Where on Earth? A Look at GPS

Click on the GPS receiver to see what each button is for. Photo OM

Stars and Navigation
Imagine waking up in the middle of nowhere, all alone. How would you know where you were? On a clear night, you could look up at the stars. If you could measure precisely what angle various stars were from you at precise hours, you could calculate your position. That is what sailors did for many centuries, using a special tool called a sextant.

Many birds that migrate at nighttime use the stars for navigation, too. They simply migrate toward or away from the North Star.

GPS: Navigating Made Easier
The problem with depending on the stars to set a direction or find out where you are is that stars are only visible at night, and only when clouds don't cover them. That's why the Global Positioning System (GPS) was started. Instead of stars, this system uses satellites—"human-made stars." GPS is a worldwide radio-navigation system based on 24 satellites and their five ground stations. Each of the satellites sends out a unique radio signal.

A GPS receiver (click the photo to enlarge) works like a radio, but it gets its signals from the satellites instead of from radio stations. As long as a GPS receiver can get signals from at least three or four satellites, it can calculate precisely where on Earth it is. The calculations are based on the time it takes for signals from the satellites to reach the receiver. GPS can be used to figure out where you are on the planet—any time of day, in any weather.

Hear ultralight pilot Joe Duff tell how GPS helps
Photo Operation Migration

Moving Right Along: GPS Helps!
A GPS receiver can do more than calculate where it is. It can also keep a constant record of its altitude and how fast it is moving. The ultralight pilots rely on their GPS receivers to tell them how far and how long they must fly before they get too their stopover sites. This lets them know if the birds can make it without tiring and needing to land. If a crane gets tired and drops out, the pilot can radio the location to ground trackers, who can then locate the "missing" bird with tracking equipment.

Try this! Journal or Discuss
  • Since the ultralight airplanes flying with the cranes have GPS receivers, why do you think each also has an altimeter and a speedometer?
  • Would the GPS receiver show the plane's ground speed or air speed? Why?
  • GPS receivers are on airplanes, buses, and many cars. When have you been in a car when a GPS could be helpful?

Journey North is pleased to feature this educational adventure made possible by the Whooping Crane Eastern Partnership (WCEP).