AST201H1 Lecture Notes - Lecture 23: Main Sequence, Cosmic Distance Ladder, Edwin Hubble
30 Mar 2019
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The stars all have the same age and the stars are all at around the same distance. They are all at around the same distance. Step 1: use radar to determine the size of the earth"s orbit. Step 2: use parallax to determine the distance to objects within the milky way. Idea 1: the universe is eternal and unchanging with no beginning, and no end. Idea 2: the universe was created by god, around 6,000 years ago. These were dominant ideas in the early 20th century. If the universe is infinite and unchanging, you should be able to see a star eventually no matter where you look. If we know the spectral type of a star and we know it is a main sequence star then we can use the hr diagram to look up it"s luminosity! Step 3 of the distance ladder: use main sequence fitting to compare the distance from nearby clusters to distant ones.
