Looking Down a Well: A Brief History of Geodesy скачать в хорошем качестве

Looking Down a Well: A Brief History of Geodesy

Geodesy is a field of study that deals with the measurement and representation of the Earth, and it all started when a clever human named Eratosthenes discovered that you could measure the circumference of the Earth by looking down a well. Over time, the field of geodesy has expanded and evolved dramatically, and NASA uses technology like radio telescopes, ground surveys, and satellites to contribute! Learn more about geodesy in this video! TRANSCRIPT: A long time ago, in Ancient Egypt, a clever human named Eratosthenes figured out that when the Sun was directly above a deep well in one city, you could stand in a nearby city to the north, measure the angle of the shadows there, and multiply that by the distance between the two cities to get the distance around the entire Earth. With that, the science of geodesy was born. Geodesy deals with the measurement and representation of the Earth--or, to put it more simply, it's the science of where things are--and just as importantly, where they have been, and where they are going. Through geodesy, we learned the rough size and shape of the Earth, the direction of its rotation, its distance from the Sun, and more. Through triangulation, we could create detailed maps of entire countries. We even figured out that the Earth isn't quite a perfect sphere, and after some arguments and expeditions to Lapland and Peru, we measured that it's just a bit thicker in the middle. Building on this information, we found tons of practical uses for geodesy. Using stars as reference points and accurate watches, we could reliably determine latitude and longitude so that ships could cross giant oceans to get where they needed to go. Explorers visited uncharted regions, mapped them, and even found the tallest mountain in the world. Later, engineers built railroads to get us to all of these places. With a little math and the same reference surface, rail tunnels could be started on both sides of a mountain and somehow still meet in the middle. Life was good. And once we invented radio telescopes and satellites, things got even better. When scientists used a bunch of small radio dishes like one big one to look at quasars, somebody got the idea that you could use these measurements to determine very accurately the distance between the telescopes. Now, we can look at the movement of the Earth's crust, changes in how long days are, and how the Earth wobbles on its axis. Satellites also became very important. By analyizing their orbits, we can learn about our planet's changing size and shape and gravity, and by making laser measurements, we can look at everything from changes in the height and shape of the oceans and ice sheets, to how the tides work. So, from ancient Egypt to the hundreds of satellites in orbit today, geodesy continues to have a huge impact on our lives. And all because somebody, a long time ago, decided to look down a well.