AST101H1 Chapter Notes - Chapter 1: Galactic Center, Observable Universe, Edwin Hubble
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AST101H1 Full Course Notes
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Earth is a planet in our solar system. The sun and all the stars we can see with the naked eye make up only a small part of a huge, disk-shaped collection of stars called the milky way galaxy (more than 100 billion stars) A galaxy is a great island of stars in space, containing from a few hundred million to a trillion or more stars. Milky way is one of the two largest among about 40 galaxies in the local group. Groups of galaxies with more than a few dozen members are often called galaxy clusters. The regions in which galaxies and galaxy clusters are most tightly packed are called superclusters. The universe is the sum total of all matter and energy, encompassing the superclusters and voids and everything within them. Expansion of universe occurred about 14 million years ago. The point at which the expansion of universe began is called the big bang.