Look Up from Beneath a Tree! The Secret of the “Hands” That Gather Light
Hi, I’m Ken Kuwako, your Science Trainer. Every day is an experiment!
Have you ever looked up at a tree from directly underneath? Next time you get the chance, lie down at the base of a tree and gaze up at the sky. The branches split and spread, and at the tips of them are the leaves. It looks like a giant hand stretched out to gather up the light.
Look at that fractal structure!
The Secret Behind How Branches Split: Fractals
Look closely at the photo. A thick trunk divides into branches, those branches divide again, and they keep going until they become tiny twigs. When the shape of the whole thing looks a lot like the shape of its parts, we call it a fractal structure.
Fractals aren’t just a tree thing, either. You can find similar patterns in things all around you: a floret of broccoli, a fern leaf, the course of a river, even the bronchial tubes in your lungs. By branching again and again, you can pack a huge number of tips into a limited amount of space. For a tree, it’s a clever way to catch as much light as possible using as little material as possible.
“Gimme Light!” … But They Also Take Turns
It almost looks like every leaf is shouting, “Gimme light!” But look more closely and you’ll notice that the leaves barely overlap each other.
There’s a good reason for that. If an upper leaf casts a shadow on a lower one, the lower leaf can’t photosynthesize properly. So plants stagger their leaves to make sure every one of them gets its fair share of sunshine. In many plants, each new leaf around the stem is offset from the previous one by about 137.5 degrees. This number is known as the “golden angle,” and it’s closely tied to the Fibonacci sequence. The same family of numbers also shows up in the arrangement of sunflower seeds and the pattern on a pineapple. Pretty amazing, isn’t it?
Fractal Shades: Another Idea Borrowed from Nature
I once served as a scientific advisor for a TV program that featured fractal sunshades. A good sunshade doesn’t just block the sun. The best designs let some wind pass through while still keeping the light out.
If a sunshade were one solid sheet, it would catch the wind and be easily blown away, and the heat would get trapped underneath. But if it’s full of gaps like the leaves of a tree, with shadows of different sizes overlapping, the wind can slip through and you still get cool, comfortable shade. The shade of a tree also feels refreshing for another reason: as water evaporates from the leaves, it carries heat away with it. There’s so much we can learn from nature!
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