Blog Archives

Full circle rainbow

Partly because of my embarrassment to capture any pictures of rainbow this year, I dug up my old idea about how to create a circular rainbow and went to a local shop.

After few hours with some assistance, a bent-looking sprinklers frame was completed (1). The first test on 2 June 2011 was somewhat unsuccessful because the sun was too high and I could not find a right angle to see the whole rainbow circle.

For a few days, rain storm after rain storm poured down over Bangkok, with no sunlight in the morning. On 5 June 2011, a heavy rain hit Bangkok again before sunrise, but the sun appeared around 7:30 AM. Many rainbow shots were taken (2) and the photos were stitched together by “AutoStitch” on a PC.

Place : Bangkok, Thailand
Time : Sunday 6 June 2011, approx. 7:44 AM
Rainbow Equipments : A row of sprinklers placed approximately 4 meters above the street
Digital Camera : Ricoh GX200 + 19 mm. wide angle lens
Exposure : 1/200 sec , f/4.1 , ISO 64, Daylight setting
Photo Processing : 4 pictures, stitched together by ‘AutoStitch’ on a PC, no image enhancement

Author: Pitan Singhasaneh, Bangkok, Thailand

Natural tertiary rainbow 3rd order

On May 15, 2011, a rain area moved from north to south. When it started to rain at my position, I immediately rushed to my observing site which is reachable within 2 minutes for me.

Once there, I saw beautiful specimen of the primary and secondary rainbow. During my observation,  the rain intensified, and now I knew hat I had to look for!

On the left side of the sun there was a relatively dark cloud bank providing ideal conditions for a possible sighting of the 3rd order rainbow.

In fact, I had the idea of seeing a very faint arc at the expected position of about 40° away from the sun. It is really exaggerated to say that I saw it, but there seemed to be something.

I went into the shadow of a tree in order not to be blinded by the sun.

Now I did not take any care to protect the camera from the rain, I just had a little box with me to put the camera into. The arc could not be seen for more than 30 seconds, but I´m sure there was something at that position.

As under those lighting conditions a correct exposure is hard to get, I took my photographs in RAW mode. All the “little helpers” of the camera had to be set off.

To my disappointment, I did not find anything at the expected position when examining my pictures on the PC screen. But when putting an unsharp mask over the pictures, I saw it immediately. A bow! You can see that the outer part of the bow is slightly red and the inner part is light green.

Here is an animation showing the original image and three different settings: Unsharp mask, intensified colours and inverted.

If you need more information about the measurements of this tertiary rainbow, take a look at this pdf-file written by Dr.Alexander Haußmann. Thank you very much for your calculation!

Author: Michael Großmann, Kämpfelbach, Germany

Intense colours of a light refraction on fireweed seeds

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

Author: Rolf Kohl, Langgöns, Germany

Light refraction on Fireweed-seeds

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

Rainbows and supernumeraries

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. Outside of seconday bow 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.

Posted by Timo Kuhmonen

Heiligenschein and dewbow in moon light

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

Multiple rainbows

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

Shock wave refraction and iridescence over airplane wing

The observation of Monika 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.

Author: Harald Edens

Colourful refraction by the surface waves

On June 13th Thorsten Falke from the German North Sea isle “Düne” (near of isle “Helgoland”) was walking along the seashore, when he saw criss-cross light structures on the seabed obviously caused by refraction by the surface waves. He had seen the phenomena often before but this time it seemed to be coloured. He decided to paddle out into the water to take pictures. It was difficult to see the colours visually because of the rapid movement of the little waves (only 2 cm “high”) but in many of the pictures the colours were evident. The appended picture was taken with a macro lens and shows a shell in 10 cm deep water with a colourful refraction band across it. Because of the macro lens the picture is nearly 2 times life size. Another refraction is located at the upper edge of the picture. If he remembers rightly, the light was coming from the left side and was parallel to the wave crests. The main interest of Thorsten is to observe whether the colourful refraction is seen only when the wave crests are parallel to the light direction or if it is also visible when the crests are at right angles to the sunlight.