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Tuesday, April 2, 2013

Out of this World -- Sort Of

The geographers at Bridgewater State University are fortunate to have good relationships with geographers around the world. One of these is Dr. Francisco Henrique de Oliveira of the University of the State of Santa Catarina in Florianopolis, Brazil. As a specialist in surveying and mapping, he shares many interesting stories and images related to geotechnology.

He recently shared this graphic, which compares seven satellite orbits, including those of the International Space Station (ISS) and the the Global Positioning System (GPS). The highest orbit shown is the geostationary category, which includes a variety of satellites -- such as those used for television -- that need to stay in a constant position over the earth. (Learn more about GPS from our Where We Are post.)

We are working on exercises to compare these orbits at EarthView scale. For example each of the 24 satellites in the GPS system would orbit about 30 feet away from the surface of EarthView.

Please notice a few things about the diagram.

First, although it might seem to imply that all orbits run over the North and South Poles; this is not the case but simply makes the diagram readable.
Second, notice that the distances are expressed both as height above sea level and radius from the earth's center; the difference, of course, is the radius of the earth, about 4,000 miles.
Third, notice that the speed varies with height, with lower-orbiting satellites moving much faster than those at greater height.
Finally, notice that the time required to complete a full orbit increases with height; this is relationship between increased circumference and decreased speed as height increases.

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