What is Global Positioning System?
[[File:GPS Receivers.jpg|thumb|right|GPS receivers. People can carry them to detect where they are and plan where and how to go to the next place.]] A '''Global Positioning System''', also known as '''GPS''', is a system of satellites designed to help [[navigate]] on the Earth, in the air, and on water.<ref>{{cite web |author1=Science Reference Section |author1-link=Library of Congress |title=What is a GPS? How does it work? |url=https://www.loc.gov/everyday-mysteries/item/what-is-gps-how-does-it-work/ |website=Everyday Mysteries |publisher=[[Library of Congress]] |access-date=April 12, 2022 |archive-url=https://web.archive.org/web/20220412090940/https://www.loc.gov/everyday-mysteries/item/what-is-gps-how-does-it-work/ |archive-date=April 12, 2022 |date=November 19, 2019 |url-status=live}}</ref> A GPS receiver shows where it is. It may also show how fast it is moving, which direction it is going, how high it is, and maybe how fast it is going up or down. Many GPS receivers have information about places. GPSs for [[automobile]]s have travel data like [[road map]]s, [[hotel]]s, [[restaurant]]s, and service stations. GPSs for boats contain [[nautical chart]]s of [[harbor]]s, [[marina]]s, shallow water, rocks, and [[waterway]]s. Other GPS receivers are made for [[air navigation]], hiking and backpacking, [[bicycle|bicycling]], or many other activities. The majority are in [[smartphone]]s. Most GPS receivers can record where they have been, and help plan a journey. While traveling a planned journey, it predicts the time to the next destination. == How it works == [[File:ConstellationGPS.gif|thumb|GPS satellites circle the earth in four [[Plane (geometry)|planes]], plus a group over the [[equator]]. Blue satellites here are visible to a GPS receiver at 45° North. Red satellites are blocked by the Earth.]] A GPS unit takes radio signals from [[Satellite (artificial)|satellites]] in [[Outer space|space]] in [[orbit]] around the [[Earth]]. There are 31 satellites which are {{convert|20200|km|mi|-2}} above the Earth.