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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!
Quote from: alancalverd on 28/07/2023 11:27:02That pretty much concurs with the horizon table, particularly at low tide.Does the table take refraction into account?
That pretty much concurs with the horizon table, particularly at low tide.
This is a shot of Aberystwyth from about 7.5 miles away,
Does the table take refraction into account?
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.
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.
If the path of a light beam is curved such that Quote from: Bored chemist on 31/07/2023 17:33:24the 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.
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?
Quote from: Petrochemicals on 31/07/2023 08:38:03This 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.Quote from: Bored chemist on 28/07/2023 13:30:22Does 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!
I don't see any reason to assume that it will be elliptical.
Quote from: Bored chemist on 01/08/2023 18:09:29I don't see any reason to assume that it will be elliptical.Because it's "nearly" circular!
the fat statesmen of Imperium Romanum considered them as worrisome as a cloud day.