A meteor stream is composed of dust particles that have been ejected from a parent comet at a variety of...
GMAT Reading Comprehension : (RC) Questions
A meteor stream is composed of dust particles that have been ejected from a parent comet at a variety of velocities. These particles follow the same orbit as the parent comet, but due to their differing velocities they slowly gain on or fall behind the disintegrating comet until a shroud of dust surrounds the entire cometary orbit. Astronomers have hypothesized that a meteor stream should broaden with time as the dust particles' individual orbits are perturbed by planetary gravitational fields. A recent computer-modeling experiment tested this hypothesis by tracking the influence of planetary gravitation over a projected 5,000-year period on the positions of a group of hypothetical dust particles. In the model, the particles were randomly distributed throughout a computer simulation of the orbit of an actual meteor stream, the Geminid. The researcher found, as expected, that the computer-model stream broadened with time. Conventional theories, however, predicted that the distribution of particles would be increasingly dense toward the center of a meteor stream. Surprisingly, the computer-model meteor stream gradually came to resemble a thick-walled, hollow pipe.
Whenever the Earth passes through a meteor stream, a meteor shower occurs. Moving at a little over 1,500,000 miles per day around its orbit, the Earth would take, on average, just over a day to cross the hollow, computer-model Geminid stream if the stream were 5,000 years old. Two brief periods of peak meteor activity during the shower would be observed, one as the Earth entered the thick-walled "pipe" and one as it exited. There is no reason why the Earth should always pass through the stream's exact center, so the time interval between the two bursts of activity would vary from one year to the next.
Has the predicted twin-peaked activity been observed for the actual yearly Geminid meteor shower? The Geminid data between 1970 and 1979 shows just such a bifurcation, a secondary burst of meteor activity being clearly visible at an average of 19 hours (1,200,000 miles) after the first burst. The time intervals between the bursts suggest the actual Geminid stream is about 3,000 years old.
The primary focus of the passage is on which of the following?
1. Passage Analysis:
Progressive Passage Analysis
| Text from Passage | Analysis |
|---|---|
| A meteor stream is composed of dust particles that have been ejected from a parent comet at a variety of velocities. | What it says: A meteor stream = bunch of dust particles shot out from a comet at different speeds What it does: Introduces the basic concept and main components Source/Type: Scientific fact/definition Connection to Previous Sentences: First sentence - establishes foundation Visualization: Imagine a comet shooting out dust particles - some at 10 mph, some at 15 mph, some at 20 mph. These particles form what we call a "meteor stream." What We Know So Far: Meteor streams are collections of dust from comets What We Don't Know Yet: What happens to these particles over time |
| These particles follow the same orbit as the parent comet, but due to their differing velocities they slowly gain on or fall behind the disintegrating comet until a shroud of dust surrounds the entire cometary orbit. | What it says: The dust particles travel the same path as their comet, but because they move at different speeds, they spread out around the whole orbit What it does: Explains what happens to the particles over time - they spread out Source/Type: Scientific fact/observation Connection to Previous Sentences: This builds directly on sentence 1 by explaining what happens to those "dust particles at different velocities" - they spread out around the orbit Visualization: Picture cars on a racetrack all starting together but driving at different speeds (60 mph, 65 mph, 70 mph). Eventually, they'll be scattered all around the track, with faster cars ahead and slower cars behind. Reading Strategy Insight: This is helpful elaboration, not new complexity - we're just learning what happens next to the particles we already know about |
2. Passage Summary:
Author's Purpose:
To explain how scientists used computer modeling to test and confirm a new understanding of meteor stream structure, showing that streams develop a hollow pipe shape rather than the dense center that was previously expected.
Summary of Passage Structure:
In this passage, the author walks us through a complete scientific discovery process:
- First, the author explains what meteor streams are and introduces the scientific hypothesis that they should broaden over time due to planetary gravity.
- Next, the author describes how scientists tested this hypothesis using a computer simulation of the Geminid meteor stream over 5,000 years.
- Then, the author reveals the surprising results - while streams do broaden as expected, they develop a hollow pipe structure instead of having dense centers, and explains what this would mean for observable meteor showers on Earth.
- Finally, the author shows that real observational data from the Geminid meteor shower confirms the computer model's predictions, proving the hollow pipe theory is correct.
Main Point:
Computer modeling has revealed that meteor streams develop an unexpected hollow pipe structure over time, and this discovery has been confirmed by real observational data, giving scientists a new understanding of how these cosmic phenomena actually work and allowing them to determine the age of meteor streams.
3. Question Analysis:
The question asks for the "primary focus" of the passage, which means we need to identify the main purpose or central theme that unifies the entire passage. This is asking us to step back and see the big picture of what the author is trying to accomplish.
Connecting to Our Passage Analysis:
From our progressive analysis, we can see the passage follows a clear scientific narrative:
- Introduction of hypothesis - Scientists theorized that meteor streams broaden over time due to planetary gravity
- Description of new model - Computer modeling tested this hypothesis and revealed an unexpected hollow pipe structure
- Testable predictions - The model predicted twin-peaked meteor shower activity
- Confirmation through observation - Real Geminid data from 1970-1979 confirmed the model's predictions
- Scientific application - The model was used to determine the actual age of the Geminid stream
The passage analysis shows this is fundamentally about describing a new theoretical model (the hollow pipe structure) and demonstrating how it explains observed phenomena (the twin-peaked Geminid meteor showers).
Prethinking:
The primary focus is on presenting a new theoretical model that emerged from computer simulation - the hollow pipe structure of meteor streams - and showing how this model successfully explains real observational data. The author spends significant time describing both the model's unexpected findings and how those findings match actual observations, making this a story about a new model that explains natural phenomena.
Why It's Wrong:
• The passage doesn't compare two competing theories - it describes one theoretical expectation (dense center) being replaced by a new model (hollow pipe)
• The focus isn't on contrasting predictions but on showing how a new model explains observations
• The passage presents a linear scientific discovery, not a comparison of rival theories
Common Student Mistakes:
1. Did I misinterpret the mention of "conventional theories" as presenting two competing theories?
→ The "conventional theories" are mentioned only to show they were wrong; the passage focuses on the new computer model that replaced them
2. Am I confusing the structure with a comparative analysis?
→ Focus on what gets the most attention - the new hollow pipe model and its confirmation, not theory comparison
Why It's Right:
• The passage centers on describing the computer model that revealed the hollow pipe structure of meteor streams
• It shows how this model explains the observed twin-peaked activity in actual Geminid meteor showers
• The entire narrative is built around presenting this new model and demonstrating its explanatory power
• The author devotes significant space to both describing the model and showing how it matches real observations
Key Evidence: "Surprisingly, the computer-model meteor stream gradually came to resemble a thick-walled, hollow pipe" followed by "The Geminid data between 1970 and 1979 shows just such a bifurcation, a secondary burst of meteor activity being clearly visible" - this shows the new model and its confirmation through observations.
Why It's Wrong:
• The passage doesn't evaluate experimental results in a critical way or suggest areas for further research
• The results are presented as successful confirmation of the model, not as something requiring evaluation
• There are no suggestions for future research directions
Common Student Mistakes:
1. Does the mention of computer modeling make this about evaluating experiments?
→ The computer modeling is a tool used to create the theoretical model; the focus is on the model itself, not evaluating the experimental methodology
2. Is the comparison with real data an evaluation of results?
→ This is confirmation/validation of the model, not critical evaluation suggesting further research
Why It's Wrong:
• The passage focuses on one phenomenon (meteor streams) and how a model explains it, not on relating two different phenomena
• While it mentions measuring stream age, that's a byproduct of the model, not the primary focus
• The passage doesn't demonstrate measurement techniques as its main purpose
Common Student Mistakes:
1. Are meteor streams and meteor showers two different phenomena being related?
→ Meteor showers are simply what we observe when Earth passes through meteor streams - they're the same phenomenon observed from different perspectives
2. Is determining the stream's age a form of measurement that's central to the passage?
→ The age determination is mentioned only in the final sentence as an application, not as the primary focus
Why It's Wrong:
• The passage starts with a theoretical model from computer simulation, then checks it against observational data
• The structure is model → prediction → observation, not observation → model construction
• The Geminid observational data is used to confirm an existing model, not to construct a new one
Common Student Mistakes:
1. Since real Geminid data is discussed, isn't this about analyzing observational data first?
→ The real data appears at the end to confirm the computer model; the model came first, then was tested against observations
2. Does using data to determine stream age count as constructing a model?
→ The model already existed; the data just provides parameters (age) for the existing hollow pipe model