Hey, first post here. This forum looks like fun, from what I've seen, as long as you don't take it too seriously (cpt bthimes, or whatever it was). Anyway, assuming you got your 20 mile figure from that webpage on the lighthouse, it says the LIGHT is visible from 20 miles, not the lighthouse itself. Of course, if you are asserting that YOU can see the lighthouse, or any part of it, from 20 miles, by personal observation, that's obviously different. That puts you in the Tom Bishop (he seems like a fun guy!) class, and you would have to prove that assertion. Note that proving mathematically that you should NOT be able to see it does not equal proof that you can. That still only leaves your assertion.