Gravity videos (i.e., Gravity videos):
1. Sun, earth, moon animation | 0:39: This illustrates Earth-Moon system orbiting the Sun. It is not-to-scale. The mutual gravitational attraction of the the Earth and Moon cause them to orbit their mutual center of mass (AKA their barycenter). The mutual gravitational attraction of all the bodies of the Solar System cause them to orbit the Solar-System barycenter which is always inside or near the Sun (see Wikipedia: Heliocentric orbit). The Solar System itself orbits the barycenter of the Milky Way which is nearly at the center of the Milky Way. One can view the Solar System as a point mass located at its barycenter for just considering barycenter motions as determined by net external forces via Newton's 2nd law of motion (AKA F=ma). Note virtually all bodies rotate as well as orbit in the astrophyical realm. Good for the classroom.
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