NASA | Looking Down a Well: A Brief History of Geodesy


Uploaded by NASAexplorer on 23.02.2012

Transcript:
[music] Narrator: 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 analyzing 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.
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