NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: horizon visibility puzzle
From: Victor Reijs
Date: 2001 Jun 22, 5:28 AM
From: Victor Reijs
Date: 2001 Jun 22, 5:28 AM
Hello Aubrey, I have some javascript for this: http://www.iol.ie/~geniet/eng/refract.htm#sea I you use for local height: 777 m and for distant height: 401 m and distance between the two 35 km You see that the apparent altitude of the distant height is -0.73� The sea is from the local hill is: -.79� So the sea is not visible! If we decrease the distant hill to 366 m, the sea becomes visible. All the best, Victor P.S. I am using formulas from Thom (see the text in the page). Aubrey O'Callaghan wrote: > > Basically this is a distance to horizon problem: > On the 777 m hill you can see: > 1.144 sqrt( 777*3.281) = 57.76 n. miles > On the 401 m hill you can see > 1.144sqrt(401*3.281)= 41.5 n miles > now hills are 35 km apart 35/1.8=19.44 n. miles > > If 777 and 401 m hill were at same place the difference in distance viewed > would be 16.26 n miles > If we move 401 m hill forward 16.26 n miles we can both see the same point. > Therefore this is the line cutting both top of both hills to horizon. > But we have moved it forward 19.44 n .miles so 401 hill will block 777 hill. > > We cannot see the ocean from 777 hill due to presence of 401 hill. > > Aubrey. > > At 03:17 PM 20-06-01, you wrote: > >You are ashore, 777 meters above sea level, looking toward the ocean. > >In your line of sight, 35 kilometers away, is a hill 401 meters high. > >Can you see the ocean over the top of this hill? > > > >This is an actual question someone has asked. I've come up with an > >answer, but am curious how others might solve the problem. One person > >approached it from a completely different direction than I used but > >got the same answer. > > > >-- > > > > > >paulhirose@earthlink.net (Paul Hirose) -- URLs: http://www.iol.ie/~geniet http://www.iol.ie/~geniet/eng/archaeocosmology.htm http://www.iol.ie/~geniet/maeshowe http://www.iol.ie/~geniet/setrise http://www.iol.ie/~geniet/irishstones http://www.iol.ie/~geniet/stpatrick