How Do We Know Earth is Round?
Members of the Flat Earth Society claim to believe the Earth is flat despite scientists explaining how we know the Earth is round since the third century B.C.
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00:00 How do we know that the Earth is round?
00:05 One of the most famous images of Earth is called the Blue Marble.
00:08 It was snapped in 1972 from a distance of about 18,000 miles by the crew of the Apollo
00:13 17 spacecraft, and it shows our planet as a water and cloud-covered sphere against the
00:18 black backdrop of space.
00:20 However, there are people who claim that this image is part of a vast conspiracy to trick
00:25 people into believing that Earth is round, when in reality, they say, it's as flat as
00:30 a pancake.
00:31 Members of a group known as the Flat Earth Society point to the visible horizon and say
00:35 that since they can't see the curve of the globe, that the planet must be a flattened
00:40 disk.
00:41 How do we know that it's not?
00:43 Well, no one has ever documented this so-called "edge of the Earth," which flat earthers say
00:48 is ringed with a giant wall of ice.
00:51 And scientists have been explaining how we know the Earth is round since the third century
00:55 B.C.
00:56 Earth is so big that from a person's vantage point on the ground, its curvature is simply
01:01 impossible to see.
01:02 But the ancient Greeks were able to "see" Earth's curve by looking at the sun's position
01:07 and comparing shadows that it cast in different places at the same time of day.
01:11 The laws of gravity also explain how a spherical planet would form, with its mass attracting
01:16 matter in space and building a shape outward from a central core.
01:20 And on a spherical planet, gravity's pull from the center is what keeps our feet on
01:24 the ground.
01:25 Not to mention that in the 16th century, Ferdinand Magellan sailed completely around the world,
01:31 which would have been impossible on a flat Earth surrounded by an icy wall.
01:35 Earth isn't a perfect sphere, more like an irregularly shaped ellipsoid, according to
01:40 the National Ocean Service.
01:41 But for those arguing that it's pancake-shaped, that idea falls a little flat.
01:47 The shape of the Earth, just one of life's little mysteries.
01:50 (upbeat music)