Copernicus first theorized that the Sun was the center of our solar system, but it took the work of Johannes Kepler to prove it. Learn why the universe is expanding and meet modern astronomers who gauge the likelihood of life out there.
Part 2: http://youtu.be/YZAf1IdP7Gkz
Part 3: http://youtu.be/FijAewRrD-8
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