During the Past 40 Years The Star FG Sagittae has Changed Color from Blue to Yellow GMAT Reading Comprehension

Reading passage questions

This passage is based on an article written in the mid-1990s.

During the past 40 years, the star FG Sagittae has changed color from blue to yellow—direct evidence that its temperature has dropped dramatically. Its cooling is probably due to a rapid increase in its size, an inference that is indirectly supported by two independent pieces of observational evidence. Like many stars, FG Sagittae rhythmically pulsates, beating like a heart, and over the past 30 years the period of this pulsation has noticeably lengthened. Given that a star's pulsation period is determined by its radius, FG Sagittae must have gotten larger. Moreover, FG Sagittae's total luminosity—the amount of light it emits over all wavelengths—has been observed to remain constant despite the star's plummeting temperature. It is known that a star's luminosity is the product of its temperature and its radius multiplied together: if one of the two factors has decreased while over the same period luminosity has remained constant, the other factor must have increased.

One interesting sidelight: even though the total amount of light FG Sagittae emits has not changed, the star now appears brighter in the sky than it did 40 years ago. Then, being a blue star, it emitted most of its light at ultraviolet wavelengths, and ultraviolet light is invisible to human eyes.

During the Past 40 Years The Star FG Sagittae has Changed Color from Blue to Yellow GMAT Reading Comprehension is a GMAT reading comprehension passage with answers. Candidates need a strong knowledge of English GMAT reading comprehension. This GMAT Reading Comprehension consists of 3 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. According to the passage, if the luminosity of a given star has remained constant while its temperature has decreased, what will also necessarily be true of the star?

(A) The star will have increased in size.
(B) The star's apparent brightness will have substantially increased.
(C) The star will have changed from blue to yellow in color.
(D) The star's pulsation period will have shortened somewhat.
(E) The star will have begun to emit less visible light than it once did.

Answer: (A) The star will have increased in size.
Explanation
: It can be seen in the passage that a star's luminosity is the product of its temperature and its radius multiplied together. So if one of the two factors has decreased while over the same period luminosity has remained constant, the other factor must have increased. Hence option A is the correct answer.

  1. It can be inferred from the passage that the phrase “two independent pieces of observational evidence” (see highlighted text) refers to observations made of which of the following?

(A) FG Sagittae's apparent brightness in the sky and its temperature
(B) FG Sagittae's color and its temperature
(C) The amount of light FG Sagittae emits across all wavelengths and its pulsation period
(D) FG Sagittae's radius and its color
(E) The amount of light FG Sagittae emits across all wavelengths and the amount it emits at ultraviolet wavelengths

Answer: (C) The amount of light FG Sagittae emits across all wavelengths and its pulsation period
Explanation
: It is evident that two independent pieces of observational evidence are stated in the given passage. FG Sagittae states that a star's pulsation period is determined by its radius. FG Sagittae's total luminosity is the amount of light it emits over all wavelengths. Hence option C is the correct answer.

  1. The author of the passage is primarily concerned with

(A) analyzing the effects of a particular phenomenon
(B) presenting evidence in favor of a given explanation
(C) reporting new data that undermines an accepted view
(D) evaluating the arguments in favor of a given hypothesis
(E) presenting an interesting sidelight on a complex phenomenon

Answer: (B) presenting evidence in favor of a given explanation
Explanation
: In the first paragraph, the author states about a phenomenon called star FG Sagittae. It has changed color from blue to yellow. This provides an explanation of the direct evidence that its temperature has dropped dramatically. He later adds more evidence that supports the given explanation in the rest of the paragraph.

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