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[music] Narrator: A long time ago, in ancient Egypt,

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a clever human named Eratosthenes figured out that when the Sun was directly above a deep

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well in one city, you could stand in a nearby city to the north, measure the angle

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of the shadows there, and multiply that by the distance between the two cities

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to get the distance around the entire Earth. With that, the science of

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geodesy was born. Geodesy deals with the measurement and representation

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of the Earth--or, to put it more simply, it's the science of where things are, and just

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as importantly, where they have been and where they are going. Through geodesy,

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we learned the rough size and shape of the Earth, the direction of its rotation,

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its distance from the Sun, and more. Through triangulation,

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we could create detailed maps of entire countries. We even figured out

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that the Earth isn't quite a perfect sphere, and after some arguments and expeditions

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to Lapland and Peru, we measured that it's just a bit thicker in the middle.

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Building on this information, we found tons of practical uses for geodesy.

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Using stars as reference points and accurate watches, we could reliably

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determine latitude and longitude so that ships could cross giant oceans to get

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where they needed to go. Explorers visited uncharted regions, mapped them,

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and even found the tallest mountain in the world. Later, engineers built railroads

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to get us to all of these places. With a little math and the same reference

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surface, rail tunnels could be started on both sides of a mountain and somehow still

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meet in the middle. Life was good. And once we invented radio

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telescopes and satellites, things got even better. When scientists

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used a bunch of small radio dishes like one big one to look at quasars, somebody

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got the idea that you could use these measurements to determine very accurately the

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distance between the telescopes. Now, we can look at the movement of the Earth's crust, changes

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in how long days are, and how the Earth wobbles on its axis. Satellites

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also became very important. By analyzing their orbits, we can

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learn about our planet's changing size and shape and gravity, and by making

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laser measurements, we can look at everything from changes in the height and shape of the oceans

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and ice sheets to how the tides work. So, from ancient Egypt to

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the hundreds of satellites in orbit today, geodesy continues to have a huge

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impact on our lives. And all because somebody, a long time ago,

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decided to look down a well.