Could someone give any info on the horizon always meeting you at eye level, even on a high mountain or in a plane.
Is there any way to test whether it would meet you at eye level on a globe earth? Or even on a flat earth?
If the earth turned out to be flat, how could you possibly test that horizon theory for a globe earth? And how could you for a flat earth being on a globe?
It's probably simple, but not to me. Sorry.
Yes, I believe it should be quite a good test. Certainly the horizon
appears to rise to meet you eye level. Flat earthers claim everything is due to "perspective", so I surely can claim an equal right!
There will always be questions as to how far the horizon is from us and what is the "dip angle" (as it is called) to the horizon. The variation is largely to due refraction, which can be substantial, but hardly ever more than 0.5°.
There is quite a good paper by
Rohan Academic Computing, San Diego State UniversityDip of the Horizon
When we observe sunset and mirage phenomena, we're usually standing on the surface of the Earth. But standing on the surface doesn't mean our eyes are at the surface. Even at sea, if your eyes were at the surface of the water, your nose would be under it; this isn't a tenable position for very long.
Diagrams in textbooks are often drawn as if the observer is at the surface of the Earth — partly because the height of the eye is very small compared to the size of the Earth: a person's eyes are about 1.6 meters above the ground, but the radius of the Earth is over 6 million meters. But, in this case, “very small” isn't the same as “negligible.” Let's work it out:
This is the Intro, you need to read it.
This dip angle can be calculated, and a few values (based on a typical allowance for refraction):
Eye Height | | Horz dist | | Dip Angle | | Eye Above Horz |
1.5 m | | 5.1 km | | 0.03° | | 3.0 m |
10 m | | 13 km | | 0.09° | | 20.0 m |
100 m | | 41 km | | 0.28° | | 200 m |
1,000 m | | 130 km | | 0.88° | | 2,000 m |
10,000 m | | 412 km | | 2.8° | | 20,000 m |
From even 100 m eye height up a surveyor could easily measure the angle, especially if he could see the ocean on both sides and do a "back sight".
Once you get to a 1,000 m the angle is a trivial measurement for a surveyor, but stretching the accuracy of the levels on smart phones, unless carefully calibrated.
Now, as to why the horizon appears to rise to eyelevel. Take say the case at 100 m elevation, the horizon is about 41 km away any 200 m below eyelevel.
If you drew this out to scale it would look almost horizontal - no time now for a drawing, but "perspective" would make it appear almost horizontal especially without any other reference.
So the horizon certainly appears to rise to eyelevel, till we get to maybe 10,000 m altitude, then some claim to be able see discern it.