This Is How We Know Earth Isn’t Flat

Hey there! Welcome to Life Noggin. Right now you’re probably watching this
video from somewhere on Earth… that big, round planet you humans call home. But how do you know the Earth is round? Your senses would tell you that it’s flat. After all, if you stand in a large field,
it actually looks pretty flat. And if you walk through that field, it doesn’t
feel like you’re going over a curve. Could it be that the Earth is actually flat? Let’s try an experiment. Say you’re standing in a field outside of
Chicago. If the Earth is flat, you should be able to
look southwest and see some of the tallest points in the United States, the Rocky Mountains. But you can’t. That’s because of the curvature of the Earth. You’ll notice a similar problem if you stand
on a seashore and try to watch a boat sail away. After awhile, it will disappear from view. And not only that, but the bottom part of
the boat will vanish before the top as it goes over what’s called the horizon line
— the place where the sky meets the Earth. For someone who is six feet tall, the horizon
line is only three miles away. But the higher up you are, the farther you
can see over the Earth’s curve. This is why standing on a tall mountain might
allow you to see over 100 miles while standing in a field will only let you see a short distance. It also means that taller people can see slightly
farther than shorter people. Good thing my animator can make me any height! The thing is, none of this is new information. We’ve known about the planet’s curvature
for over 2000 years. The Ancient Greeks figured out that the Earth
is round based on several pieces of evidence, including their observations of ships going
over the horizon line.The scientist Aristotle, writing in 350 BCE, noted that during an eclipse,
the Earth makes a round shadow on the moon. He also realized that stars appear in different
places depending on where you are standing. For example, he saw stars in Egypt that weren’t
visible farther north. Roughly 100 years later, humans got their
first measurements of the Earth’s curve from another Greek mathematician, Eratosthenes. He had heard of a city in southern Egypt where,
at noon on the summer solstice, the sun was directly overhead and the buildings cast no
shadows. But at the same time in the northern city
of Alexandria, the buildings DID cast shadows… meaning the sun was at a different angle in
the sky. On the day of the solstice, Eratosthenes stuck
a stick in the ground in Alexandria and measured the angle of its shadow. Using the distance between the two cities,
he was able to calculate the curvature of the Earth! You could perform this same experiment if
you have a friend living a few miles away. Or, if your friend is several hours west,
you can get more proof that the Earth is round by calling them at sunset and asking how the
sky looks. It will still be daylight there because of
the Earth’s curve. And there’s one more piece of clear evidence
for the planet’s shape — pictures taken from space. Maybe you’re not on Earth after all and
are actually watching this video from the space station… in which case, please leave
a comment, because that’s cool. If that’s true, you’ll have a bird’s-eye
view of this giant blue and green globe. What a beautiful place to live. Do you love science? Do you love video games? If so, you HAVE to check out Play Noggin. Julian recently explored the idea of mind
control. Check it out! What other myths about Earth do you want me
to explore? Let me know in the comment section below.

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