After rapper B.o.B.'s Twitter outburst about the Earth being flat, science educators leapt to their feet to let him know where he went wrong. Even Neil DeGrasse Tyson jumped into the fray to help him out, only to find himself sampled in a new song about the Earth's "obvious flatness."

In the aftermath, the BBC and Popular Science both gave great quick summaries about how we know that the Earth is round, presumably shaking their heads in sorrow the entire time.

Ultimately, though, Flat Earthers are most convinced by one thing: their own eyes. In their minds, when they look at the Earth, they see a flat surface. Why believe a bunch of scientists instead of trusting your own eyes? The answer, of course, is that we are too close to Earth to see that curvature. If you don't believe me, look at a gosh darn coin.

Now, let's close in on its edge, where it is undoubtedly round.

Now let's blow that up and get a little closer.
And closer.
And closer.
Keep going ...
Starting to notice anything? Let's blow it up again.
One last time.
Well, what do you know? We end up with something that looks a whole lot like a flat line. Of course, it's a bit blurry and pixelated since we're using an image instead of a microscope, but the principle is the same: the closer you get to a curve and the more gradual that curve is, the more it appears straight. It took us only seven closeups, reducing the original image to about one-twelfth of its original size to make it look pretty darn straight.
Meanwhile, the human field of vision, for a six-foot-tall person looking out to the horizon, is about three miles. That's one-8,300th of the total circumference of Earth.
And that's how you use a dollar to prove to your Flat Earther friends that you're right.
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