What is GPS and Activity 1

What is GPS and Activity 1 - (Student) What is a GPS? GPS...

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2 (Student) What is a GPS? GPS is an abbreviation for Global Positioning System. Have you ever spent an evening staring at the stars and saw something that was moving (so it wasn’t a star), but moving too slow (so it wasn’t a plane)? Well, it may have been a satellite. It turns out there are quite a number of satellites out there in space. They are used for a wide range of purposes; satellite TV, cellular phones, military purposes and etc. Satellites can also be used by GPS units. Have you ever been shopping in a mall or a large department store and had a hard time finding your way? Maybe you were lucky enough to find one of those mall directory maps. Remember how handy it was to find that star labeled “you are here?” Then it was as if the whole layout made sense, and you didn’t have to orient yourself anymore. Well, a GPS unit is a lot like that handy star, but on a much bigger scale. GPS units are made to communicate with those moving satellites (which have a much better view of the Earth) to find out exactly where they are on the global scale of things. When you are holding a unit, it’s as if the satellites are making a “you are here” star for you on a global map. The way they do it is neat. First of all, let’s say a GPS unit communicates with one satellite. The satellite gives off a signal to a GPS, and because the satellites are in a locked (known) orbit, the GPS unit is able to calculate where it is in relation to the satellite. If it’s only one satellite that the GPS is
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3 communicating with, then at best it can only make a very large “you are here” star (or circle as in our diagram). However, if another satellite is locked on for communication, that would be two large circles we can draw, and we know that our “you are here” star fits in where those two circles overlap. What if we could get three satellites to communicate with, or four? It turns out that the more circles we can draw, the more specific we can be at placing our star. Do you see how small our star is? That means we’re pretty sure about its exact location. So, the more satellites we have, the more sure we are about the placement of our star. It usually takes communication with at least four satellites for us to be confident about our star location. Even if we had every satellite in the sky communicating with us, though, we would still end up with a circle that surrounds our star with plus or minus five meters. Some GPS units are able to limit the size of their circles to one centimeter! The GeoExplorer 3 that we are using, however, is only able to do it to about five meters or so, which is just fine for all of our purposes.
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4 Sometimes signals come in from satellites, and they’re not following a crisp line. Have you ever put a pencil in a clear glass of water? Did you notice that where the pencil touched the water it seemed to be bent? Did you pull the pencil out just to reassure yourself that it wasn’t messed up? You probably saw that it was straight as could be. So why did it bend when it was in the water?
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What is GPS and Activity 1 - (Student) What is a GPS? GPS...

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