[Petrochemicals (OP)]

Of course! Light travels faster downhill, so the Irish can see me coming before I see them on the ground. All that wartime stuff about Chain Home Radar was public disinformation: it really was the Royal Observer Corps on a diet of carrots!

I suppose that's how we get tides too.

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I think that this is correct, swingate is a transmitter station with 100m ish tall masts. It does produce a quandary.

This is a shot of Aberystwyth from about 7.5 miles away,

IMG_20230731_083639.jpg (1230 kB . 2301x1447 - viewed 159 times)
It does show the line of sight, the waves are obviously raising the sea level, there is a bit of miraging, but you can see the height of the buildings. The building on the end is the castle and then Aberystwyth University.
0_Old-College-Yr-Hen-Goleg-Aberystwyth.jpg (47.4 kB . 615x409 - viewed 151 times)

[Bored chemist]

That pretty much concurs with the horizon table, particularly at low tide.

Does the table take refraction into account?

[alancalverd]

This is a shot of Aberystwyth from about 7.5 miles away,

Entirely reasonable. Assuming the camera was about  6ft above sea level, you can't see the beach or even the hulls of the inshore yachts. The minimum sum of observer height plus target height at 7.5 miles is about 35 ft.

Does the table take refraction into account?

no. But it's not a lot of help over a long stretch of water: any significant temperature layering is usually accompanied by fog!

[Bored chemist]

You don't need a temperature gradient; gravity is good enough

[alancalverd]

But when we talk about visibility to the horizon from the shore, both the target and the observer are at the same altitude and therefore pretty close to the same pressure and, if we are looking across the sea, the same temperature. At most, you might add 10 - 15% to the visible distance.

[Bored chemist]

But when we talk about visibility to the horizon from the shore, both the target and the observer are at the same altitude and therefore pretty close to the same pressure and, if we are looking across the sea, the same temperature. At most, you might add 10 - 15% to the visible distance.

Do you remember the Daedalus cartoon/ column in Nature and or New Scientist?
Written by David Jones.

He covered the subject. I will see if I can find the book.


But the point is that the change of refraction with altitude is such that light "curves down" and the curvature is nearly the same as the curvature of the earth.

This sometimes upsets flat earthers .

[Bored chemist]

Found it.

IMG_1304.jpg (2372.41 kB . 4032x3024 - viewed 173 times)

[Bored chemist]

And finally

IMG_1306.jpg (2374.58 kB . 4032x3024 - viewed 182 times)

Obviously, the copyright isn't mine.
I'd recommend the book
https://www.amazon.co.uk/Inventions-Daedalus-Compendium-Plausible-Schemes/dp/0716714132

[alancalverd]

the curvature is nearly the same as the curvature of the earth.

So you can establish line of sight communication between any two points with a decent laser. Just as well the Romans didn't know that. Surveyors use an "effective radius" of about  1.17 times the actual radius of the planet to correct their optical height measurements, but clearly they know nothing about surveying.

[Bored chemist]

So you can establish line of sight communication between any two points with a decent laser.

What?
Who said that?

[alancalverd]

If the path of a light beam is curved such that

the curvature is nearly the same as the curvature of the earth.

then a collimated beam will always follow a great circle around the planet, at its initial altitude.

[Bored chemist]

If the path of a light beam is curved such that

the curvature is nearly the same as the curvature of the earth.

then a collimated beam will always follow a great circle around the planet, at its initial altitude.

Tell us you don't know what "nearly" means without saying "I don't  know what 'nearly' means".

If, on the other hand, you made a tunnel 13 km below the earth's surface and let it fill up with air then, yes, you could send a beam of light round the  world.

Whether 13 Km is deep or not depends on perspective.
It about as deep as we have ever drilled.
But compared to the 6300Km radius of the earth, it's pretty near the surface.


Was the problem that you didn't read my post, or that you didn't read the article in the book?

[alancalverd]

OK, how near is nearly? If I fire my laser horizontally from 100 ft above a featureless (no mountains to get in the way) earth-size planet, at what height will it return along some elliptical path? Or if I tilt it down a bit from the top of the only (arbitrary height) mountain, will it get back to me?

[alancalverd]

OK, how near is nearly? If I fire my laser horizontally from 100 ft above a featureless (no mountains to get in the way) earth-size planet, at what height will it return along some elliptical path? Or if I tilt it down a bit from the top of the only (arbitrary height) mountain, will it get back to me?

This does raise some interesting possibilities with respect to small planets with dense atmospheres - like Venus - or all-gas giants .

[Bored chemist]

OK, how near is nearly? If I fire my laser horizontally from 100 ft above a featureless (no mountains to get in the way) earth-size planet, at what height will it return along some elliptical path? Or if I tilt it down a bit from the top of the only (arbitrary height) mountain, will it get back to me?

I don't see any reason to assume that it will be elliptical.
Feel free to do the maths.

[Petrochemicals (OP)]

This is a shot of Aberystwyth from about 7.5 miles away,

Entirely reasonable. Assuming the camera was about  6ft above sea level, you can't see the beach or even the hulls of the inshore yachts. The minimum sum of observer height plus target height at 7.5 miles is about 35 ft.

Does the table take refraction into account?

no. But it's not a lot of help over a long stretch of water: any significant temperature layering is usually accompanied by fog!

It appears on the one hand you can see roughly down to the road which appears about the 10m mark, but the tides can be 7m, the uni building is in orange. The pink boxes display some sort of downward markings as though the image is stretched.

IMG_20230801_221549.jpg (1224.45 kB . 2301x1447 - viewed 157 times)

The sea has waves, but it could be altered in its level by the tidal flow, tides are not equal.

[alancalverd]

I don't see any reason to assume that it will be elliptical.

Because it's "nearly" circular!

[Bored chemist]

I don't see any reason to assume that it will be elliptical.

Because it's "nearly" circular!

If the "force" vs distance function was an inverse square you would get elliptical orbits.
But the bending vs height is not quadratic.
And any other function won't give stable orbits.

[Pseudoscience-is-malarkey]

The British love taking credit for things like this. The mythical King Arthur is a great example of this. No, the Roman Empire was mostly brought down by the "uncivilized" Visigoths who had colonized much of Western Europe, only for themselves to be largely brought down a few centuries later by the soldiers of the new religion (though they were unsuccessful at driving them out of Rome).
There was defiance in the British Illes that at times made things difficult for the Roman occupiers - defiances led by warriors and political figures of sorts who were possibly the influencers of the Matter of Britain. But in the grand scheme of things, the fat statesmen of Imperium Romanum considered them as worrisome as a cloud day.

[alancalverd]

the fat statesmen of Imperium Romanum considered them as worrisome as a cloud day.

And there you have the key to the collapse of all empires. The political core (being composed of parasites) rots, and like any other cancer, it draws resources from the periphery to feed and defend itself, or issues central commands that do not reflect  local intelligence. The distant warriors, farmers and traders who establish, maintain and benefit from an organised society are withdrawn or ignored. Some become rebels, others succumb to depredation from outside, and gradually the Huns, Visigoths, Americans and Scottish Nationalists replace order with chaos, then build a new order remarkably like the old one, until their own internal parasites repeat the process.