Nothing could be further from the truth and this really exposes just how little Flat Earthers understand about the geometry of what they see.@ColdDimSum @king_of_bob @EngineerMikey99 @UnCastellsMes @vegnoggin @TakeThatDarwin @valtolhurst @alankirton @TakeThatCaps The Mediterranean is 2400 miles long. Using this fake curve, the circumference of earth is wrong. pic.twitter.com/4b16pvDOQy— emanuel (@emanuel14486948) April 9, 2017

Here is a computed view of the horizon from 400km up -- roughly where the ISS orbits the Earth.

So what exactly is that boundary between Earth and Sky we see in the distance?

How about this Spheroid?

The closer we get, the less of the sphere we can see... but we ALWAYS have a horizon and even at 400km above Earth that horizon is a FRACTION of the whole Earth.

So what is the horizon?

First of all, the HORIZON is the visible boundary between our spheroid and whatever lies beyond. It literally comes from "Limiting Circle". And it says nothing about the shape of whatever is INSIDE that circle -- but the horizon itself is a circle. If you are out on the ocean the horizon is about equidistant in every direction around you. That's called a circle. How do Flat Earthers fail to understand this?

THE HORIZON IS A CIRCLE.

And, more importantly, it is a CIRCLE that is perpendicular to the sphere -- it is NOT the EDGE of the sphere which would be Earth sized. You can never see such a thing. At a very great distance it APPEARS that you are seeing "The Sphere" but you aren't, you are seeing up to the limit of your horizon on that sphere -- which approaches seeing 1/2 of the sphere.

But as we get further away we're seeing that last bit of the sphere at an increasingly sharp angle -- and with Earth's atmosphere, that means that you really cannot make out anything for a substantial portion of the distance which you can *theoretically* see. A huge portion of that distance makes up a tiny little sliver of your visual field -- too small for your eyes to resolve usually, and too distant and blurry for even a telescope to do much good at greater distances.

In short -- the horizon is the GREEN line in this diagram. And, as shown, this is a little more than TWICE the altitude of the ISS.

The grid above is not just an arbitrary grid either - I created it to fit an image taken from the ISS.

And, as you can see, it fit rather nicely:

And then I also compared that with a Google Earth computed view using Google Earth Pro image overlay -- since images don't capture the exact lat/long/heading/angles it take a little work to get some arbitrary image to line up but the fit here is pretty good. Showing that the DISTANCES here are exactly as they should be. And once you understand that the horizon is a circle centered at your feet and ALMOST parallel to your eyes as you look out towards the horizon it's easy to understand why that arc SHOULD NOT and COULD NOT form an Earth sized circle... it's not a CIRCLE at all from your viewpoint, it's an ellipse -- which is a circle viewed at an angle.

Circles viewed at an angle are ellipses.

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