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NASA
Nasa: The Space Place: Orbits 'R' Us
Learn about how Earth orbits the sun and how satellites orbit the Earth. Discover the different types of satellites such as GOES and POES and what they are used to monitor.
NASA
Nasa: The Space Place: What's a Barycenter?
This site from NASA helps in explaining a barycenter. "In the case of the Earth and the Sun, both bodies actually revolve, or spin, around the center of the mass between them. This point is called the barycenter."