Scaling the Sun Earth Moon System

Once students understand how all matter is formed from chemical reactions between atoms, they compare the relative properties of the Sun, Moon, and Earth. In this lesson, students create a scale model to look at the size, distance, and gravity of these three bodies in our solar system, analyzing how these properties influence their interactions.

• Earth is one small part of a much larger universe and is one of eight known planets in the solar system. 
• In order to understand the relationship between different objects in the universe, such as the size of a planet relative to another planet, or the distance of different planets from the sun, scientists use scale—the size, extent, or importance of something relative to something else. 
• Scale comparisons use everyday objects to help us understand the different sizes of the planets in comparison to one another. 
• The masses of the different objects of the solar system are very different, so scientists use scale to help understand how these objects relate to one another in terms of their mass.
• The Sun is the most massive object in our solar system. This means that it is made up of more matter than Earth is. The Sun is so massive that more than one million Earths could fit inside it. 
• Extremely large distances separate Earth from other planets and the sun, even though the Sun is the closest star to Earth. These distances explain why our sun appears smaller than Earth in the sky, but also larger and brighter than any other star. 
• The mass of the sun and its closeness to Earth (and the other planets in the solar system) cause the planets to orbit it. 
• Gravity’s attractive pull is what causes motion in the solar system, and its strength depends on the mass of the interacting objects and their distance from one another. 
  
  

• How does Earth stay in our solar system?
• Why are the Sun, planets, and moons all examples of matter?
• How would you describe the properties of the Sun and Earth?
• Why is it useful to use scale comparisons to describe the mass of the planets relative to each other and the Sun?
• How do we know that the Sun is the closest star to Earth?
• Why does the Sun appear smaller than Earth in the sky, even though it is so much larger than Earth?
• Why does Earth orbit the Sun?
• Why does the Moon orbit Earth if the Sun is so much more massive than Earth?
  
  

Misconception: Earth does not move.

Fact: Earth is in constant motion. It is continually orbiting the sun, making one complete orbit around the sun in about one Earth year. At the same time, Earth rotates around its axis, causing day and night.

Misconception: The moon changes its size throughout the month.

Fact: The moon stays the same size. What changes is how much of the moon we can see from Earth because of the moon’s position relative to the sun as the moon orbits Earth.

Gravity : a force of attraction between all matter

Mass : a measure of the amount of matter that makes up an object; measured in grams (g)

Scale :  the size, extent, or importance (magnitude) of something relative to something else

Solar System :  a collection of planets and other objects that orbit a star

Weight :  the gravitational force exerted on an object by a planet or moon; measured in newtons (N)

Looking Back in Time

The Hubble Space Telescope allows scientists to look back in time. This means they can study the history of the universe. This is possible because when you look at the stars in the night sky, you are seeing light that is thousands or millions of years old. This light has traveled billions of miles through space to reach your eyes.

The farther away an object is, the longer its light takes to reach you. When you look at an object across the room, you actually see it as it was a few billionths of a second ago. Stars are so far away that it takes a very long time for their light to reach us.

For example, the Hubble Space Telescope has taken pictures of a large cluster of stars that is 100 million light years away. The distant stars are so far away that the images are actually from 100 million years ago. At the time that light left those stars, dinosaurs still roamed Earth.

Scaling the Universe

The universe is full of mostly empty space. Millions of miles separate Earth from other objects in the universe. The universe is so immense that when scientists talk about distances, they often use scale models. Scale models are useful for scientists who want to understand how the various parts of the universe interact. For example, scientists can use a scale model to observe the different parts that make up the universe.

Earth is part of the Milky Way Galaxy. A galaxy is a large cluster of stars. The Milky Way Galaxy is shaped like a thick pancake. It contains billions of stars. There are hundreds of billions of galaxies in the universe.

Scaling Distance

Earth is part of a solar system in the Milky Way Galaxy. A solar system is a collection of planets and other objects that orbit a star. A planet is a body that orbits (travels in a circle around) the sun, is massive enough for its own gravity to make it round, and has cleared out smaller objects around its orbit.

The Sun is the center of our solar system. The sun is a star orbited by planets. There are eight known planets in our solar system.

Our sun is much closer to Earth than any other star. In Earth terms, however, it is still very far away. It is 150 million kilometers (93 million miles) away from Earth. At this distance, it takes sunlight eight minutes to travel from the Sun’s surface to Earth. Neptune, the farthest planet from the sun, is much farther than Earth. It is 4.5 billion kilometers (2.8 billion miles) from the sun.

For the hands-on activity of this lesson, students create a scale model of the Sun Earth Moon system to observe the relative properties (size, distance, and gravity) of these bodies in the solar system. Students use the model to analyze how the relative properties determine the place and motion of each body in the solar system.