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Then Hubble discovered the universe was expanding. Let me take a moment to explain how he did that. When you look at a star you see a bunch of light. If you put that light through a glass prism, you get a rainbow of color. But some lines are missing, like in the 1st picture. These missing lines come from where the light has passed through the gas around the star and gotten caught up in it. So those lines don’t make it all the way to us. When the star that the light came from is moving away or towards us those lines shift either to more red (if the star is moving away) or more blue (if the star is moving towards us). Hubble found several things when he started looking at the shifts of a whole bunch of stars. First he found that most stars had red shifts, in other words, most stars where moving away from us. This lead Hubble to conclude that the universe was expanding. Second, he looked only at the stars that he knew the distance to. Then he made a chart of how much they shifted. This is what we see in the second picture. Each dot is a star, the speed on the graph corresponds to how much a star shifts and the distance is how far away the star is. Hubble had actually discovered that if we knew how fast a star was going away from us we could figure out how far away from us it was. Suddenly we had a whole new way to find how far away stars were!
Then Hubble discovered the universe was expanding. Let me take a moment to explain how he did that. When you look at a star you see a bunch of light. If you put that light through a glass prism, you get a rainbow of color. But some lines are missing, like in the 1st picture. These missing lines come from where the light has passed through the gas around the star and gotten caught up in it. So those lines don’t make it all the way to us. When the star that the light came from is moving away or towards us those lines shift either to more red (if the star is moving away) or more blue (if the star is moving towards us). Hubble found several things when he started looking at the shifts of a whole bunch of stars. First he found that most stars had red shifts, in other words, most stars where moving away from us. This lead Hubble to conclude that the universe was expanding. Second, he looked only at the stars that he knew the distance to. Then he made a chart of how much they shifted. This is what we see in the second picture. Each dot is a star, the speed on the graph corresponds to how much a star shifts and the distance is how far away the star is. Hubble had actually discovered that if we knew how fast a star was going away from us we could figure out how far away from us it was. Suddenly we had a whole new way to find how far away stars were!
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