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Nice. Thanks for the link! That's a fun demo... but why not just have a supersonic jet fly by at 100 meters altitude once every 15 minutes? If you wanna make a point, you gotta do it with a bang! ...and a big carbon foorprint for maximum effect! Maybe next year?

More seriously, I feel it's very difficult to drive home the concept of the enormous angular momentum and the colossal rotational energy of the Earth's seemingly delicate spin on its axis. Nobody believed it when Galileo advocated it. Why isn't there an enormous wind blowing all the time?

In our early school years, we learn that the Earth travels around the Sun keeping its spin axis pointed in the same direction (pointed essentially towards the North Star for the whole year) while it orbits around the Sun. Thus during half the year the northern hemisphere is facing more nearly towards the Sun while during the other half, the southern hemisphere gets the heat. Ta-da... now we know why the seasons happen. But do we? Where's the why? The missing element here is the explanation for the Earth's nearly constant axial orientation. Why shouldn't it just precess as it travels around the Sun so that the northern hemisphere gets summer all year (and the climate thus collapses) or at least for some indeterminate multiple of a year? The standard grade school explanation doesn't really explain it, right?

Of course in later years, if we study enough celestial navigation or astronomy, we learn that the Earth does not keep its axis pointed in a fixed direction and instead it wobbles about in a nice clean precessional circle every 23,000 years or so. And then still later we learn that there's nothing so clean about it, and the precessional motion actually includes changing axial tilt and other evolutions ...and the climate collapses after all [see attached image].

But the key component in all these things is that enormous angular momentum and rotational energy. It's very hard to make the Earth wobble!

Let's consider energy since it's more familiar. The rotational energy of the Earth is around 2·10²⁹ joules --which, without context, is a meaningless number. Obviously, that qualifies as "a lot" with that big exponent on the ten, but how does it compare? The Earth is bathed in sunlight. If we could capture every single joule of incident sunlight, how long would it take to match the rotational energy of the Earth? I did this "back of the envelope" (quicky spreadsheet) just now and found roughly 160,000 years. That's every last photon of solar energy for over a hundred thousand years. That's a lot of energy! Or how about in human terms... The energy consumption of human civilization globally today is something like 600 exajoules annually (6·10²⁰ joules) which means that the Earth's rotational energy is equivalent to about 300 million years of civilization's current energy consumption.

Now how can I make a desert-party stunt out of all that?! :)

Attached below is a famous 1982 "Far Side" cartoon by Gary Larson. If the Earth wobbled a little less, we wouldn't get these annoying walls of ice sprouting up in our backyards every 50,000 years or so... Maybe we should tap that vast rotational energy and angular momentum, after all, and get this defect under control!

Frank Reed

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