sundog

2008-02-08T23:53:00.000Z

This very bright "localized" sundog was formed in ice fog among trees along the Bow River in Calgary on a very cold winter day recently. The remarkable feature of this sundog is that trees are profiled against it. The equivalent sundog on the opposite side of the Sun was almost as bright. These sundogs varied in brightness as ice-fog density varied. Individual ice crystals show up as transient bright points.

Icy window corona

2008-01-26T15:50:00.000Z

At the beginning of this winter season at a cold morning - dark outside - with a thin layer of hoarfrost on the inner side of the bus windows I've noticed that the light of the street lamps' light was not simply scattered on the windows, but having colorful corona around them. At that time I had no camera with me… All along the winter I was waiting for the same display each morning when some ice was on the bus windows, but for long weeks I haven't met with such spectacular phenomena again.This day was my day on 24th January. Very thin layer of frost was on the inner part of the windows, (with some frost ferns too by the corner of the window frame), mainly this layer was made of small uniform ice crystals made of frozen vapor droplets, we might call it an ice film, it was about 0,1 mm thin.All the lamps outside had a corona, no matter how far the lamp was.The street lamps with white light had the most beautiful color range, the orange colored light of sodium vapor lamps had a less distinct colors and they were a bit moved towards the reds. Not only the street lamps' corona was seen on the ice layer, but a much less spectacular corona around the reflection of the inner lamps of the bus too! At the part of the frost ferns pattern the corona became irregular in shape. When the lamp was near the window I could also see the bigger outer rings of the corona. Almost the same phenomena appears when simple water vapour is on the windows, but that one is really less poor in colors compared to the ice film corona.This was the first time when I could take photos of a corona produced by ice crystals. It's a pity, I could not take close-up photo of the ice layer itself (the bus was driving me to work so it was permanently moving).

Photos are collected here: The only afterwork was some noise reduction and size reduction. It was totally dark outside, so the pics were taken with ISO200 - ISO400; aperture F4 - F5,6; exp. 1/15 - 1/25 sec. auto white balance; without tripod or any kind of help to avoid moving.I wonder if the same phenomena would appear if the outer side of the windows would have a layer of hoarfrost on it. It's only weather's turn to show it up!

Author: Monika Landy-Gyebnar, Veszprem, Hungary

"Subsun" upon ice crystal

2008-01-10T18:14:00.000Z

While taking the photographs of the iridescent fissures in the ice, I noticed some beautiful ice crystal structures on one of the puddles. When I looked at them more closely, I saw intensive reflections of the sun in them. Animated by the hoar-frost halo I discovered before, I got the idea to photograph the reflection of the sun as a kind of “subsun”. To get the reflection completely into the picture, it was necessary to make a macro of the ice crystal. However, the crystal turned out ot be a lot more complex than I thought.

The reflection of the sun, however, was not a homogenuous surface, but appeared to be a slightly oval shaped, speckled white spot with a broad golden and also speckled rim. It is exactly this reddish-golden rim that gives me quite a headache, reminding me a lot of the reddish coloured fringes which sometimes can be seen at other haloes like parhelic circle or 120°-sundogs. The sequence of colours and the outward manifestation is that of a common aureole. However, in this picture it looks as if the colour came out of the inside of the ice crystals. Especially take a close look at the crystals marked with arrows.

About one week later at another frozen puddle, the reflection of the sun again had a reddish rim. But here the situation is quite different. This time it is a fragment of the frozen water surface. The wind has carried dust upon the ice which with the help of the sun had smolten innumerable tiny holes into the surface which originally had been smooth. Low temperatures then had made it freeze again. All in all, these processes have caused a rather permeable surface structure to develop, so the reflection of the sun is more like a diffraction. Especially in its upper part, there is an indication of iridescence. Who knows, on day somebody might succeed in taking photographs of “ice surface coronae”!

Last but not least: Of course you can also try to take a fragment of ice off a puddle and make some experiments with it. Maybe there will be confirmations of these sightings pointing also out to the possibility of a (additional) light refraction in the red rim.

Author: Reinhard Nitze, Barsinghausen, Germany

Silver Fir Diffraction

2007-12-31T09:17:00.000Z

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

2007-12-29T18:03:00.000Z

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

2007-12-29T17:49:00.000Z

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

2007-11-28T19:20:00.000Z

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

2007-11-26T17:50:00.000Z

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

2007-11-22T01:22:00.001Z

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

2007-11-20T15:31:00.000Z

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

2007-11-18T11:33:00.000Z

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

2007-10-01T15:47:00.000Z

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

2007-10-01T15:40:00.000Z

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

2007-09-22T04:19:00.001Z

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.

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

2007-09-20T22:22:00.000Z

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

2007-09-20T12:57:00.000Z

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

2007-09-19T23:43:00.000Z

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

2007-09-17T13:30:00.000Z

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

2007-09-17T13:09:00.000Z

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

2007-09-15T07:05:00.000Z

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

2007-09-12T16:51:00.000Z

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

2007-09-11T13:07:00.000Z

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

2007-09-10T13:47:00.001Z

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

2007-09-08T07:33:00.001Z

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

2007-09-05T17:23:00.000Z

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

2007-08-30T18:27:00.000Z

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?

2007-08-12T15:43:00.000Z

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

2007-04-22T15:16:00.000Z

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

2007-04-10T17:33:00.000Z

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

2007-04-08T14:48:00.000Z

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

2007-04-05T13:10:00.000Z

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

2007-03-08T17:51:00.000Z

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

2007-03-01T02:32:00.000Z

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

2007-02-15T11:44:00.000Z

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

2007-02-14T17:36:00.000Z

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

2007-02-13T18:26:00.000Z

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

2007-01-01T07:13:00.000Z

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.

Mother-of-pearl clouds in Finland

2006-12-25T13:15:00.000Z

A period of westerly tropospheric flows in Scandinavia is continuing to provide occasions of Mother-of-pearl (MoP) clouds to Finnish observers. Several MoP displays have been observed just before the Christmas at different locations, in particular in Central and Northern parts of Finland, but also at the Southern coast. The photograph taken by Mauri Laitinen in Kuopio, Eastern Finland, shows the beautifully coloured details of the afternoon display of 23rd December.

MoP clouds are seen a number of times each winter in Finland, but displays as bright as this one are fairly rare.
Usually the MoP clouds are related to stratospheric temperature colder than -80°C.

Alien hunt on the lake Königssee in Bavaria/Germany

2006-11-14T14:07:00.000Z

October 13th 2006 was a sunny and very warm autumn day, which we wanted to spend on a hike at the Königssee. However, we did not get very far because the scene over the very cold, deeply shielded mountain lake was entrancing. Ships flew over the water, islands floated in the air and aliens over the lake were hunted. It was really fascinating to pursue the fast changing mirages.

More Pictures: 1 2 3 4 5 6 7

Wendelstein Shadow and Rainbow

2006-11-10T19:55:00.000Z

After the passage of a front on August 12, 2006, the sky over Bavaria (Germany) began to clear up and turned into a sunny mood about 30 minutes before sunset. This image by Christoph Ries was taken looking toward the antisolar point as Mt. Wendelstein's (1,838 m or 6,030 ft) triangular shadow emerged over the Wildalpjoch Mountains (background). Both ends of this amazing rainbow were visible. By clicking on the image, you may be able to detect the faint left portion of the bow. Note that because the image was taken at altitude, the bow's nearly circular composition is observed. From flat terrain, we see rainbows as semi-circles, but when not confined by a horizon, it's easy to see that they're actually rain-circles. The image was stitched from three individual images using "autostitch" and "The Gimp."

Mother-of-pearl clouds over Colorado?

2006-10-31T06:15:00.000Z

Caleb Jones took this photo in Estes Park, Colorado (USA) on 28 October, around 3:10pm local time. The weather had been mostly clear on this day. These clouds were relatively far from the sun, and the vivid iridescent colors seem to be caused by very small droplets that polar stratospheric clouds have. But the edges of the wave cloud look more like regular mid-level waveclouds.

The 00 UTC 29 October sounding of Denver doesn't show unusually strong winds at high altitude, at 40 to 50 kts from the NW. In fact the entire troposphere seems rather dry on that particular sounding for lenticular clouds to occur.

I do not think this was caused by a missile launch either, considering the lenticular shape of the clouds.

I am wondering if these could be stratospheric clouds, or just some quite unusual appearance of lenticular mountain wave clouds. I received another report from someone else in Colorado who also took images, and am waiting for her approval to post them here as well.

2006-10-26T19:34:00.000Z

Brigitte Rauch and her husband spend every free minute on their motor-boat on the waters around their home island Helgoland, whichis only about one square km large and situated in the open North Sea. If possible, they do not miss any sunset and always have their camera ready to hand. This photograph of reflections on the water surface was taken on July 17, 2006, just after sunset. The colour of the sky and the clouds are reflected from the water surface, which was relatively smooth that evening. The patterns are caused by small waves. This richly coloured interplay of sky, clouds and waves can be seen only on a few days of the year.

More pictures: 1 2 3 4

Tunnel Glory in Italy

2006-10-17T19:38:00.000Z

Gerald Berthold spent the beginning of October in the South Tyrol, Italy. On 5th October 2006 he climbed the 2778m high Piccolo Lagazuio. The descent leads partly through tunnels dating to the First World War. Where they breakthrough the mountainside they give fantastic views of the Dolomites. On one of these galleries the sun shone along the tunnel through fog which developed because the humidity and lower temperature inside. In this formed a spectre of the Brocken with a spectacular multiple ringed glory (the camera is pointing away from the sunlight direction). The glory seemed almost graspable and was sensationally bright.

Small coronas from bacterial film on water surface

2006-10-15T12:27:00.000Z

Most of the cultivation pools in my room are now showing much smaller coronas than earlier. In each pool the corona is of constant size over the whole bacterial film surface, but from pool to pool their size vary.

Even though these coronas are smaller than before, they still are large as compared to pollen coronas. Unfortunately I have no photos for comparison.

In the composite image are two coronas photographed with same lens (not to scale with upper single image, which has been taken with zoom lens). The microphotograph of the bacterial film is from the smaller corona on the left.

The light source was a 50 W halogen spotlight that I made even more concentrated by placing the lamp in a cardboard box, into which a small hole was made for light to come through. When taking photos, the room was otherwise darkened.