The photo I uploaded to the gallery, http://www.weather-watch.com/gallery/displayimage.php?album=4&pos=1, shows the view of France from our roof window late this afternoon looking SE from Broadstairs. It must be at least 25 miles or more away, Dover is the nearest to France (Calais) at some 22 miles and we are 18 miles NNE of Dover. We can often see the coast of France but it is not usually as clear as this. It was taken with a 450mm lens, but to the naked eye was actually clearer.
Can anyone explain the atmospherics which allow this to happen?
Hi
i thought this was caused by water vapour acting as a magnifying glass but i could be wrong
i do know that if conditions are right you can see the gas Riggs on the Morecambe gas field in Morecambe bay from the business park i work from just outside Douglas, also can see Sellafield in Cumbria from Maughold in the north of the island
Harold
I can understand ranges, if by that you mean high hills and mountains. I’m talking here about the French coast and none of it is much higher than we are here in Broadstairs, maybe 100-150 feet ASL. This effect of seeing France is visible on the beach actually at sea level. Now I understand the horizon ASL is no where near 25miles. The horizon is about 5 kilometers for the average person and from my house (being up on a hill a little behind the actual cost) it will be some where between 20 and 22 kilometers which is much less than the width of the English Channel!
ah, OK, i understand now
a similar thing happens in the mediteranean, where a certain port town can be seen up in the sky above the horizon, and is in folklore etc
i read about it just the other day
i think it was like a mirage effect…
a layer of warm air on the sea surface refracting the light and bending it…something like that
looming is what is happening by the looks:
LOOMING: The appearance above the horizon of a distant object that would normally be hidden below it. This effect is caused by unusually large terrestrial refraction, usually due to a thermal inversion. Looming is the opposite of sinking. Both are refraction phenomena, but not mirages. (See the table of refraction phenomena.)
Thanks Brian I knew there must be a technical explanation of it. Strange that the actual word looming is not an uncommon word. Anyway I now know what it is. It was extremely clear yesterday which is why I tried to photograph it, it is not uncommon to see France but there was so much detail it looked really strange!
If, in fact, you are 150’ asl, you will be able to see any object 25 statute miles away if it is higher than 40’ without any refraction. If the French cliffs are also 150’ high, you will see 110’ of them. Note that this is calculated on the geometric horizon, not the optical horizon which is always slightly more favourable towards viewing distant objects, not because of temperature inversions but simply because air is normally denser at low altitudes than at higher altitudes, causing minute changes of refractive index.
Don’t forget that the horizon is only half way to the most distant object of the same height that you could see (if it’s large enough).
Here’s a little calculator to do the sums…http://homepages.nildram.co.uk/~vwlowen/java/horizon.htm Radio and optical lines of sight can be taken as approximately the same most of the time (although both light and radio signals can do strange things in some cases!)
I simply dont believe you can normally see objects at 25 miles distant from here. In fact I know that on a very clear day we cannot see France, we do often get this ‘looming’ effect and can see the French coast but it was unusually clear yesterday and was visible from the beach which without getting your feet wet is as near sea level as you are going to get!
The horizon in the sea/sky interface. If your eyes were good enough and you had a friend of the same height who could walk on water, if he stood in a spot 10km from you and waved a flag above his head, you would see the flag over the horizon. For equal heights, the line of sight is twice the distance to the horizon.
However, that doesn’t explain how you could see 40 miles when standing at sea level, so the other effects mentioned here were almost certainly having an effect. If the picture from your house was over the same path then line of sight still wouldn’t account for it…you could see 150ft cliffs up to about 50km away from your house. You originally guessed at something like 25miles (40m), so line of sight would be possible over that distance.
