Naturespeak A naturalist's view of the world

May 31, 2008

Sun Worship

Filed under: Uncategorized — wykes @ 8:14 am

   On a recent chilly morning with temperatures hovering in the middle 50’s, I came upon 10 sunning Painted Turtles. I guess you could call such an assemblage a herd or even a flock of turtles. I think a shellage might be a better term – or how about a palette. Yes, a palette of Painted Turtles sounds nice. Anyway, this particular palette of painters was participating in the pursuit of power: solar power.

  Like all cold blooded creatures they require the warmth of a star some 93 million miles away to jump start their internal engines.  Painted Turtles are well adapted to northern climes. They hibernate through most of the winter, but will swim under the ice on occasion and are able to get around on very cold early spring days. A 50-some degree day is relatively warm for such a beast. On this day, the turtles were drawn to an open spot in the marsh where they could take full advantage of old Sol. Each was hauled out onto a pad of cat-tail roots or a clump of low vegetation. What was fascinating, in terms of this discussion, was that all of them had oriented their shell surface in the same direction and all were positioned at about the same angle.

  It is no surprise that their shells were oriented toward the low southern sun (see here). They chose the mid-morning period just as the golden rays were peeking over the shadows cast by the cat-tail tops. The fact that they were oriented at the same angle was no coincidence, however. This angle was about 40 degrees.

  I know this not because I have an eye for angles – for I am not an angler (that was a joke). The skittish turtles, would not have allowed me to measure them either. No, this happens to be the golden angle for maximum solar absorption at our latitude (that was not a joke).

  Allow me to present another example of this natural solar knowledge. Wood Ants construct large angled nests out of soil particles (see here). These ants work together as a group to maintain their roof at an angle that picks up the heat from the low morning sun when they need it most. Since they can’t constantly adjust to the sun’s changing position, they instinctively choose the best general angle. I was able to measure this angle since ant hills don’t scurry away at the sight of humans. Sure enough, the angle was about 40 degrees with a southward orientation.

  When we peoplekind put up solar panels, we are generally instructed to place them so that they face south and have a “tilt about equal to your latitude.” Our local latitude is about 42 degrees from the equator, by the way. More specifically, the optimum angle recommended for our position on the earth is closer to 40 degrees during the spring and autumn. The summer angle is about 12 degrees lower.

  Summer conditions require a lower angle because the sun is higher in the sky. The turtles will oblige by lowering their shell angles to about 25 degrees when that time comes but the ants will be happy with what they have. I hope you’ll be happy knowing how energy smart turtles and ants really are.

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