Quote:
Originally Posted by dcarson
OK. Horizon is sqrt [ 2 x radius of planet x height above surface + height above surface ^2]
So using 3390 km for radius and 7 km for height of the walls the horizon is 218 km. The canyon is 200 km wide so you can see all the way across. That is using max depth. If parts of the canyon are only 3 km deep you can't see either wall from the middle. If it is less than 6 km you can't see both. Which may be what I'm misremembering.
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Putting your formula into Excel, I agree with your 218-km horizon for walls 7 km high. But at 5 km the horizon is 184 km, which means you'd have to be within 16 km of one wall to be unable to see the other. If by "the middle" you in fact mean "halfway between the walls," each wall is 100 km away, and even 2-km walls give you a horizon of 116 km. The effect seems much less extreme than you're describing, unless I'm doing something wrong.
Too bad; it was a pretty image.
Bill Stoddard