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Visibility

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 wintertree 10 Jul 2022

There’s been stunning conditions for long range visibility over the last couple of days.  Today we saw the Cheviot from Captain Cook’s monument in the North York Moors; I wish I’d had a better camera than my phone on me.  I reckon it’s 80 miles as the crow files.  Walking west from the monument the air smelt of bilberries, I’ve never known a day like it.

What other long distance sightings have people had?  This was from pretty low down so I imagine it’s been phenomenal from the top of the Cumbrian fells.


 Chris Craggs Global Crag Moderator  UKC Supporter 10 Jul 2022
In reply to wintertree:

I noticed the same yesterday up on Stanage, I could make out the North York Moors which has to be 70+ miles away,

Chris

 Graeme G 10 Jul 2022
In reply to wintertree:

> What other long distance sightings have people had?

I saw the Moon last night.

I’ll get my coat…….

 tjdodd 10 Jul 2022
In reply to Graeme G:

> I saw the Moon last night.

> I’ll get my coat…….

Pah, I saw the Sun today.

 crayefish 10 Jul 2022
In reply to wintertree:

On a reeeeaally clear day from a local hill in Tarn-et-Garonne (France, where my parents live), one can just make out the Pyrenees one way, and the Massif Central the other way.  A rare but amazing sight.

 streapadair 10 Jul 2022
In reply to wintertree:

On An Caisteal, extreme left of the skyline are Ben More and a'Chioch on Mull. Only 52 miles or so, but this was by moonlight.


 Dave Hewitt 10 Jul 2022
In reply to wintertree:

> There’s been stunning conditions for long range visibility over the last couple of days.  Today we saw the Cheviot from Captain Cook’s monument in the North York Moors; I wish I’d had a better camera than my phone on me.  I reckon it’s 80 miles as the crow files.  Walking west from the monument the air smelt of bilberries, I’ve never known a day like it.

The Cheviot was also easily in view form Ben Cleuch in the Ochils about midday today - 80 miles according to both the summit indicator (the Cheviot is the furthest-away hill on it) and Jonathan de Ferranti's excellent Viewfinder Panoramas - here's the reverse version from the Cheviot:
http://www.viewfinderpanoramas.org/panoramas/ENG/CHEVIOT.GIF

The Cleuch-Cheviot view isn't that unusual - I see it maybe five or six times most years - but today was a very clear version of it. Plus it was pretty warm, especially low down.

(Great An Caisteal picture, streapadair.)

 Fat Bumbly2 10 Jul 2022
In reply to Dave Hewitt:

Saw Ben Cruachan from our holiday cottage for the first time in over a week.  I can confirm that Ardgour hills do have tops after today.

In reply to Graeme G:

> I saw the Moon last night.

Keeping it astronomical, I saw Uranus...

2
OP wintertree 11 Jul 2022
In reply to Dave Hewitt:

> The Cleuch-Cheviot view isn't that unusual - I see it maybe five or six times most years - but today was a very clear version of it. Plus it was pretty warm, especially low down.

Yes, I also thought it was a very clear view; I wondered if anyone had achieved the Merrick-to-Snowdon sight line over recent days?  It's been reported before - https://www.ukclimbing.com/forums/hill_talk/has_anyone_really_seen_southern_scotland_from_snowdon-494707 - but cold conditions were cited, not this level of heat.

In reply to Graeme G:

> I saw the moon last night

It's crazy how thin the atmosphere on the planet is - less than 10 km of sea-level equivalent air in the path to the moon once it gets away from the atmosphere.  

in reply to streapadair:

That's fantastic.  If this was a competition, moonlit shots would get their own category.

In reply to wintertree:

Why is it so clear currently? I drove out to go climbing at Stoney Middleton on Friday evening, and as I take the road out of Dronfield just before Owler Bar (for Sheff/Chesterfield people) there is a great view down over Sheffield to the NE and Chesterfield to the SE. But it was very very clear looking over the towns and much further away. Some windfarms and cooling towers which you can often see looked like they were so much closer than normal just because of the clarity. I normally think of clear air being after rain, and often colder conditions. But this was after a period of dry and warm weather, with very high pollen counts that you would think suggests there is lots of muck in the air?

OP wintertree 11 Jul 2022
In reply to TobyA:

>  But this was after a period of dry and warm weather, with very high pollen counts that you would think suggests there is lots of muck in the air?

Pollen probably isn't a good indicator because it's source is so season and weather dependant.  The "pollution" score on the BBC weather page for us is showing L for low which might be a better general indicator. 

Why conditions are so good now is a fascinating question and I'm hoping someone on here knows more.   Atmospheric conditions seem very unusual at the moment - planes have been leaving dashed-line contrails as they presumably go through atmospheric waves of some sort, clouds are forming very "blown out" shapes, and heat haze is much lower than I'd have naively expect.  The best I get on my occasional commute the I did today was a 40-mile view, but again it was exceptionally clear. 

Two different things seem to have aligned - good "seeing" and low particulate/droplet scattering.  I don't know how much of the normal limits to visibility come from particulates (pollution, pollen, sub-saharan dust etc) vs droplets (water).

"Seeing" is what astronomers call the distorting effect of temperature differences in the air bending light erratically and blurring out detail, and hot weather is normally an obvious cause of very bad horizontal seeing.  Which is why I was so surprised at recent conditions; perhaps it suggests that somehow the heating of the atmosphere is unusually homogeneous.  Relative humidity and wind conditions don't seem unusual.  There is a distinct lack of cumulonimbus formation on an evening, which is something I'd normally be looking for after such weather.  Optical turbulence and seeing is not unrelated to ground layer turbulence experienced by aircraft - I wonder if it's all smooth landings right now?

 Enty 11 Jul 2022
In reply to wintertree:

The Barre des Ecrins from the Pyrenees. 443km.

https://beyondrange.files.wordpress.com/2016/08/bp1410102-mbret1.jpg

E

OP wintertree 11 Jul 2022
In reply to Enty:

You win.

I reckon yesterday's conditions would have given 300 mile visibility in Britain if we'd had some alps to play with.  There can't be many views as long as yours where the curvature of the planet doesn't limit them.

In reply to Enty:

There's an even longer potential sightline than that.

https://calgaryvisioncentre.com/news/2017/6/23/tdgft1bsbdlm8496ov7tn73kr0ci1q

 Enty 11 Jul 2022
In reply to wintertree:

It wasn't me who took it wish it was. 

Although last week you could see Monte Viso from The Ventoux which is about 155km.

A friend of mine has a place in the hills above Cannes and he always sends me a photo of the mountains in Corsica at sunset. (200km)

E

Post edited at 13:07
 Marek 11 Jul 2022
In reply to wintertree:

I believe another major component of 'seeing' is the velocity of the jetstream. Too low is bad, but too high (>20m/s) is even worse. Related to turbulence at shear boundaries, perhaps.

OP wintertree 11 Jul 2022
In reply to Marek:

> I believe another major component of 'seeing' is the velocity of the jetstream. Too low is bad, but too high (>20m/s) is even worse. Related to turbulence at shear boundaries, perhaps.

In astronomical seeing, yes.  There, the location of optical turbulence typically breaks down in to boundary layers - the ground layer, the jet stream and between 0 and perhaps up to 8 other layers, each with different wind velocities and located between the ground layer and the jet stream.  As you say, shear boundaries between the different wind velocities are a driving force.

For two mountain peaks below 1 km, almost all of the sight-line is above the ground layer and perhaps below the first night-time boundary layer.  I'm not up to date on the structure of daytime seeing but it's coming back in to fashion with solar astronomers and people who study tanks from a long way away horizontally.

Edit: Reading around, it seems the relatively low relative humidity this week is part of the secret sauce for the visibility.  

Post edited at 14:48
 MikeR 11 Jul 2022
In reply to TobyA:

I think it's largely due to where the air currently over us has originated from. Often with these sort of temperatures the air has come from continental Europe, typically France or Spain, where it picks up lots of pollutants. These often get trapped under a temperature inversion, giving us hazy visibility. 

The high pressure system over us has originated from the Azores, so has picked up  very little pollutants on route to us, hence the clear air.

 Marek 11 Jul 2022
In reply to wintertree:

The other thing that comes to mind is that if you get low wind and strong sunlight heating the ground (relative to air temperature) you'll get lots of small convection cells between you and the target which will cause blurring. Just a guess as to whether that's significant.

OP wintertree 11 Jul 2022
In reply to MikeR:

I'd forgotten about the particulates maps on Nullschool [1] - PM10 looks very low over Northern England at the moment (you have to hover over the colour scale to read the levels off and it's a log scale, so blue is much lower than red)

[1] https://earth.nullschool.net/#current/particulates/surface/level/overlay=pm10/orthographic=-357.59,51.25,731

In reply to tjdodd:

> Pah, I saw the Sun today.

Amateur. I saw some stars last night and they were a lot further away than the sun or anything else in our solar system.

 inboard 29 Jul 2022
In reply to wintertree:

Yesterday, sailing S down Inner Sound from Torridon to Kyle of Lochalsh, we were seeing objects 80NM distant in Outer Hebrides chain. Also some fantastic, strong refraction artefacts from a longer distance than usual (IME) off Scotland. I think due to cool air. 
 

last year (late July) was on Heaval (381m), Barra, and could see St Kilda, Skye, Morar hills, Mull, and Paps of Jura and a hint of Islay - reckoned visibility was at least 90NM. Amazing day. 

In reply to Graeme G:

> I saw the Moon last night.

> I’ll get my coat…….

Well it is cold on the Moon

 Holdtickler 30 Jul 2022
In reply to wintertree:

On a really clear day, from the hills above Lancaster you can see the Isle of Mann and sometimes even Snowdonia. Having also seen the Lakes and Mann from Snowdon/Yr Wyddfa and having seen Wales, the Lakes and Ireland from Mann I feel really quite triangulated

 Dave Hewitt 30 Jul 2022
In reply to inboard:

> Yesterday, sailing S down Inner Sound from Torridon to Kyle of Lochalsh, we were seeing objects 80NM distant in Outer Hebrides chain. Also some fantastic, strong refraction artefacts from a longer distance than usual (IME) off Scotland. I think due to cool air. 

Sounds good. It was also very clear the day before that, Wednesday - I was on Beinn Dorain with friends and we could pick out all manner of stuff, including the big Galloway hills at 90-odd miles (although it was hard to ID individual summits there as they tend to merge). Tinto at 75 miles was remarkably clear and sharp, and the northern view was good too, eg we could easily see the Strathfarrar ridge through the Grey Corries gap. Lots of islands in view including Colonsay at a mere 65 miles but handily in the Scarba/Cruachan gap. It was high grey cloud rather than proper sunshine, and that seemed to sharpen things nicely with no haze.

http://viewfinderpanoramas.org/panoramas/GRW/DORAIN.GIF

 Matt Podd 30 Jul 2022
In reply to wintertree:

One cold snowy weekend many years ago, on Saturday I went up the Glyders and saw Ireland and Pembrokeshire. On Sunday I went up the Carneddi and could see the Isle of Man, The Lake district hills and the hills of Galloway. I was impressed!

In reply to wintertree:

I once saw the top of the Snowdon Horseshoe poking over the top of distant hills, from the top of Harborough or Reinstor rocks, 95 miles to the east. The profile was very distinct - similar to the view from Cerrigydrudion - but right on the limit of visibility. I took a compass bearing - it was more or less due west of Harborough, so at first I scarcely believed it, because I thought Snowdonia was more north of west than that. But I confirmed the westerly bearing with an atlas when I got home.. This was the only time I saw Snowdon in six years of visiting Harborough very regularly (I lived nearby), even though there were many days when the visibility seemed very good - so there must have been some special atmospherics on that particular day.

1
 Billhook 30 Jul 2022
In reply to wintertree:

Wow, I've lived next to the NYMNP for donkey's years, and i'e never even tried, or thought of looking north in terms of what hills I can see from on't moors.  I bet a nice high pressure during winter would also be an ideal time to look.

 Marek 30 Jul 2022
In reply to John Stainforth:

Pah, half a job. Come back when you've seen Harborough Rocks from the top of Snowdon. Then you'll get the full tick.

It begs the question: What are the two most separated points on the earth surface that could be mutually visible give clear enough air?

 Dave Hewitt 30 Jul 2022
In reply to wintertree:

Has anyone here ever seen the alleged view of (a) Lincoln Cathedral and/or (b) the Humber Bridge from Crich Stand? I was brought up within walking distance of Crich and was there lots as a youth and continued to go there from time to time when visiting my late parents. I've never had a view of said structures either from the trig or the tower itself, despite having been up there on some pretty clear days and with bearings and binoculars in use. Various cooling towers down on the Trent/Soar have always tended to be the limit.

In reply to Marek:

> Pah, half a job. Come back when you've seen Harborough Rocks from the top of Snowdon. Then you'll get the full tick.

> It begs the question: What are the two most separated points on the earth surface that could be mutually visible give clear enough air?

Incidentally, I did get in a F16 fighter on google Earth, and flew straight west from Harborough to Snowdonia (in about ten minutes), did a massive banking turn round the Snowden massif and flew straight back to Harborough. Does that count?

(From Wikipedia): The three longest "sight lines" on Earth are over 300, 400 and 500 km, respectively. Depends quite a lot, of course, on the altitude of the two places.

In reply to Dave Hewitt:

I am pretty sure I have seen Lincoln Cathedral from Crich Stand. It's less than 50 miles away.

 pec 30 Jul 2022
In reply to wintertree:

A couple of years ago I was on Merrick in the Southern Uplands and could make out Snowdon.

When I got home I checked up on it and it turns out this is the longest sightline in the UK at 144miles.

Funnily enough however, for all practical purposes, you can't see Merrick from Snowdon due to the keyhole effect of mountains close to Merrick. By that I mean Merrick might be in your field of vision from Snowdon you you can't identify it. It's explained here:

http://www.viewfinderpanoramas.org/panoramas.html#longlinesbrit

 Dave Hewitt 30 Jul 2022
In reply to John Stainforth:

> I am pretty sure I have seen Lincoln Cathedral from Crich Stand. It's less than 50 miles away.

Thanks - it's good to know at least someone has seen it! Jonathan de F has a Viewfinder thing for Crich and he reckons it's only 41 miles to Lincoln:

http://viewfinderpanoramas.org/panoramas/ENG/CRICH.gif

which as you say means it's not particularly far. General industrial haze/murk seems to be more of a factor there than up here (Stirling), however. Not sure how many times I've been to the Stand - maybe 30, of which perhaps half a dozen have felt clear enough to be able to see Lincoln, so maybe I've just been unlucky. I'm very fond of Crich Stand, largely due to childhood memories but also because it's a strong candidate for "last hill in the Pennines"; the Chevin also gets mentioned but Crich always feels like a more proper hill than the Chevin (even though I have walked through Milford Tunnel).

In reply to wintertree:

Could see Buckden Pike and Great Whernside from Holme Moss yesterday.

 Marek 30 Jul 2022
In reply to John Stainforth:

> (From Wikipedia): The three longest "sight lines" on Earth are over 300, 400 and 500 km, respectively...

Well that sent me down an internet rabbit-hole!

In reply to Dave Hewitt:

That http://viewfinderpanoramas.org site is a goldmine.

Post edited at 11:41
 Dave Hewitt 31 Jul 2022
In reply to pancakeandchips:

> That http://viewfinderpanoramas.org site is a goldmine.

Indeed, it's been around for years and seems pretty accurate. New stuff keeps getting added, always interesting. I mainly use it for post-hill checking but I also have a few of the laminated printed versions, useful on site as it were. Jonathan who runs it is a good bloke, and the site is a proper labour of love. It's one of my favourite hill things.

Incidentally, re long views (and impossible ones), I once asked another friend, Grant Hutchison, who is able to work out these things and seems to enjoy doing the maths, how far from intervisibility Ben Lomond and Skiddaw were, given that they're effectively adjacent 3000ft hills - most southerly Scottish, most northerly English. Grant did a few sums and reckoned that in normal good visibility (with only slight refraction), both hills would need to be a couple of hundred metres higher to be seen from each other. This surprised me - I'd thought it would be less than that, partly because I've always been struck by how soon down the M74 Skiddaw appears - it's directly ahead on that long straight stretch near Lockerbie - and also because of the extraordinary view of the Lakes you can get from Tinto, which is almost a Central Belt hill and only 700-odd metres high. Take a look at this, on Jonathan de F's site - he reckons you can see Pillar (77 miles) and Wetherlam (86 miles) from Tinto.

http://viewfinderpanoramas.org/panoramas/UPL/TINTO.GIF

Both these I find astonishing, and would love to see - particularly Wetherlam, given that I've spent masses of time in Coniston. Next time I'm in Coniston on a really clear day I'll go up Wetherlam and look for Tinto.

PS - Fat Bumbly2 on here has seen St Kilda from Sgurr nan Gillean on Skye, which must have been quite something. I've seen Kilda from Beinn Edra on the Trotternish ridge, clear enough with the naked eye to pick out both distinct parts.

In reply to Dave Hewitt:

I wonder how many photographers there are chasing the clear conditions to collect long sightline shots? That sounds like a good hobby for when I get a bit older...


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