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a stellar system
Stellar Systems 101, by Dr. Markus Janson
by Dunlap Institute
Although our own Solar system only contains one star, many stellar systems include two stars (binaries), or an even greater number of stellar components. In this lecture, I discuss the variety of architectures of stellar systems, addressing questions such as what fraction of stellar systems are multiple, and how the stars in a multiple system orbit each other. Emphasis will be put on explaining Kepler's laws of celestial motion, which can be used as a basis to understand the orbits of everything from stars to planets to moons and man-made satellites. Finally, I examine how the study of binary systems has been, and remains, crucial to the determination of the fundamental properties of stars.