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# Structural Coloration: From Blue Jays to Butterflies, find out how colors can be based on nanostructures instead of…

Structural Coloration: From Blue Jays to Butterflies, find out how colors can be based on nanostructures instead of pigments.

Originally shared by Tom Eigelsbach

Researchers are working to understand how often-colorless biological nanostructures give rise to some of the most spectacular technicolor displays in nature.

So what do the feathers of blue-jays and peacocks, the blue eyes of some gorgeous women, the opalescence of some gem stones, and the blue sky above us all have in common? Math. Because none of them are actually blue: rather, they are all colorless, yet they scatter blue light but not larger wavelengths of light. Rayleigh scattering in the sky, and Tyndall Scattering in blue feathers and eyes. How does this work, exactly? With a delightful mixture of microbiology and physics.

The formulas have an inverse fourth power dependence on the wavelength of the light  (λ^−4), which in English means the red and blue ends of the spectrum get treated differently, with the blue light being scattered, unlike the red light. Which accounts for why our sky is blue and not red or yellow or white, for instance. You can also see Tyndall scattering if you have friends who ride motorcycles: look for blue smoke spewed from them; the particles are provided by burnt engine oil, and they also scatter only the blue light.

But it’s much more unintuitive in feathers and eyes, because we know that pigments tend to cause coloring in animals, and they do for most other colors of feathers, for instance. But not for blue feathers; and not for the colors in the irises of our eyes. Blue feathers and eye colors are called “structural colors” because they are generated by light interacting with the 3-D shape of the colorless material, as opposed to a colored pigment or dye, which simply selectively absorbs some colors and reflects others. Note that pigments and dyes fade (think of your old blue-jeans or tie-dyed shirts that have faded). Structural colors, on the other hand, can easily last for hundreds or thousands of years or more in the feathers after the animal has died.

With blue feathers, blue-jays and other blue birds as well have no blue pigment at all of any kind in their feathers. Rather, blue-jay feathers consist of extremely small specialized cells. As the feather grows, keratin elongates in the cells and separates from water. Then when the cell dies, the water evaporates and the keratin forms permanent, honeycombed, sponge-like structures, called “barbs” in blue jays. These structures absorb the red end of the spectrum and scatter and reflect the blue end, thus making the blue-jay appear blue to us.

In our eyes, the colored part, the iris, is composed of two cell layers: the front stroma layer; and the rear epithelium layer. The stroma consists of colorless collagen fibers. The stroma only occasionally will contain brown melanin pigmentation, but sometimes is totally colorless, containing no melanin. When this occurs, and the stroma is colorless, we have blue eyes, because when light enters the eyes the blue light gets scattered and reflected back out. This also accounts for the variations in the shades of color of someone’s blue or green eyes, depending on the lighting they are in.

Article on eyes:

Article on Rayleigh scattering in the sky:

http://math.ucr.edu/home/baez/physics/General/BlueSky/blue_sky.html

Article on the why the Martian sky is Pink, and not Blue:

http://www.doublexscience.org/everyday-science-why-is-the-sky-pink/

Article on blue feathers below.

#scienceeveryday   #sciencesunday   #physics   #microbiology

## Join the Conversation

1. Microstructures.

Anywhere you see those iridescent colors in nature.

3.5 billion years of trial and error are on display around you.

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2. It is pretty amazing that all this design happened without a designer, I guess I just don’t have enough faith to believe it all happened by accident!

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3. Natural selection is not accidental. The word selection underscores that factual and proven aspect.

Great post!

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4. Bruce Budrick you don’t need faith to understand and appreciate how evolution works. Reading, observing and investigating the natural world around you is all that you need 🙂

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5. Fabulous article; thank you for publishing a very comprehensive abstract

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6. The structure that creates the appearance of eyes on the feathers of a peacock is beautiful and I give God glory for his creation. When you look at everything through the lens that there is no God you have to invent other explanations for how the dna was created. The assumption that millions of years is like magic and anything can happen if you give it enough time is ridiculous.

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7. Bruce Budrick – billions. There is no “accident”, everything you see around you in the biosphere is the result of billions of years of struggle to adapt and survive.

Every cell in the biosphere and your own body is constantly monitoring it’s environment and responding to it.

There have always been those fundamental questions, ever since we could think. There was no explanation available, so our gods were created to answer those questions – before we understood what an atom was or where the Sun went at night.

With no understanding of lightning, it’s easy to see why “a god” must be responsible for the terrible power that lit the sky and the rolling thunder of his anger.

We now understand the nature of lightning, how and why it forms, we can quantify the voltage. We know thunder is a result of super heated air expanding and breaking the speed of sound.

No angry god there.

Today, no one has a problem relegating the Greek, or Roman gods to mythology, but when it comes to their god it’s somehow different.

“Gods”, one or many are all a reflection of our ignorance, and the innate understanding that there must be a reason for this. With a lack of knowledge to explain everything, gods were a natural to fill in the blanks.

” The answers have been there all along- we just couldn’t read them.” – Cosmos

Evolution is a lot more plausible than an omnipotent creator waving his hand… And why would a loving god create a world where the animals have to eat each other?

Being thrown out of the garden of Eden doesn’t fill that blank for me.

The impulse is to flatly deny what we don’t understand.

Learning is the key.

I lean on science as opposed to theology because science requires you to tear it down if you can. Theology threatens eternal damnation if you question it.

Which system is more likely to provide the answers we seek?

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8. Schopenhauer will.

And in greek Zeuz means ” DESIRE”.

No blind objectives, but an incredible efficien feedback.

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9. Doesn’t science look at every possibility? Why do many science students automatically start with there is no intelligent designer that created all this design? If you left that possibility on the table and look at the evidence again you may see everything from a different perspective and see the truth of the evidence. But no, you start by saying there is no creator so let’s look at how we can explain everything without a creator. Your perspective is flawed to start with and not true science that looks at everything from all angles. Suppose there was a global flood on the earth, what would the evidence show? You might be amazed how it all starts to make sense when you look at EVERY possibility…unless you have a personal problem with god that blinds you from seeing the truth. Your perspective produces a different result looking at the same evidence. By the way, a theory is not a proven fact.

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10. David Andrews if u don’t believe in God can you explain what happened before big bang

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11. Mai Daly no, I can’t, science has no evidence – but I will refrain from trying to explain it by crediting a myth that has no supporting evidence.

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12. David Andrews so u believe that science have no answer to every question and I think it will not have . Every answer the science find open new infinite number of questions . And our problem is that we think that we can know every thing with our limited abilities . And if we are here from million year ago or maybe less and only reveal from my opinion 1% or 2% from nurture secrets or may be less I don’t know. And the hidden is greater . Our ego prevent us from admitting that we are only creatures with limited abilities and only creator our God who create all of this only him has all answers and by saying that universe come from no thing . We just humiliate ourselves . And Every thing of this life will have no meaning. I believe in science but my believe in science increase my believe in God .

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13. Mai Daly Good point.

“The more we learn, the greater we find is our ignorance”

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