Too nice a morning here to spend indoors blogging, so I'm heading out for lawn chores. In the meantime, enjoy this photo of Blue Morphos.
Many morpho butterflies are colored in metallic, shimmering shades of blues and greens. These colors are not a result of pigmentation, but are an example of iridescence through structural coloration. Specifically, the microscopic scales covering the morpho's wings reflect incident light repeatedly at successive layers, leading to interference effects that depend on both wavelength and angle of incidence/observance. Thus, the colors appear to vary with viewing angle, but they are actually surprisingly uniform, perhaps due to the tetrahedral (diamond-like) structural arrangement of the scales or diffraction from overlying cell layers...Addendum: As noted by reader Bill in the comments, this photo is likely staged. Blue morphos, like Mourning Cloaks and other woods/forests butterflies, have colorful topsides to their wings, but have camouflage patterns on the underside, so when resting they would sit with wings folded up. They would flatten the wings to solarize/absorb heat - but in this image only the topmost of the group are in the sun. This image was either generated with an image processor, or perhaps is a picture of a diorama in a tropical visitor's center or natural history museum.
Whatever the true color, the picture is breath-takingly gorgeous!ReplyDelete
People stumble over this kind of "colored but not colored" discussion. But lets cut to the chase. If something looks blue is is by definition Blue. And if it looks Blue under "white" light then this is absolutely true. It's blue.ReplyDelete
By this I mean the light entering your eye are photons register as blue spectral content. That's the only definition of blue. it reflects or emits blue light.
Now how did the white light become blue. That's just a question of mechanism. There's two extremes one is the light is not absorbed but dispersed spectrally. (transmission would be special case of dispersion.) So red goes over here and blue over there. The other is all but blue is absorbed.
The tricky business happens here. Why was it absorbed. One reason is that the chemical absorption absorbs the red directly and selectively. The other is the red light is scattered internally many more times than the blue. Because of the many reflections each of which has some chance of absorption at all frequencies the phtons are absorbed. SO more refelections means more absorption of red. THis last sort of case leads to the interesting result that if you destroy the structure of the material the selective reflections are removed and so it's no longer blue. It's this effect that make people say it's not really blue.
but no it's blue. Whether it's chemically selective absorption or structurally selective absorption it's still more blue light being sent out so it's blue.
In fact for a lot of cases it's the same variable in the equation epsilon (the dielectrice constant). Absorption comes from the imaginary part of the dielectric constant, and light dispersion comes from the magnitude (real and imaginary part) of the dielectric. So even at a physics level, the structural and chemical aspects of this are the same origin.
Just for the sake of discussion... is it blue in the dark? Or would it just be "potentially blue?"Delete
Bishop George Berkeley would be proud of that question.
And Mr. Strauss gives us the philosophy of pragmatism.
I think that photo might be staged for a few reasons. 1. a bunch of male Morpho menelaus congregating like Monarchs 2. there's only 1 with his wings folded, they all look mounted.ReplyDelete
In retrospect I quite agree. Their camouflage is on the underside of the wings. I've amended the post accordingly. Thanks.Delete