Some things are just fun to tell

So, here is another forward light scattering piece. I'll start with a question. Why is the morning mist that rises from a good microbially-cooked, mature manure-pile more vigorous when viewed from the shady side of the manure pile than from the sunny side of that early-morning dung-heap? Clues are in the green cloud story. Forward scattered of light is brighter than back scattered light. In forward scattering, the light waves remain in phase after the scattering. In back scattering, the waves of photons are at a wide range of phases. Interference cancels out some of the light and it is all rather dim. So, we have the rising, ripe mist of sweet smelling scents coming from the putrid pile of piloblis substrate for all to see. It is a place you can get in touch with your feelings. The mist scatters the light and we see it as a diaphanous mist. If it didn't scatter the light (remember it scatters all wavelengths because the mist drops are big relative unlike blue scattering haze particles) the emanations from the pile would be transparent and I would never have needed to talk about all this. To get yourself all squared-away on brightness of light scattering try the following. Wait until summer comes and it is about one hour after sunrise. By that time turpines and hemiturpines are fresh from the early morning photosynthesis and a blue haze of the early day begins to develop. Look toward the sun and see how bright the haze is in the forward scattering direction. Now put on your tutu on, begin a slow pirouette and notice that the haze is least bright when the sun is at your back and the haze is seen only from backscatter. So, you want a real puzzle. Get your polarizing sunglasses on without getting out of your tutu and then do the same haze-viewing, slow pirouette. Is there any difference in the haze brightness by this new method? Biogenic haze when the relative humidity is less than 65% scatters and polarizes light. Now that is tutu much of a challenge for the curious scientist.

Photo: Photograph © Andrew Dunn,, Creative Commons Attribution-Share Alike 2.0 Generic


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