TOEFL Complete the Words : Astronomy (Intermediate)

Complete passage

Each year, certain nights offer spectacular displays of meteor showers, events caused by streams of debris left behind by comets or, in some cases, asteroids. As Earth passes through these particle trails, small fragments enter the atmosphere at high speeds and vaporize dueto intense friction, producing bright streaks of light in the sky. The apparent increase in activity occurs because the particles originate from a common stream in space, causing the meteors to seem to radiate from a single point. Astronomers use careful observation and long-term data collection to predict the timing and intensity of major meteor showers with considerable accuracy.

Scenarios describing a meteor, asteroid, or space debris entering Earth’s atmosphere and vaporizing appear frequently in TOEFL astronomy topic. In simpler terms, this means that the object burns up. However, this casual expression is rarely used in TOEFL, which tend to prefer more formal and technical wording.

The term debris refers to fragmented objects in space. It is commonly understood as “space junk” or “space garbage,” but TOEFL passages typically use the more neutral and academic term “debris.”

In addition, although it is not limited to astronomy-related topics, the word “observation” is strongly preferred in TOEFL passages. Instead of casual alternatives such as looking at or watching, TOEFL texts consistently use more academic terms like observation to describe the act of examining phenomena.

Complete passage

Differences among the planets of our solar system reflect variations in composition, distance from the Sun, and atmospheric conditions. Mercury, located closest to the Sun, experiences extreme temperature shifts because it lacks a substantial atmosphere. Venus, by contrast, is surrounded by a dense atmosphere rich in carbon dioxide, resulting in an intense greenhouse effect. Mars shows evidence of past water activity, suggesting that its climate was once more habitable for life. Beyond the asteroid belt, Jupiter and Saturn differ fundamentally from the inner planets, as they are composed primarily of gases and possess numerous moons and ring systems. Together, these contrasts illustrate how planetary characteristics are shaped by both formation history and environmental factors.

Astronomy-related passages and listening tasks become much easier to follow once you understand some basic terminology. One important group of terms is planet names. In addition to Earth, the following five planets are commonly mentioned in TOEFL materials:

• Mars: Shows evidence that liquid water existed in the past.
• Mercury: The planet closest to the Sun, known for extreme temperature differences between day and night.
• Jupiter: The largest planet in the solar system, composed mainly of gas.
• Venus: Covered by a thick, carbon-dioxide-rich atmosphere and the hottest planet in the solar system.
• Saturn: A gas giant surrounded by prominent ring systems and many moons.

Another important word frequently used in astronomy contexts is “habitable.” This term refers to whether an environment can support life.

Complete passage

Red dwarfs are the most common type of star in the Milky Way, yet they are often difficult to observe due to their low luminosity. Compared to larger stars, red dwarfs burn fuel far more slowly, allowing them to remain stable for trillions of years. This extraordinary longevity has led astronomers to consider the possibility that planets orbiting red dwarfs could sustain life. However, such stars are also known for frequent stellar flares, which may substantially affect the atmospheres of nearby planets and pose challenges for long-term habitability.

Details about red dwarfs are a common topic in TOEFL passages and lectures. Because their characteristics are not immediately clear from the name alone, many test takers feel uneasy when they encounter this topic.

The solution is simple, though. Once you understand the basic properties of red dwarfs, the topic becomes much easier to handle. With this background knowledge, you can quickly picture what is being described in a passage or lecture and focus on answering the questions.

Below is the essential information you need to know about red dwarfs for the TOEFL.

Red dwarfs are small, cool stars with relatively low mass and luminosity. Remember that they are a type of star. They are the most common type of star in the Milky Way galaxy, yet they are difficult to observe with the naked eye because they emit very little visible light.

One defining characteristic of red dwarfs is their extremely slow rate of nuclear fusion. Because they consume hydrogen fuel efficiently, red dwarfs can remain stable for trillions of years, far longer than stars like the Sun. This makes them the longest-living stars known.

It is called red dwarfs because they emit red light because of their relatively low surface temperature causes them to emit more red light than blue or white light, and the fact that compared to stars like the sun, they are much smaller and less massive.

They are called red dwarfs for two main reasons. First, their relatively low surface temperature causes them to emit more red light than blue or white light. Second, compared with stars like the Sun, they are much smaller and less massive, which explains the term dwarf.

Complete passage

White dwarfs represent the final evolutionary stage of many medium-sized stars after they have exhausted their nuclear fuel. Following the collapse of the stellar core, the remaining material is compressed into an extremely dense object no larger than Earth. Despite their small size, white dwarfs retain enormous mass, resulting in gravitational forces strong enough to prevent further collapse. Unlike active stars, white dwarfs no longer generate energy through fusion; instead, they gradually cool as stored thermal energy is released into space. Over time, their brightness diminishes, making them increasingly difficult to detect. The study of white dwarfs therefore provides astronomers with valuable insight into stellar aging and the long-term evolution of galaxies.

Another common type of star that appears in TOEFL materials is the white dwarf. Although white dwarfs share the word dwarf with red dwarfs, they represent completely different stages of stellar evolution.

Simply put, a white dwarf is a star that has already used up its nuclear fuel and can no longer produce energy through nuclear fusion. In other words, it represents a late stage of stellar evolution.

Despite the lack of ongoing fusion, white dwarfs remain extremely hot for a very long time. This is mainly because they are extraordinarily dense. A white dwarf is roughly the size of Earth but contains a mass comparable to that of the Sun. In addition, its relatively small surface area limits how quickly heat can escape. As a result, it takes an enormous amount of time for a white dwarf to cool.

Because of their high surface temperature, white dwarfs often emit blue or white light, which indicates intense heat. However, since they no longer generate new energy, they are destined to gradually cool and fade over time.

An analogy may help clarify the difference. You can think of red dwarfs as engines running slowly with an abundant fuel supply, while white dwarfs are engines that have already consumed all their fuel. Both engines are hot, but the white dwarf remains hot only because of stored energy, not because it is still producing new power.