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Battlemage

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  1. I know this is an older thread, but I thought I'd give a solid theoretical answer to this question based on some over-estimating assumptions. Given the curvature of the earth, you can use geometry to find the maximum distance for which you could see lightning. We can use the following formula: d = (2RH + H2 - 2Rh - h2)1/2 where H is the height of the clouds, d is the distance, h is your height, and R is the distance to the center of the earth. This formula makes the assumption that the earth can be approximated as a sphere, and it assumes that the angle between your line of sight to the lightning and the line from the center of the earth through your body is 90 degrees (a reasonable assumption since the earth is approximately flat over short distances). My use of the formula assumes the topmost cloud layer is 49,000 feet high (based on wikipedia's info on the height of clouds from which lightning originates), the distance to the center of the earth is about 4000 miles and the height of the observer is 6 feet. Using those numbers, the approximate theoretical furthest distance you can see lightning from is: d = (2*4000 miles*49,000ft + (49,000 ft)2 -(2*4000 miles*6ft) - (6 ft)2)1/2 ≈ 273 miles. So there you have it folks ;). In theory you could see lightning from a lot further away than what everyone was guessing. Of course, these assumptions make this the MAXIMUM POSSIBLE that you'd be able to see just the top part of it, and that's assuming that you even see it at it's origin point. So this is probably an overestimation. But at least we can be confident that the limit is about from this distance. *as far as accuracy for these estimations, before I did this I also did a more simplified calculation in which your height was zero, which gave the formula d = (2RH + H2)1/2. This formula gave 272 miles, so you can see the other terms that depend upon your own height don't really matter. Regardless, this is an estimation, but you can see that it's on the order of 2.5 to 3.5 hundred miles. If you use the law of cosines and solve for that distance, the angle differing from 90 degrees by 1 degree or so makes a difference, but really, 90 degrees is a solid estimation given the large distance, since the replies in this thread give values ranging of around 150 miles, which would correspond to an angle of about 92 degrees rather than 90. So I think an assumption of 90 degrees gives a reasonable guess for the MAXIMUM distance you could see.
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