PT128.S4.P3.Q15

PrepTest 128 - Section 4 - Passage 3 - Question 15

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 astronomers. But eventually it was accepted by them.

Evidence supporting old perspective

• Known asteroids contain iron
• 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

Payne's interpretation of evidence

• Spectroscopic data consistent with sun being 90% hydrogen and the rest mostly helium

Astronomers' response

• Payne was looking only at outer layer of sun

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.

Question Type

• Implied

The author describes the reaction of scientists to Payne’s interpretation at the end of P3: “Most astronomers at the time dismissed Payne's interpretation, and 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.”

Analysis

• The methodology she used was not considered outdated. Although most dismissed her interpretation, that doesn’t imply they thought her methodology was outdated.

Difficulty

• Passage is moderately difficult.