Digital PSAT Reading and Writing Practice Question 107: Answer and Explanation

Question: 107

The intrinsic difficulty of predicting a comet's greatness makes the consistency of Halley's visibility even more remarkable. Most great comets will pass near Earth only once every several thousand years, whereas Halley's does so on a cycle of about seventy-five years-making it the only great comet with the potential to appear twice in a human lifetime. With an eccentricity of 0.967, the orbit of Halley's Comet is extremely elliptical; at one end of its major axis Halley's is roughly the same distance from the sun as Pluto, whereas at the other it passes between the orbits of Mercury and Venus. The highly elliptic character of Halley's orbit means that, apart from having one of the highest velocities of any body in our solar system, it passes near Earth both during its approach and its return from the sun.

Which choice best states the main purpose of the text?

• A. Discuss the physical definition of elliptical eccentricity
• B. Provide scientific justification for the rarity of Halley's predictable visibility
• C. Give historical evidence of human observation of Halley's velocity
• D. Differentiate Halley's from other celestial bodies, such as planets and meteors

Correct Answer: B

Explanation:

(B) The author uses this text to give scientific reasons, such as Halley's unusually elliptical orbit, as to why Halley's Comet is a uniquely observable comet. The other options do not give you the primary purpose of the text, just minor things that are mentioned.