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Old 12-16-2020, 06:00 PM   #11
Join Date: Sep 2007
Default Re: Can the hydrology of this world be made to work?

Originally Posted by Michael Thayne View Post
What do "east" and "west" even mean independent of the planet's spin?
Not what I meant. Simply that if you spin the planet the other way around, it's the same as reversing the map east-west. The labels would also change (assuming the inhabitants find sunrise and sunset interesting), but the actual relative geography doesn't. Either the mountains are spinward of the river or they're anti-spinward.

Prevailing winds are a result of the Coriolis effect. Reverse the planet spin and you switch the direction of the Coriolis and thus prevailing wind direction relative to geographic features. Or you could flip the relative positions of the rivers and mountains (flip the map) while keeping the same rotation direction. Only if you do both reverses does the situation remain the same.

Assume the mountains start off antispinward of the rivers; other factors are such that prevailing winds come over the mountains so the rivers are in a dry region. Now, flip those mountains to spinward of the river. The planet's still spinning the same way, so the wind moves the same way, but now the wind crosses over the rivers first, then the mountains. Not dry. Now do the second flip, this time of the planet's spin. Now the mountains are antispinward of the river again, so the rain shadow is back. Either change alone will reverse your prevailing wind direction relative to the geography. Both together means no net change.

It doesn't matter to the existence of the rain shadow if the inhabitants also switch their words (which I agree they probably would, if they find sunrise as interesting as humans do), because that linguistic change doesn't flip the mountains to the other side of the river along with the planet spin or cause the wind to prevail in a different direction. The label is not the terrain.

But this point is really off in the weeds. The practical upshot is that it's merely a way you could save an existing map, assuming you had one already drawn and didn't want to redo it. (Or you scan it into Photoshop and reverse it left-to-right.) Or perhaps you want to save existing text that's chock full of references to this being "east" or "west" of that, and it'd be a chore to edit all those words to match changing planet spins.
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