Although it’s hard to imagine getting around without a GPS, Galileo Galilei lived in a world without search engines or satellites. His seemingly archaic navigational methods, revolutionary in their time, however, set a powerful precedent for the way in which we find our way around the world today.

Four hundred years later, we’re still building off the concepts Galileo explored. Here are a few key ideas from one of history’s greatest scientific minds that helped pave the way for modern navigation.  

1. We’re not the center of the universe

Heck, we’re not even the center of our own solar system. The notion of a central sun dates back to ancient Greece and was eventually supported by the likes of Copernicus. But it was Galileo who contributed some compelling evidence to support this dangerous idea, and he did it all using his handy homemade telescope. (Yes, he actually built his own telescope!)

By observing the moving spots on the sun’s surface, he determined that the giant star was spinning on its own axis. He also saw the phases and rotation of planet Venus, yet another indicator that Earth was in constant motion, traveling around a central sun.

This discovery opened the door to space exploration, which eventually led to orbiting satellites that make stuff like international phone calls, weekend weather predictions, and your favorite TV show possible.

2. Longitude matters

Galileo tried to calculate longitude based on Jupiter. Well, Jupiter and the revolutions of its various moons, to be exact. Galileo observed these movements through the lens of his telescope, using the speed of the circling moons as hands on a “universal clock” of sorts.

To streamline the calculations of these orbits, especially in relation to a constantly moving earth, he created a measuring tool called a Jovilabe — or for the layperson, a crazy-looking brass thing with 2 little spinning disks, each representing the orbits of Earth and Jupiter.

With these metrics, he attempted to calculate Earth’s longitude while at sea. His experiment, involving a telescope attached to a helmet, was excruciatingly slow and ultimately abandoned. But it did lay the groundwork for other scientists to use this method on land, generating some vastly improved maps of France and parts of North America.

Galileo wasn’t alive to witness these ʺadvanced” maps, and he’d never know how mapping technologies would continue to evolve. Can you imagine his reaction to the interactive, instantaneous, digital maps available on your smartphone? Galileo’s mind = blown.

3. Accuracy is everything

These days we have calculators built into our phones and fancy graphing calculators that do all the complicated stuff. Since nothing like this existed during the Renaissance, there was demand for a device that could perform lots of calculations, particularly in the military.

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Many great minds worked on creating a universal measuring tool during the Renaissance, but it was Galileo who succeeded in 1597 with his variation of the military compass, an adjustable 2-pronged gizmo that could be used for geometry, arithmetic, geographical surveying, and tactical military maneuvers.

The device spawned different variations, until it was eventually replaced by slide rules. Later, the modern electronic equivalents would step in, including the calculator, the personal computer, and — you guessed it — the GPS.  

4. It’s all relative 

You probably think Albert Einstein was the only brain behind this theory, but alas! It actually goes all the way back to Isaac Newton. And the concept was further examined by Galileo in his book Dialogue Concerning the Two Chief World Systems.

In this book, he explained that when a ship’s moving at a constant, unchanging velocity, any given passenger on that ship can’t determine if the ship’s moving or not. It’s a lot like the phenomenon of being on a plane moving hundreds of miles per hour, yet feeling completely still.

It gets more interesting from here. Galileo also outlined that objects behave exactly the same in a moving vessel as they do on land — a bottle dripping water into a tub, one drop at a time, would not be affected by the ship’s movement, as long as that movement is constant. Each drop falls straight down, despite the fact that the ship and everything in it are moving forward.

Paradoxical, is it not? This is the principle of relativity in a nutshell, the concept Galileo used to explain a very peculiar truth, that we all feel still on Earth, a planet that never stops moving.  Earth’s constant rotation, an insane thought in Galileo’s time, is now essential to the space exploration of today.

It’s strange to think that many current technologies have roots in Galilean theory and philosophy. While it’s a shame he couldn’t be around to see how far we’ve come, our core understanding of how the planet functions within our solar system — and of how to get from Point A to Point B on that planet —will always remain part of Galileo’s legacy.

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about Chris

Chris has written everything from fiction manuscripts to pretend newsletters about pirates. He's even edited numerous volumes of work written entirely by kids. As a freelance writer at Esurance, he strives to bring out the whimsy and heart of insurance. Outside of Esurance, Chris is an audiophile, visual artist, and explorer of late-night taquerias.