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PHYS 183 (60)
Tracy Webb (34)
Lecture 20

Lecture 20

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McGill University
PHYS 183
Tracy Webb

th Lecture 20: February 25 , 2013  review from 1 week ago (no class last Wednesday or Friday): o HR diagrams show every single star we are aware of in the universe & show the temperature, colour, luminosity, radius, mass & lifetime of the stars o there are 4 luminosity classes, supergiants, giants, main sequence & white dwarfs o the sun will live for about 10 billion years (it has already gone through 5 billion years) o mass determines everything about a star o more mass = hotter core = faster burning of H  there is pressure pushing outwards from the core due to energy and light, and gravity pushing into the core of a star  there is an ongoing war between pressure and gravity  H fusion helps keep this balance, but when H runs out, there is no longer a balance (less pressure)  when the hydrogen in the core of a star runs out, the core contracts/heats up & outer layers puff o the core contracts because gravity has won the war over pressure since fusion is no longer producing pressure  moving from the main sequence: o running out of H in the core o new fusion reactions  creates a helium burning
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