Range of Visibility

[ossian]

Recently I was on top of Benbradagh (~1510 ft.) just outside Dungiven in Co. Londonderry, N.I. and looking roughly NNE I could see the Paps of Jura about 70 miles away. Behind the Paps of Jura, in the far distance and in the same direction , I could see another mountain (s). Checking my atlas it appears that this mountain is Ben Nevis (4409 ft). Can this be so as Ben Nevis is approximately 140 miles from Benbradagh?

Stewart

[jomifl]

Use the link below to calculate the 2 height to horizon distances and add them. It seems to be just possible
http://www.ringbell.co.uk/info/hdist.htm

[jomifl]

Bidean nam bian or Ben sgulaird are more likely candidates as although they are lower than Ben nevis they seem to be near enough to be visible

[jomifl]

If Bidean nam bian is less than 120 miles from Benbradagh in the same direction as Ben nevis then it is most likely. Check which side of the paps of Jura it should be as opposed to the othe candiates. I don't have a sufficiently detailed map to hand otherwise I would have a go.

[jomifl]

Ignore most of my first post, I was talking rubbish.

[jomifl]

Ben Cruachan is the right height to be visible at a distance of 120 miles which is how far away it is, it should appear to be a little to the right of the Paps of Jura.

[jomifl]

On second thoughts I was tlking complete sense:-)

[ossian]

If the observer is at a height of 1509 ft and the observed mountain is 4409 ft high this would be the same as observing a mountain 5919 ft high from sea level. This gives an answer of 94.3 miles. Doesn't look like Ben Nevis then. Do you thing that there could be a mirage effect operating?

Many Thanks,

Stewart

[jomifl]

sSewart, you can't just add the heights. The sight line between the 2 peaks just grazes the earths surface at some point in between. It is therefore as if your eye was at the surface at that point and you could see the top of each peak, so you calulate the horizon distance fom each peak and add them together. In this case Ben Cruachan fits the bill. The horizon distance is not directly proportional to height but follows the law explained in the link.

[jomifl]

Apologies for the rubbish typing it is a problem with AB slowing down the typing function so missing letters. I think it is unlikely that a mirage would work on that scale, though it is possible.

[ossian]

Ben Cruachan certainly is the right distance away. The problem with this mountain is that it is not on the direct line from Ben Bradagh and splitting the Paps of Jura. Perhaps my memory is faulty and the distant mountain was a little to the right of the Paps. Will be up there in a few weeks and I will check it out and let you know. Many thanks jomifl for your help and for the web site link.

Stewart

[jomifl]

Stewart, If you can get a compass bearing (assuming it is visible) it may it may help, where is a compass when you need one?