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Here’s how we know the Earth is round

posted by Jason Kottke   May 23, 2017

Flat-Earthers aside, people have known that the Earth is round since at least the 3rd century BC. This quick video explores a few of the ways we know the world is spherical, some of them quite simple to recreate as experiments. See also Top 10 Ways to Know the Earth is Not Flat.

(5) Seeing Farther from Higher

Standing in a flat plateau, you look ahead of you towards the horizon. You strain your eyes, then take out your favorite binoculars and stare through them, as far as your eyes (with the help of the binocular lenses) can see.

Then, you climb up the closest tree — the higher the better, just be careful not to drop those binoculars and break their lenses. You then look again, strain your eyes, stare through the binoculars out to the horizon.

The higher up you are the farther you will see. Usually, we tend to relate this to Earthly obstacles, like the fact we have houses or other trees obstructing our vision on the ground, and climbing upwards we have a clear view, but that’s not the true reason. Even if you would have a completely clear plateau with no obstacles between you and the horizon, you would see much farther from greater height than you would on the ground.

This phenomena is caused by the curvature of the Earth as well, and would not happen if the Earth was flat.

Update: Carl Sagan explains how Greek astronomer and mathematician Eratosthenes figured out how the Earth was round in ~200 BC.

(via @preshit)