AST201H1 Lecture Notes - Lecture 1: Vera Rubin, Spiral Galaxy, Orbital Speed
19 Jan 2019
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One patch of the night sky can have numerous galaxies. If you are looking at things in the sky, it actually means you are looking back in time, as light takes time to travel and reach us. Thus, the farther you look in space, the further back in time you are actually looking at. The distant galaxies one can see are actually not seen as they are right now. Instead they are what they looked like 5-9 billion years ago. Back in the 1920"s, it was thought that most of the universe was things you could actually see like stars, planets, galaxies, gas, dust etc. Fritz zwicky (1898-1974) he said that you can know what is in the universe by looking at the gravitational force of things. He realized that there are more things in the universe as the force is greater than the number of stars in the sky.
