The north celestial pole (NCP)—the fixed point around which stars in the Northern Hemisphere (including the Sun) appear to rotate—is...
GMAT Craft and Structure : (Structure) Questions
The north celestial pole (NCP)—the fixed point around which stars in the Northern Hemisphere (including the Sun) appear to rotate—is discernible only at night. Inspired by the navigational strategies of some insects and birds, researchers devised a method for locating the NCP in daytime using skylight polarization, which occurs as atmospheric particles scatter sunlight. A polarimetric camera captures images of polarization patterns, which rotate as the Sun's position in the sky changes; temporal variances across images can then be used to determine an observer's latitude and bearing relative to the NCP.
Which choice best describes the overall structure of the text?
It illustrates how most navigational tools utilize the NCP, recounts how researchers discovered that certain animals are able to navigate without using the NCP, and then proposes that this discovery could be used to avoid problems in navigation associated with reliance on the NCP.
It presents a celestial-based method of navigation, enumerates the comparative benefits of an alternative method used by certain animals that is based on an unrelated natural occurrence, and then indicates how researchers assessed the relative accuracy of the two methods.
It explains how the NCP is typically located, emphasizes a key difference between how humans and certain animals use the NCP for navigation, and then suggests an alternative way of using the NCP to improve existing navigational instruments.
It notes an obstacle to observing an astronomical phenomenon, mentions a navigational ability of certain animals that inspired a solution to that obstacle, and then explains how researchers used an optical device to mimic that ability.
Step 1: Decode and Map the Passage
Create Passage Analysis Table
| Text from Passage | Analysis |
|---|---|
| "The north celestial pole (NCP)—the fixed point around which stars in the Northern Hemisphere (including the Sun) appear to rotate—is discernible only at night." |
|
| "Inspired by the navigational strategies of some insects and birds, researchers devised a method for locating the NCP in daytime using skylight polarization, which occurs as atmospheric particles scatter sunlight." |
|
| "A polarimetric camera captures images of polarization patterns, which rotate as the Sun's position in the sky changes; temporal variances across images can then be used to determine an observer's latitude and bearing relative to the NCP." |
|
Provide Passage Architecture & Core Elements
Main Point: Researchers developed a daytime method for locating the north celestial pole by using skylight polarization, inspired by animal navigation strategies.
Argument Flow: The passage opens by establishing that the NCP can only be seen at night, which presents a navigational obstacle. It then explains how researchers, drawing inspiration from insects and birds, created a solution using skylight polarization. Finally, it details how this method works technically through a polarimetric camera that analyzes changing polarization patterns to determine location.
Step 2: Interpret the Question Precisely
What's being asked? The overall structure of the text - how the passage is organized and what each part does.
What type of answer do we need? A description of the passage's organizational pattern, showing how the ideas are arranged and connected.
Any limiting keywords? "Overall structure" tells us we need to capture the big picture flow of the entire passage, not just focus on specific details.
Step 3: Prethink the Answer
- The correct answer should capture three key elements: First, it should mention that there's an obstacle or limitation with the NCP (only visible at night)
- Second, it should reference the biological inspiration (insects and birds) that led to the solution
- Third, it should describe the technical solution involving the optical device (polarimetric camera)
- The passage follows a problem-inspiration-solution structure
It illustrates how most navigational tools utilize the NCP, recounts how researchers discovered that certain animals are able to navigate without using the NCP, and then proposes that this discovery could be used to avoid problems in navigation associated with reliance on the NCP.
✗ Incorrect
- Claims the passage illustrates how "most navigational tools utilize the NCP" which isn't what our passage does at all
- Says researchers discovered animals can navigate "without using the NCP" but the passage doesn't say this
It presents a celestial-based method of navigation, enumerates the comparative benefits of an alternative method used by certain animals that is based on an unrelated natural occurrence, and then indicates how researchers assessed the relative accuracy of the two methods.
✗ Incorrect
- Talks about "comparative benefits" between methods but the passage doesn't compare benefits
- Mentions researchers "assessed the relative accuracy of the two methods" but no accuracy assessment is discussed
It explains how the NCP is typically located, emphasizes a key difference between how humans and certain animals use the NCP for navigation, and then suggests an alternative way of using the NCP to improve existing navigational instruments.
✗ Incorrect
- Claims there's "a key difference between how humans and certain animals use the NCP" but the passage doesn't discuss how animals use the NCP
- Says it "suggests an alternative way of using the NCP to improve existing instruments" which isn't the focus
It notes an obstacle to observing an astronomical phenomenon, mentions a navigational ability of certain animals that inspired a solution to that obstacle, and then explains how researchers used an optical device to mimic that ability.
✓ Correct
- Matches our structure perfectly: "notes an obstacle" (NCP only visible at night)
- Captures the biological inspiration ("mentions a navigational ability of certain animals that inspired a solution")
- Describes the technical implementation ("explains how researchers used an optical device to mimic that ability")
- Follows the exact problem-inspiration-solution flow we identified