Classified as a Cepheid Variable and About 500 to 800 Light-Years from Earth, Polaris, the North Star, has Long been known as a Pulsating Star.

Reading Passage Question

Classified as a Cepheid variable and about 500 to 800 light-years from Earth, Polaris, the North Star, has long been known as a pulsating star that dims and then brightens approximately every four days. If new findings are correct, Polaris now appears to be changing into a star whose brightness remains constant, providing scientists the unique opportunity to witness sidereal evolution. The latest observations apparently point to the cessation of pulsations within a few years. The results of these studies also suggest that the four-day pulsation period is slowly lengthening, and establish that this decline is occurring gradually rather than by abrupt jumps, slowing as the star ages, cools, and expands. More surprisingly, the pulsations themselves--even as they slow down--now appear to be fading away. This drop in amplitude suggests a cessation of the internal conditions that drive the pulsations will result in a disappearance of the pulsations.

Current interpretation suggests that we may be observing the star as it moves out of its phase of pulsational instability. Cepheids spend 40,000 years or more in an unstable, pulsating phase before reaching non-pulsing stability, and accordingly, the chance of observing a star during its transition, which lasts only a short time, is small. Rare as this event may be, it provides the most logical explanation of the decline in both the frequency and the amplitude of the star’s pulsations.

“Classified as a Cepheid variable and about 500 to 800 light-years from Earth, Polaris, the North Star, has long been known as a pulsating star.”- is a GMAT reading comprehension passage with answers. Candidates need a strong knowledge of English GMAT reading comprehension.
This GMAT Reading Comprehension consists of 7 comprehension questions. The GMAT Reading Comprehension questions are designed for the purpose of testing candidates’ abilities in understanding, analyzing, and applying information or concepts. Candidates can actively prepare with the help of GMAT Reading Comprehension Practice Questions.

Solution and Explanation

1. The primary purpose of the passage is to

1. refute the conventional explanation for the stellar behavior of Polaris
2. provide an interpretation of recently observed phenomena
3. present evidence that confirms an unorthodox theory
4. confirm the value of a recent research project
5. defend an established theory against unwarranted attacks

2. According to the passage, the pulsations of a Cepheid variable most probably cease

1. when the star is no more than 40,000 years old
2. soon after the interior forces creating pulsation cease
3. as the star enters its transformational phase
4. with the onset of cooling and expansion
5. when the star's pulsation period shortens to fewer than four days

3. The author mentions that Polaris is aging, cooling and expanding in order to

1. describe the definitive characteristics of stars classified as Cepheid variables
2. explain the importance attached to the study of Polaris
3. describe the effects that internal conditions have on the brightness of Polaris
4. provide an explanation for the incremental lengthening of the star's pulsations
5. raise doubts about the traditional description of Polaris as stable

4. It can be inferred from the passage that the author believes which of the following about Cepheid variables?

1. They are often a part of major constellations.
2. Their pulsations are difficult to detect.
3. They eventually reach a stable, non-pulsating state.
4. They are fewer than 800 light-years from the earth.
5. They undergo a lengthy transition between phases.

5. The author would most likely argue that which of the following descriptions is most analogous to the gradually slowing pulsations of Polaris?

1. Water in a beaker contract as it cools until it reaches a point just above freezing, after which it begins to expand, and continues to expand through its phase change into ice.
2. The echo off a canyon wall takes longer to return to a listener as the origin of the noise moves further away from the wall.
3. A tuning fork is struck, giving off a high-pitched tone, and the pitch gets lower as the vibration of the tines slows over time.
4. An unevenly weighted lump of clay begins to rotate in an eccentric manner as a potter's wheel increases its speed of revolution.
5. The earth's moon goes through a nightly cycle of becoming more visible until it is in its full phase, and then incrementally wanes until it is no longer visible.

6. The passage suggests that all of the following are accurate statements about Polaris EXCEPT

1. Its distance from the earth has not been precisely established.
2. Its pulsations are now longer than the four-day period previously recorded.
3. It can be located in the Northern hemisphere of the night sky.
4. The amplitude of its pulsations has been declining for 40,000 years.
5. Its current transition status is a comparatively brief phase.

7. The passage suggests that the pulsations of Polaris can be expected to

1. continue to decline in both frequency and amplitude as the star becomes more stable
2. continue at the current rate of frequency and degree of amplitude indefinitely
3. build in frequency and drop in amplitude until the star reaches a stable state
4. increase in both frequency and amplitude as the star leaves its unstable phase
5. remain perceptible and stable for at least 40 QO0 years while internal forces cease

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