Examkin

Question

Difficulty: EasyMain Idea and Primary Purpose

Passage:
For early twentieth-century astronomers, interstellar space was largely conceived as an unmeasurable void, primarily because optical telescopes could not penetrate the dense clouds of cosmic dust that obscured the Milky Way’s galactic plane. The advent of radio astronomy in the 1930s initially met with skepticism from a discipline entrenched in visual observation. However, the theoretical prediction of the 21-centimeter neutral hydrogen spectral line by H. C. van de Hulst in 1944, followed by its experimental detection by Harold Ewen and Edward Purcell in 1951, fundamentally transformed observational astrophysics. Rather than merely confirming the existence of interstellar gas, the detection of the 21-centimeter line provided astronomers with a powerful diagnostic tool capable of mapping the spiral structure of the Milky Way through cosmic dust clouds. Consequently, radio astronomy transitioned from a peripheral engineering curiosity to a central discipline of modern astrophysics. By demonstrating that non-optical electromagnetic radiation could unveil previously invisible galactic structures, Ewen and Purcell’s empirical breakthrough invalidated the assumption that optical observational boundaries defined the limits of cosmic inquiry.

Based on the passage, which of the following statements accurately express the main idea or primary purpose of the text? Select all that apply.

  1. To explain how the empirical detection of the 21-centimeter neutral hydrogen line established radio astronomy as a core astrophysical discipline by overcoming the observational constraints of optical astronomy.Answer
  2. To argue that advances in non-optical astronomy invalidated the belief that galactic structure could only be investigated within the limits of optical observation.Answer
  3. C
    To provide a technical comparative analysis of the optical mechanics of early telescopes versus mid-twentieth-century radio receivers.
  4. D
    To demonstrate that early twentieth-century astronomers rejected theoretical physics due to institutional hostility toward non-visual methodologies.
  5. E
    To contend that H. C. van de Hulst's 1944 theoretical work was inaccurate until Ewen and Purcell corrected his mathematical models in 1951.

Answer

The main idea and primary purpose are accurately expressed by the statements asserting that the detection of the 21-centimeter line established radio astronomy as a core discipline by overcoming optical limitations, and that non-optical breakthroughs invalidated the assumption that optical observation defined the boundary of cosmic inquiry.
The correct options reflect the central argument of the passage: the experimental detection of the 21-centimeter neutral hydrogen line allowed astronomers to map the Milky Way through cosmic dust, elevating radio astronomy to a primary discipline and proving that cosmic exploration extends beyond optical boundaries.

Step-by-Step Solution

1
Analyze the passage structure and central thesis.
The text describes how early reliance on optical telescopes limited galactic mapping due to cosmic dust, and explains how the 1951 detection of the 21-cm line transformed radio astronomy from a peripheral field into a primary discipline capable of probing previously hidden galactic structures.
Identifying the overarching narrative arc distinguishes the central claims from supporting details.
2
Evaluate each option against the identified primary claims.
The choices regarding the elevation of radio astronomy into a central discipline and the invalidation of optical observational boundaries directly align with the core arguments of the passage.
Options expressing the primary purpose must accurately summarize the main claims without introducing unsupported extrapolations or narrow detail shifts.

Key Concept

Identifying the central claim and primary purpose of an academic passage.
Estimated Time:1m 30s
Rate this question

Topics

Main Idea and Primary Purpose

More questions from this topic