PrepTest 128 - Section 4 - Passage 3 - Question 19

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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.

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.

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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.

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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

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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 (RC)

19.

It can be inferred from ███████████ ██ ███ ███████ ████ ███ ██████████ ███ █████ ██ ███████ ████ ███████ ████████ ██ ████████ ████ ███ ███ ████████████ ███ █████████ ██ ███ ████ ███████ █████ ███ ██ ███ █████████ ██ ██ █████

Question Type

Implied

Other’s perspective

The scientists who tried to explain away Payne’s findings are described at the end of P3: “some sought to explain it away simply by claiming that what she had examined was data about the sun's outer surface rather than its interior.” These scientists assumed that Payne’s interpretation was correct about the outer surface, but wrong about the interior.

It is impossible ██ ████████ ████ ███████ ███████ ███████

No one knew about nuclear fusion during Payne’s time. So this wouldn’t be something the scientists assumed.

The inside of ███ ███ ██ ███ ██ ███ ████ ███████████ ██ ███ █████ ████████

This must be something the scientists assumed, because they thought Payne’s interpretation of the composition of the sun was correct about the outer surface but not the interior.

93%

The sun contained ████████████ ████████ ██ ████ ██████ █████ ███ ████████ ██ ██████

There was no generally accepted explanation for how hydrogen would produce the sun’s energy. The scientists weren’t aware that hydrogen could produce energy at all; their rejection of Payne’s data wasn’t due to a belief that there wasn’t enough hydrogen in the sun to produce enough heat.

Payne's preconceptions about ███ ██████ ██████████ ██████ ███ ████████ ██ █████████████ █████

We have no reason to think these scientists believed Payne’s analysis was biased.

Spectroscopy will not ██████ ███ ████████ ██ ████ ██ ███ ████ ██ ██ ██ ██████ ██ ███ ████ ████ █████ ██ ███ ███ ███

We have no reason to think these scientists believed spectroscopy couldn’t detect iron in an object as far away from the Earth as the sun is.

PrepTest 128 - Section 4 - Passage 3 - Question 19

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