Khan Academy Static

The universe is all the matter, energy, and space that exist. We can observe only a part of it--the observable universe. The entire, universe, including the part we cannot see, may be infinite. The observable universe contains as many as 100 billion galaxies and extends a billion light-years in every direction. The first five videos in this tutorial depict the different types of galaxies in our Universe, including spiral, giant and dwarf ellipticals. The interactions between these galaxy types are the subject of the five time-lapse simulations that follow. The last two videos describe two galactic phenomena: the Phoenix galaxy, which produces stars faster than any other known galaxy; and the formation of an elliptical galaxy 11 billion years ago, when two massive spiral galaxies merged.

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17324_Our_expanding_Universe.html

17321_Exploring_the_dark_Universe_Dark_matter.html

17322_Exploring_the_dark_universe_Dark_energy.html

17320_The_known_Universe.html