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passage 3
P1
In the early 1900s, most astronomers mistakenly believed that 66 percent of the sun's substance was iron. ███
Old perspective ·
Sun was mostly made of iron
Payne's perspective ·
Sun is mostly hydrogen and helium
Payne's view initially was resisted by astronmers. But eventually it was accepted by them.
P2
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Evidence supporting old perspective ·
Known asteroids contain iron, and spectroscopy
Spectroscopy involves identifying chemical from light patterns. This seemed to show that sun was mostly iron.
Puzzling aspect of old perspective ·
How could something made mostly of iron generate the high energy output of the sun?
Kelvin's answer ·
Sun was contracting, which raised sun's temperature and generated energy
Payne's response ·
Fossil record showed Kelvin's answer was wrong; need to re-examine the iron theory
If sun contracted as Kelvin said, the sun would be much younger than fossil record showed it was. So, iron theory might be wrong and we need to look at the spectroscopic evidence again.
P3
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Payne's interpretation of evidence ·
Spectroscopic data consistent with sun being 90% hydrogen and the rest mostly helium
Although sun has some iron, preconceptions about sun being iron led to prior interpretation that sun was mostly iron.
Astronomers' response ·
Payne was looking only at outer layer of sun
P4
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Confirmation of Payne's perspective ·
Later discovery of nuclear fusion helped confirm Payne was right
During Payne's time, we didn't know how something mostly helium/hydrogen could produce as much energy the sun. Now, we know that the sun's energy is produced by nuclear fusion.
Passage Style
Critique or debate
Phenomenon-hypothesis
18.
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a
Its use during ███ █████ ███ █████████ ████████ ██ ███ █████ ██ ██████████
b
It yielded data █████ ███ █████ ███████████ ████ █████ █████████ ███████ ███ ██████████ ████ ██ ███████
c
It played a ████████ ██████ █████ ███████████████ ████ ██ ███ █████████ ██ ███ ███████████ █████████████ ██ ███ ███████ ██ ███████ ███████
d
It was regarded ██ ███████ █████████ ██████████ ██ ███ █████ ██ ██ ████████ ████ ████ ████████ ████ ██ █████ ████████████ ████████████
e
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