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Scale of the Solar System — Reading Comprehension

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MS-ESS1-3

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This passage, aligned to NGSS standard MS-ESS1-3, helps middle school students grasp the immense scale of the solar system. It covers how scientists use models and analogies, such as comparing the Sun to a basketball and planets to different-sized objects, to visualize distances that are otherwise hard to imagine. Students learn why most of the solar system is empty space, how light and radio signals travel between planets, and the technological and communication challenges this creates. The passage connects these concepts to real-world exploration, such as the Voyager 1 mission and the nearest star beyond our solar system. Activities include comprehension questions, writing prompts, and graphic organizers to support understanding. Audio integration supports diverse learning needs. Keywords: solar system, scale, distance, NGSS, science education, light year, AU.

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"Solar system scale" by Lunar and Planetary Laboratory /
Source: Wikimedia Commons (Public domain).

The solar system is the collection of the Sun, eight planets, their moons, and many smaller objects, all bound together by gravity. Scientists study the solar system to understand why the planets move as they do and how they interact with each other. One major challenge in studying the solar system is grasping its vast scale. Most of the space between planets is empty, and the distances are so large that even light takes minutes or hours to travel from one place to another.

Understanding the Immense Distances

To better understand these distances, astronomers use models and analogies. For example, if the Sun were the size of a basketball, Mercury would be a peppercorn about 15 meters away, Earth would be another peppercorn 38 meters from the Sun, and Jupiter would be a large grapefruit 200 meters away. Neptune, the most distant planet, would be a walnut 1.2 kilometers from the Sun. The distances between planets are often measured in astronomical units (AU), where 1 AU is the distance from Earth to the Sun, about 150 million kilometers. Mercury is only 0.4 AU away, while Neptune is 30 AU from the Sun. This shows that most of the solar system is empty space, with planets orbiting at great distances from each other and from the Sun.

Light, Communication, and Space Exploration

Light travels very fast—about 300,000 kilometers per second—but even at that speed, it takes 8 minutes to reach Earth from the Sun and 4 hours to reach Neptune. When scientists communicate with spacecraft, such as the Mars rover, they must wait 4 to 24 minutes for messages to travel between Earth and Mars, depending on their positions. The Voyager 1 spacecraft, launched in 1977, is now over 23 billion kilometers from Earth, about 156 AU. A radio signal from Earth takes over 21 hours just to reach Voyager 1. Yet, Voyager 1 is still only about 0.002 light-years away. In comparison, the nearest star, Proxima Centauri, is 4.2 light-years, or about 268,000 AU from the Sun. This demonstrates just how tiny our solar system is compared to the galaxy.

Why Scale Models Matter

Because it's impossible to build a model that shows both the size of planets and the distances between them accurately, scientists use scale models to help people picture the solar system. These models help us understand why space exploration is so difficult—spacecraft must travel enormous distances through mostly empty space. Understanding the scale of the solar system also helps scientists plan missions, predict planetary movements, and develop new technology for communication and exploration. The study of the solar system connects to larger scientific principles, such as gravity and the nature of space and time.

Understanding the scale of the solar system reveals the challenges faced by scientists and engineers and highlights our place in the universe. The vastness of space encourages new questions about how we might explore further in the future.

Interesting Fact: If Voyager 1 kept traveling at its current speed, it would still take over 70,000 years to reach the nearest star, Proxima Centauri!

What is one main challenge scientists face when studying the solar system?

Understanding the vast distances between objectsCounting all the moons in the galaxyFinding new elements on EarthMeasuring rainfall on Jupiter

In a scale model where the Sun is a basketball, how far away would Neptune be?

15 meters1.2 kilometers38 meters200 meters

What is an astronomical unit (AU)?

The distance from Earth to the MoonThe average distance from Earth to the SunThe width of JupiterThe speed of light

How long does it take for light to travel from the Sun to Earth?

8 minutes1 hour21 hours4 hours

What does the passage say about Voyager 1?

It is already outside the Milky WayIt is still only a tiny fraction of a light-year from EarthIt takes 8 minutes to send it a messageIt is the closest planet to the Sun

What is the purpose of using scale models in studying the solar system?

To show both planet sizes and distances perfectlyTo help visualize the vast distances and empty spaceTo shrink the real planets for easier studyTo find new moons around Neptune

Why do scientists have to wait for messages when communicating with space probes?

Because signals travel slowly through Earth's airBecause of the huge distances signals must crossBecause planets block all signalsBecause probes only receive messages at night

If the Sun is a basketball in a model, what object represents Earth?

A walnutA peppercornA grapefruitA marble

True or False: The passage says that most of the solar system is filled with empty space.

TrueFalse

True or False: The passage claims that Proxima Centauri is less than 10 AU from the Sun.

TrueFalse