The central idea of the passage is that GPS (Global Positioning System) utilizes a network of satellites, ground stations, and receivers to accurately determine a person's location anywhere on Earth, similar to how ancient navigators used the stars for guidance.
Which sentence best states the central idea of the passage?
How GPS Works
adapted from NASA
Humans have looked to the skies to find their way since ancient times. Ancient sailors used the constellations in the night sky to figure out where they were and where they were going.
Today, all we need is a simple hand-held GPS (short for Global Positioning System) receiver to figure out exactly where we are anywhere in the world.But we still need objects high in the sky to figure out where we are and how we get to other places.
Instead of stars, we use satellites. Over 30 navigation satellites are zipping around high above Earth. These satellites, along with the network that supports them, can tell us exactly where we are.
GPS is a system. It's made up of three parts: satellites, ground stations, and receivers.
Satellites act like the stars in constellations—we know where they are supposed to be at any given time.
The ground stations use radar to make sure they are actually where we think they are.
A receiver, like you might find in your phone or in your parents' car, is constantly listening for a signal from these satellites.The receiver figures out how far away it is from some of the satellites.
Once the receiver calculates its distance from four or more satellites, it knows exactly where you are. Presto! From miles up in space, your location on the ground can be determined with incredible precision!
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