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# Is the Earth flat, or a circle?

Well, first things first a circle is a two-dimensional shape, so a circle is definitely flat.

A sphere is the three-dimensional extension of a circle, so let’s see whether the Earth is flat or a sphere and how we know.

Is the Earth flat? Short answer is no (of course!). But how do we know that? Surprisingly, there are still people who try and argue the Earth is flat, based particularly on things like not being able to see a curved horizon from the shore.

Image credit: Bored Panda.

But this idea assumes that you’d be able to see the curvature across the image – left to right. The problem is that even when we look at the horizon, the size of the Earth means that the curvature is very (very) small. Over 10 km (wider than the view above), the curvature would be less than 10m from one side to the other. You can calculate that for yourself. But if we look straight out at something ‘beyond’ the horizon eg a photo of a ship on a calm sea, around 30 km away in this case. The distant ship lies below the horizon, which only makes sense if the surface is curved. When we look from higher up (20 m above the surface on the right), we can see further over the curvature, so the ship appears slightly higher.

Image credit: Imgur Stack Exchange

Image Credit: Quora.

Read this article from NASA which includes an answer to 'how do we know the earth is round?'.