Hello, everyone! In our last lecture on TOEFL listening, we explored the formation of the asteroid belt through the lens of the nebular hypothesis. Today, we'll tackle another astronomical topic, this time drawn from a TOEFL reading passage. It's all about comets! We'll go over both the reading strategies and problem-solving strategies you'll need to conquer this topic.
Let's begin by skimming the passage. Remember, paragraph 1 sets the stage, so pay closer attention to it than the others.
Reading strategies
Paragraph 1
Paragraph1. the passage begins with comparing two situations relating to the comet:when it is far from the sun and when it is close to the sun. Whenever a text presents a contrast, it's crucial to organize the ideas accordingly. So, when far from the sun, the comet is a small, dirty ice ball. However, closer to the sun, the ice evaporates, releasing dust and forming a large halo around the ice ball.
When you see the phrase "X is called Y," make sure to note it:
Halo = coma
Ice ball = icy core = nucleus of the comet
The rest of the paragraph goes into detail about how this halo is possible using scientific terms like ultraviolet radiation, low-energy states, and excited atoms. When the passage goes into detail that only a physics major can understand, you should skip it since it's just filler and its purpose is to try to intimidate you
Astronomers now have a fairly good idea of what a comet really is. When it is far from the Sun, it is a very small object only a few kilometers across. It consists mainly of ice (water, methane, ammonia) with bits of dust embedded in it - a kind of dirty ice ball. As it approaches the Sun, radiation from the Sun vaporizes the icy matter and releases some of the dust. This forms a gigantic halo around the ice ball. This halo - called the coma - extends out tens of thousands of kilometers from the icy core, which is the nucleus of the comet. Sunlight reflected off the dust particles makes the coma visible to observers on Earth. Ultraviolet radiation from the Sun breaks down the vapor molecules into their constituents. These components can be excited by absorbing radiation from the Sun. In returning to lower-energy states, the excited atoms and ions emit light, contributing to the luminosity of the coma.
Paragraph 2
Moving on to para 2, There should have been a comma here since “the tail” is the appositive of “one.” that is,
one of its most spectacular parts = the tail.
two types of tails are introduced. the paragraph begins and ends with the dust tail, so we know that para 2 is all about the dust tail
When the comet gets even closer to the Sun, one of its most spectacular parts begins to form, the tail. Actually, there are two kinds of tails: the dust tail and the ion tail. The dust tail is produced by the light from the Sun reflecting off the dust particles in the coma. A photon carries momentum. In bouncing off a dust particle, it imparts a tiny, but perceptible, momentum change to the dust particle, driving it away from the coma. As the comet sweeps along its orbit, it leaves a curving trail of dust behind in its path. This visible dust tail can extend for tens or hundreds of millions of kilometers out from the nucleus. The dust tail is characterized by its gently curving shape and its yellowish color.
para 3
“A different mechanism is responsible for the ion tail” Not surprisingly, we can expect that para 3 is all about the other type of tail, the ion tail.
A different mechanism is responsible for the ion tail. Near the Sun, ultraviolet radiation from the Sun (solar wind) ionizes and excites the atoms in the coma. As the solar wind sweeps through the coma, the high-velocity charged particles of the solar wind interact with the electrically charged excited ions in the coma, driving them away from the head of the comet. In returning to lower-energy states, these excited ions emit photons and form a luminous, bluish-colored tail extending out from the comet directly away from the Sun. Since both kinds of tails are produced by radiation streaming out from the Sun, they extend out from the coma in the general direction away from the Sun. A comet may exhibit several tails of each kind.
Paragraph 4
Paragraph 4 compares the three components of a comet when it is close to the sun: the nucleus, which is a few kilometers in length; the coma, which is hundreds of thousands of kilometers in length; and the tail, which is hundreds of millions of kilometers in length.
Although the nucleus is of the order of a few kilometers in size, the diameter of the coma may be tens or hundreds of thousands of kilometers, the tails typically extend out tens or hundreds of millions of kilometers away from the coma.
Paragraph 5
To understand this paragraph, you'll need to have a basic understanding of the comet's orbit and the Earth's orbit. When the Earth passes through a region that intersects with the comet's orbit, we Earthlings can witness a fleeting streak of light produced by the comet's debris burning up in the Earth's atmosphere.
A comet leaves a trail of matter behind it as it moves through the inner solar system. Some of this debris may get strewn across Earth's orbit around the Sun. When Earth passes through this part of its annual path, it sweeps through the dust trail. The particles enter Earth's atmosphere at high velocity. The air friction can cause one of these bits of matter to produce a brief streak of light as it burns up in the atmosphere.
Paragraph 6
As discussed in previous paragraphs, comets lose matter as they orbit close to the sun. As a result, they will eventually disappear. Based on this fact, astronomers have argued that the lifetimes of comets that we can observe are very much shorter than the age of the solar system. This raises the question of where new comets come from.
Since a comet loses matter on each pass by the Sun, eventually it will be depleted to the point where it is no longer visible. Comets that approach the Sun have finite lifetimes. Given the typical sizes of comets and the typical rates at which they lose matter, astronomers have concluded that the lifetimes of comets with orbits that bring them near enough to the Sun to be seen from Earth are very much shorter than the age of the solar system. Where do the new comets come from to replace the old ones that dissipate and vanish from view?
Para 7
Oort's hypothesis is that there is a giant cloud that surrounds the solar system, which he called the Oort Cloud. I learned about the Oort Cloud from a TOEFL reading passage. This cloud contains the comet nuclei. When a passing-by star perturbs, or disturbs, the cloud, a comet nucleus can be sent hurtling toward the sun.
Dutch astronomer Jan Oort proposed that a giant cloud of matter left over from the formation of the solar system surrounds the Sun and extends out to about 50,000 astronomical units. This cloud contains large chunks of matter like the nuclei of comets. The gravitational influence of a passing star can be sufficient to perturb the orbit of one of these chunks to send it toward the inner solar system and bring it near the Sun.
passage summary:
comets are made of ice and dust,
comets,when they approach the sun, are composed of nuclei, comas and tails
comets leave trash, and the trash can enter the earth’s atmosphere when the earth passes through this part. when this happens a brief streak of light is created
since comtes lost matter, they eventually disappear. so, the question is where do the new comets come from?
from the OOrd cloud
Problem-solving strategies
Q1: reference question
1.Which part of a comet is described in the passage as a "dirty ice ball " ?
A.The nucleus
B.The coma
C.The dust tail
D.The ion tail
Analysis
The dirty ice ball approaches the sun → releases the dust → forms a halo around the ice ball.
halo = coma
ice core = nucleus = dirty ice ball
Answer：A
Q2. Information question
Select the TWO answer choices from paragraph 1 that describe changes that occur as a comet approaches the Sun. To receive credit, you must select TWO answers.
A.Water, methane, and ammonia condense into a core.
B.The icy content of the comet begins to vaporize
C.The comet' s halo decreases in size
D.Dust particles and vapor form a coma
Analysis
The dirty ice ball approaches the sun → the ice evaporates → the dust released → halo formed around the ice ball.
Answer: BD
Q3: vocab question: root word “lumin”
3.The word "luminosity" in the passage is closest in meaning to
A.immensity
B.development
C.display
D.brilliance
Analysis
The word "lumin" originates from the Latin word "lumen," meaning "light." It is the root word for several English words that are related to light, brightness, and knowledge. Here are a few examples:
Illuminate (into the light = To provide light; to make something clear or understandable.)
Luminous (a lot of light = shining brightly.)
Luminescence (some quality relating to brightness).
Luminosity (The degree of brightness)
Luminary (something that is so bright → a distinguished person for her knowledge)
So look for an option that relates to light or brightness, which is D.
Answer：D
Q4 Vocab question: prefix + root of “impart”
4.The word "imparts" in the passage is closest in meaning to
A.shows
B.gives
C.confirms
D.maintains
Analysis
Impart = into parts so that you can give a part to others. used for abstract things, especially knowledge.
A teacher’s job is to impart knowledge to her students.
Q5. Negative info question: an elimination strategy
5.According to paragraphs 2 and 3, all of the following statements about comet tails are true EXCEPT:
A.Ion tails are created by ultraviolet radiation
B.Photons are active in creating both ion tails and dust tails.
C.Dust tails follow in the path of a comet.
D.Ion tails have a curved shape and yellowish color.
Analysis
Negative information questions are not difficult in themselves, but they require more time than other questions because you have to carefully examine each option. Therefore, I'd like to share a useful tip that can help you save time. Upon analyzing various TOEFL questions, I've observed that the correct answer choices often avoid technical jargon that may be challenging to comprehend. In other words, the correct options are typically those that convey easily understandable meanings. This strategy can be particularly effective in saving time when dealing with negative information questions.
A. I'm not familiar with the term "ultraviolet radiation," so option A appears too technical.
B. The term "photons" seems technical as well, so I'll eliminate option B.
C. I comprehend the meaning of option C, so I'll proceed to check its validity. We know from paragraph 2 that the dust tail "leaves a curving trail of dust behind in its path." This implies that the tail follows the path. Consequently, option C is correct.
D. Option D is easy to understand, so let's examine the text for information that supports or refutes its claim. The text states that the dust tail is characterized by its "gently curving shape and its yellowish color." This suggests that option D is incorrect.
Answer: D
Q6. Inference question: Eliminate improbable ones first
According to paragraph 3, the tails of a comet
A.flow in the same direction as the radiation that produces them
B.become straighter as the comet moves away from the Sun
C.are pulled toward the Sun
D.can become detached from the comet head if the solar winds are strong enough
Analysis
We've already learned some information about comet tails, which we can use to eliminate some clearly incorrect options.
A: We don't know for sure, so keep it for now.
B: We know that B is false. Remember that the dust tail is curved?
C: We don't know for sure, so keep C. Both A and C talk about direction, so we can expect that the correct answer must be related to the direction of the comet's tails.
D: D can be eliminated since the tail getting detached was never mentioned.
So, the correct answer must be either A or C. Let's go back to the passage that discusses the direction of the tails.
According to the passage, 'Since both kinds of tails are produced by radiation streaming out from the Sun, they extend out from the coma in the general direction away from the Sun.' So, C is false. Therefore, the answer must be A. The tails are produced by the sun's radiation, so they should flow in the same direction as the radiation.
Answer：A
Q7. Paraphrase question: comparison of items
7.Which of the sentences below best expresses the essential information in the highlighted sentence in the passage?Incorrect choices change the meaning in important ways or leave out essential information.
A.The diameter of a coma is usually larger than the tails that extend away from it while the nucleus is much smaller.
B.The diameters of the nucleus, coma, and tail of a comet exhibit minor differences in size.
C.The nucleus is reduced in size, while the coma and tails extend far into space
D.Comet tails are much larger than the coma, which is much larger than the nucleus
Analysis
We analyzed in para 4, and the answer is D.
Answer：D
Q8: Vocab question: common word
8.The word "strewn" in the passage is closest in meaning to
A.combined
B.damaged
C.observed
D.scattered
Analysis
“Strewn” means things being all over the place. So scattered is a synonym.
Answer：D
Q 9: Information Question: explicit info
9.According to paragraph 5, what happens when Earth passes through the dust trail of a comet?
A.Dust particles burn up in Earth' s atmosphere.
B.The comet' s orbit is changed.
C.The dust trail is completely destroyed
D.The comet' s tails change direction.
Analysis
The information for this question is explicitly stated.
Answer：A
Q10. Inference question: Eliminate definitely wrong ones first
10.What does paragraph 6 imply about comets that are visible from Earth?
A.The visible comets grow brighter as they grow older
B.The comets that are visible from Earth today have not been orbiting close to the Sun throughout the history of the solar system
C.There were fewer visible comets during the early history of the solar system than there are today.
D.The average lifetime of the visible comets is decreasing.
Analysis
From paragraphs 6 and 7, we know these:
The comets that orbit the sun has much shorter life than the solar system
Comets come from the Oort Cloud when they were disturbed
A should be false. As comets grow older, they will lose material, becoming duller.
B the comets that we can see have a short lifespan, which implies that they have not been orbiting close to the Sun throughout the history of the solar system. So B can be entailed.
C and D cannot be determined from the passage.
Answer：B
Q11. Organization question: relationship between two paragraphs
Why does the author end paragraph 6 with a question?
A.To indicate that certain information about comets is unknown
B.To introduce a topic that will be clarified in the next paragraph
C.To propose an area that requires further research
D.To challenge theories that were presented earlier in the passage
Analysis
A is true, but the next paragraph, 7, provides an answer to the question. So. A is not true.
B is the way it is organized.
C is wrong for the same reason as mentioned in A.
D is not close.
answer：B
Q 12. Information question
12.According to paragraph 7, how did astronomerJan Oort contribute to our understanding of comets?
A.He theorized that comets form when passing stars push chunks of debris from the outer to the inner solar system
B.He proposed a way of comparing comets in our own solar system with those that orbit other stars.
C.He explained that the lifetime of a comet depends on its distance from the Sun at the time the solar system was formed.
D.He proved that old comets do not really disappear; they just move beyond the limits or the solar system.
Analysis
Oort explained the origin of comets.
A describes the origin of comets
B and C are not mentioned.
D is wrong because of the word “prove.”
Answer: A
Q13. Sentence insertion question: “this” as clue
13.Look at the four squares[■]that indicate where the following sentence could be added to the passage. This streaking phenomenon is called a meteor or sometimes a falling star or shooting star. Where would the sentence best fit? Click on a square [■] to add the sentence to the passage.
This streaking phenomenon is called a meteor or sometimes a falling star or shooting star.
Analysis:
The target sentence should come after some streaking phenomenon. C contains the word streaks, so the target should come after C.
Answer：D
Q14 Summary question: pay attention to the ISS
14.Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage This question is worth 2 points. Drag your answer choices to the spaces where they belong. To remove an answer choice, click on it. Astronomers have acquired much information about the composition of comets and the ways comets change as they move through the solar system.
A.Ices and dust particles compose the nucleus of a comet.
B.The type of tail exhibited by a comet depends on its proximity to the Sun
C.The solar system contains a limited number of comets
D.A comet produces tails and a coma as it approaches the Sun.
E.The coma of a comet is typically larger than the tail of a comet
F.Comets lose matter each time they pass by the Sun, until they eventually disappear.
Analysis
This is the introductory summary sentence: Astronomers have acquired much information about the composition of comets and the ways comets change as they move through the solar system.
So the correct options must talk about the compositions and changes of the comet.
A talks about the composition of the comet, so keep A.
B: The types do not depend on the proximity to the Sun. So B is out.
C: We don't know for sure, and even if they are true, they are not essential information.
D talks about changes of the comet, so D should be included.
E is false.
F talks about another change of the comet, so we should keep it."
Answer: ADF