Making sense of the elusive twinned rainbow (in the lab, and in reality) Part 2.

A few weeks ago, while I was waiting for a bus at 9.30 am, I suddenly saw two rainbows popping up in front of my eyes out of the blue. One of them was really close (yes, I know, there is not one rainbow closer than another, blah, blah, all at infinity...) while the other seemed to be miles away. There was no rain at all where I was, but a stone throw away (where the closer rainbow was struttingly showing its colours) there was a weak and lonely shower falling slowly from the sky. Miles away, though, the far rainbow was clearly born out of a serious armada of black clouds and heavy rain. As for the sun, it was really struggling to cast its light through the short-living gaps that infrequently appeared between a long array of fast moving clouds. No wonder the two rainbows seemed to have come out of nowhere.

The bus was late, and for about ten minutes I had the pleasure of seeing with my own eyes how strikingly the 'settled' issue of the rainbow phenomena was proving to be just another scientific myth. The sun was definitely not behind me, and it was creating two separate rainbows in two different places. The bands of colours in the closer rainbow were significantly broader than those shown by the far one. The sun was pretty much at the same level on the sky with the close rainbow. Ten minutes is a lot of time in the realm of a human brain, and by the time the bus was finally arriving my brain had already scanned for my inner eye a huge number of pictures with rainbows that were being pushed into a corner approved by the currently reigning establishment of physicists. I won't be talking now about those, though. Today the time and space are solely dedicated to the subject of twinned rainbows.

Obviously the screenshots above are outdated by about eight years now. That's because in the last months of 2011 a group of scientists succeeded to simulate on computer how twinned rainbows could be created in reality and a few short months later the entire community of physicists apparently agreed with them. Some say that it's been rather surprising to have taken so long to fully understand the rainbow phenomena, since the basic mechanism of their formation has been (according to the mainstream establishment of physicists) well understood for a very long time. Others, on the other hand, believe that the mainstream academia is still a long way off the track in that subject. And, of course, as you well know, I'm one of those myself. The reasons for my opposition to the widely accepted understanding of rainbows are many, but relatively simple. One of those reasons for example is concerned with the mainstream belief that the size of the raindrops is fundamentally responsible for the visible appearance of rainbows. And of course, it is basically visible appearance that differentiates the exotic twinned rainbows from the ordinary ones. Let me give you one concrete, quick and good example about how that connection was made, and about why I refuse to accept it as a given. Have a look at the screenshot below.

A careful assessment of the commentary, coupled with an equal degree of visual observation of the two pictures, should hardly deter anyone from seeing how tenuous the persuading argument is. In fact, I believe that it's so tenuous that it will more than suffice on my part to just point direction to a handful of the most relevant factors in the issue, leaving therefore the final conclusion entirely to your own discretion.

In full consideration of everything said, why couldn't it be that in the upper picture the rainbow appears narrower and with more intense colours due to the higher density of drops per area than that in the lower picture? In other words, what do you think would happen if we could take the same amount of water drops that forms the bow in the lower picture and compactify it within the area shown by the upper bow? After all no one needs a Ph.D. in physics to see that the bow in the lower picture is broader because in the time between the two shots the water drops had travelled some distance toward the ground, extending in the process the area illuminated by the sun, where in effect the rainbow is created. Pay close attention to the sprinkler jet in the two pictures and it shouldn't be very hard at all to realise what a short time was between the two shots, and at what points the two bows were consequently recorded. Compere then your own reasoning to the explanation given and do not be afraid to ask what on earth could "the sprinkler's drops were largest near the main jet and they produced the narrow colourful bow" really mean and signify in the whole context. Look at the appearance of the bow in the upper picture all along its length and then ask again the previous question. Finally, have a good look at the corner of the building towards which the sprinkler is rotating and compare the shadows of the trees visible on the brickwork in both pictures. Notice the difference? Of course you do. What do you think caused that difference?

If you read carefully the commentaries in the pictures of twinned rainbows that I showed you earlier you must have noticed that there was a significant deal of scepticism about those flattened raindrops being the real cause of twinning. But that scepticism has been eradicated from the conventional belief ever since those computer simulations were created, and along with it all those former issues of concern have been treated in the usual manner (which is a manner so well known that there's no need of me to spell it out aloud for anybody, surely). Nonetheless, in spite of those former concerns being put to a convenient rest, there is another crop of inconvenient ones that are yet to be dealt with (in whatever form). Let's have a look at the picture below.

Here we have a good picture of a twinned rainbow, and by using this example as a first yardstick we can immediately notice that something is not quite right between this piece of evidence and the conventional wisdom.

So, according to the accepted understanding of the rainbow phenomena the upper bow in a twinned rainbow is created by small raindrops (somewhere around 0.3 mm in size, apparently) while the lower bow is created by significantly larger raindrops (varying in size, apparently, from drops with a 0.4 mm radius to those of 1 mm, and more). Furthermore, according to the accepted understanding small raindrops produce broad and kind of pastel-coloured rainbows, while big drops produce narrow bows with much more intense colours. Now, taking all these points into consideration we can see that the picture above agrees with the conventional wisdom only 50%. In effect, from the picture the conventional understanding can only claim to provide an explanation for the widths of the twinned bows, not for their colour intensity. And the same state of affairs is evident in the pictures below, as well as in three of the four pictures of twinned rainbows I showed first on this page.

In the case of the fourth the situation is even direr, for in that picture the conventional wisdom cannot account for either the bows' widths, or colours. (See below.)

So, what creates twinned rainbows in my understanding? Having explained in the first part of this post what factors enabled me to cast the image of a twinned bow on a screen I can now answer that question in just two words: Cloud configuration.

Specifically, in my understanding twinned rainbows can be formed if the sunlight's path toward the falling rain is restricted to a cloud configuration similar in shape to the structural configurations of the flashlights shown in the first part of this post. See the image below for a (quite ordinary, I admit) visual depiction.

Although the cloud configuration depicted in the picture is basically the only one that is necessary to account for the twinned rainbows, in reality there are many more slightly different configurations that could facilitate the apparition of other kinds of twinned rainbows. Nonetheless, all the twinned rainbows that could possibly be created by different cloud configurations will always have one fundamental aspect in common: A tunnel-like cloud configuration. The particular shape of that tunnel configuration may be different at times (for example in some instances the tunnel may be conical in shape, or in other cases it may be symmetrically tubular for their entire length) but all those differences in the cloud configurations will in the end create pretty minimal differences between the eventual twinned rainbows that will be formed. Let me show you a few pictures to illustrate visually what I've just said.

I can tell you that in the last few weeks that I had been silent on these pages I experimented quite extensively with different structural configurations that in the end gave rise to many different twinned bows, but I can also assure you that those differences were in the end measurable in degree, not in kind. With one major exception, though. Which is the one I'll drop below now.

What you see in this picture is a triple-split bow, which as part of the rainbow phenomena is even rarer than a twinned bow. In fact, much rarer, since it appears (to the best of my knowledge) that there have only been two such rainbows ever photographed in reality. One of those two took place in 2012 in Japan, and below I'll show you a copy of one of the photos taken on that occasion. For a comprehensive description of the triple-split rainbow in Japan you can go here.

Now, in order to prevent a possible (but totally non-relevant) objection to the previous image I had named as a triple-split bow (e.g. "your image of what you called a triple-split bow doesn't look anything like the image above!") let me show you next another image of a triple-split bow, which I created with a different LED flashlight.

Nonetheless, the reality is that it was the same set of flashlights that I used to make both the twinned bows as well as the triple-split ones. Not only that. On a couple of occasions, I transformed two flashlights that could not produce twinned bows into ones that managed to achieve that feat. (See the image below, and you'll know exactly what I'm talking about.)

Finally on this subject, I would like to show you a few pictures of some real twinned rainbows that appear (to my mind, at least) to give credence to my understanding of what causes the existence of twinned and triple-split bows. Have a good look at the pictures below then, and without any additional commentary on my part think about why I believe that they do so.

Last word

The subject of rainbow making is impossible to comprehend if you try to make sense of it based on the information we have been fed in the last four or five centuries. Any reasonable mind should be able to see that by contemplating from a quiet corner the stories on the subject that have been spun around by the conventional scientists and swallowed without any questions by the rest of the world. In fact, any reasonable mind should realise that simply from observing how every time the conventional story is confronted with some evidently pertinent question the answers given in reply are suddenly delivered in gibberish or spoken in tongues. Let me give you just one concrete example that so is the case from amongst the myriad that are out there.

Having listened and understood everything you have said about rainbow formation, could you (Dr. XYZ) explain to me how the colours refracted from the sprinkler drops marked by me in the picture below have arrived at my eye? Would you be kind enough to ray trace their entire journey from the sun to my eye, please? Thank you.

That's all for now. Hooroo.

Making sense of the elusive twinned rainbow (in the lab, and in reality) Part 1.

Last week I managed to cast on a screen the image of a twinned rainbow.

It was a somewhat accidental act, but then, in a matter of minutes I learned  how to do it over and over again, first time every time, without fail. That was so because the entire process (from the theoretical one to its practical counterpart) is so simply and straightforwardly coherent that in just about anyone's mind everything about it is instantly accepted and accommodated. Let's see next if you agree with me about that.

In all my images of rainbows that I have thus far produced I used two kinds of tools: a number of different LED flashlights, and three glass balls of different sizes. The flashlights (which ranged in power output from perhaps a mere 4 or 5 lumens to a mightily blinding 600) were basically of two different kinds again. One of those had either the LED emitting freely and directly from the front line (so to speak) or otherwise from a 'back' line (if you will) due to an all enclosing hood. (See picture below for a much more eloquent depiction, please.)

Now, let me say this right away: these types of flashlights will not produce an image of a twinned rainbow. In order to get an image of a twinned rainbow a flashlight of the either type below is an absolute necessity.

The LED of the flashlight on the left is situated at the back of an ellipsoidal chamber, which is divided into two unequal parts by a circular kind of wall. The LED on the right is situated at the end of a truncated conical reflective surface.

And now, with everything above being hopefully clear, let us create an image of a twinned rainbow.

There is no need of me to tell you anything about angle of incidence, just as there's no need for you to try to orient your light at an angle as close as possible to the one in the picture, by the way. You will get an image twinned at the top from just about any angle, other than one running perpendicularly to the glass ball. The only difference you'll see with every new angle will be the points where the twin bow merge with the primary bow. (See the examples below.)

If you position your light to shine perpendicularly to the glass ball, on the other hand, you will no longer get an image of a twinned rainbow but the image of what should be called a twin rainbow, instead. (See below.)

⏳

The first clue about how an image of a twinned rainbow is made comes very simply from an observation of the glass ball. Look closely at the photos shown below.

Look at the two overlapping caustics in each picture. Both of them are pointing in the same direction (red end forward, blue end backward).  That means that they are related and originate from a common source. The broader, well-defined and properly aligned one is responsible for the primary bow; the narrower, misaligned one is the generator of the twinned bow. Normally at that point there should be only one caustic present--the primary one. What is the cause of the twinned caustic, then? The answer to that question is easily extracted from the two pictures below.

The first picture shows the fields of light generated by the two types of flashlights I had shown you earlier and specified that they can't produce images of twinned rainbows; the second picture shows the fields of light that are typical to the two types of flashlights, also shown earlier, that are capable of creating images of twinned rainbows. You can extract the answer we were looking for on your own now.

A close inspection of the glass ball has become an absolute norm for me, and now I want to show you what an amazing catalogue of information is always on display for an observer's hungry eyes.

This is a view of the glass ball's back. Notice the copy of the twinned bow in the inverted image at its centre. Behind it there's the secondary bow, and in between is Alexander's Dark Band. The most amazing thing about that secondary rain-bow I never seen being discussed, or even mentioned, by any mainstream physicist. The most amazing thing is the sheer fact that this particular rain-bow is both a primary rain-bow as well as, equally, a secondary one. It is a secondary one from this perspective, and a primary one if you look at it from the other side--which is usually dubbed the front of the drop. It is also the one that's casting the image of the rainbow on the wall. I said 'also' for very good reasons, which for here and now I shall leave unmentioned.

In the picture above notice the three bows displayed at the centre of the glass ball/drop, although the image on the wall is that of only a twinned rainbow. There is a very good reason why not a tripled rain-bow is cast on the wall, which is visibly manifest in the maximised picture below.

Look closely at the secondary bow.

Self-explanatory.

That's all, for now. Come back next weekend sometime, though, and I will share with you the second part of this new saga.

Hooroo.