Galileo and Weather

BooksOn my recent trip, I was able to read on the plane a lot of Galileo’s Daughter — a fascinating account of his whole kerfuffle with the catholic church, framed by correspondence from his daughter (who he had placed in a nunnery, because she was illegitimate and he didn’t believe she was fit for marriage).

At the center of said kerfuffle was his argumentation for a Copernican worldview.  One of the big questions in that debate was, if the Earth is spinning, why does it seem so stationary?  How can anything drop straight down?  How can birds navigate? Why isn’t there crazy wind all the time?  Galileo had good answers to all of these questions, but I wondered why there was no mention of the fact that wind does prevail in the same direction almost all of the time?

One tiny little adjustment I have had to make between living on the west coast, and then the east coast, and then the midwest, and then England, and then the west coast again, is orienting myself with local weather maps.  I grew up being used to having ocean on the left, land on the right.  Then it was vice versa.  In Ohio, there was lake to the north (the “North Coast”).  And in England, I was on an island.  But one constant in all those places — weather always comes from the west!  The only exceptions (like arid Santa Ana winds blowing westward over San Diego from the desert, or vicious “Nor’easter” storms coming from the North-East (from the Atlantic)) serve to prove the rule.

I’m sure Galileo and his opponents were aware of this near perfect rule; but perhaps Galileo never exploited it, because he didn’t have an explanation for why weather moving eastward would seem to imply that the Earth’s atmosphere is rotating faster than the earth — it would be much more straightforward for the atmosphere to be lagging behind the rotating earth, which would be trying to drag it along.  What could make the atmosphere rotate faster than the planet?

I think this is due to our location well away from the equator.  At the equator, the atmosphere does indeed lag behind the earth’s rotation (as of today, this satellite weather video shows weather in Uganda traveling westward).  But as that traveling-eastward-but-not-quite-as-fast-as-the-earth equatorial atmosphere deviates to the north (or south), it ends up over earth which is going around not as fast as the equator (since at higher latitutes, the “all the way around” the earth is not as far as at the equator) — and voila, the atmosphere is now going “faster” than the earth!  It’s like a 5mph treadmill going through water, and only making that water move at 4mph.  But then that 4pmh water gets diverted to flow over a 3mph treadmill, so it is suddenly faster.

So, anybody know if I am right about how our atmosphere could possibly be rotating faster than the earth itself?  Or anybody know whether Galileo uses the unidirection of weather as an argument in his Dialogues?

One Response

  1. I’ve invited my personal meterologist, a fellow teacher who missed his true calling, to this thread. On my own I’d guess it has to do with the eddies you see in globes set up at museums to demonstrate the movement of gases around planets, with the temperate areas (San Diego, Baltimore, London) being right in that range where the eddies curl up and around (forward/eastward). But I’m sure my friend will have a more convincing response.

    You caught my attention with the Kampala weather. What a long time ago that was.

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