Event 91


10 091 001constellation gps
This is an animated image of 24 satellites orbitting earth, 4 satellites for each of 6 orbits. A half a minute of animation is equivalent to 24 hours.
Credit: Image by EI Pak, Courtesy of Wikipedia.

One of the major everyday practical benefits of the space program (besides Teflon!) has been the use of orbiting satellites for global communication (satellite TV, weather forecasting, long-distance phone calls) as well as being able to find out precisely where you are on the earth. By triangulating your position with a global positioning device (now built into most modern cell phones), using at least four GPS satellites, you can presently pinpoint your location to astonishing degree of precision and tell what time it is. And with such tools as Google Earth, you can see detailed satellite images of your house, your street, cities, and natural wonders such as the Grand Canyon and Mount Everest.

The development of modern GPS has long and deep roots in navigation systems going back to World War II. Much of the development of the United States GPS system was developed by the U.S. military, and for many years its use for civilian purposes was severely restricted, with the signal deliberately degraded for nonmilitary users. GPS satellite launches began in 1990, and now there more than two dozen in orbit and operating. Since the restrictions on civilian use (“Selective Availability”) were removed by Presidential order in 2000, the use of GPS now pervades our everyday lives for many of us on the planet, permitting us (and sometimes others!) to know where we are almost anywhere we go, providing maps and directions on handheld devices such as our phones, and even letting us find out what restaurants and movies are nearby in real time. GPS is operated and owned by the U.S. Government, but other countries and organizations such as Russia, China, and the European Union have also been developing their own systems for such purposes.


10 091 002gps-device
Photo of TomTom One global positioning system (GPS) car navigation device (2006).
Credit: Image by Darrenm540, Courtesy of Wikipedia.


The U.S. government operates and owns the Global Positioning System.  The research and development that made the GPS possible was publicly funded by tax dolloars, but it not only serves government and public interests, it has spurred a huge industry that has benefited the private sector and the economy of this country. Such global positioning systems can help people find their way when hiking or driving, can help ships and planes navigate their courses, are essential in military and political intelligence, and can direct military ordinance to their targets with pin-point precision. 




This is a U.S. government website. It discusses GPS technology and includes a general overview of uses in the military, business, and travel spheres. There is also a GPS Adventures game to teach kids and adults about GPS technology.

This website provides a daily view of the Earth via satellite imaging, including an archive of every single day since the site’s launch.

This is from NASA’s global imaging technologies: a snapshot of the earth at night. I like it because the concentration of light around the world is fascinating.




Go back to overview of Time Scale 9

Go back to Event 90

Comments are closed.