Spinning Around Earth
Right now, hundreds of machines are zooming around Earth at 17,000 miles per hour — faster than a speeding bullet times 20! You cannot see them with your eyes, but they help your family find directions, watch TV, and know when a storm is coming. These amazing machines are called satellites, and they live in outer space.
What You'll Learn
After this lesson you will be able to: • Explain what a satellite is and why it stays up in space • Name three things that satellites help us do every day • Understand the difference between natural and human-made satellites • Explain how GPS uses satellites to show you where you are
What Is a Satellite?
A satellite is any object that travels in a circle — called an orbit — around a bigger object. The Moon is Earth's natural satellite; it has been orbiting Earth for about 4.5 billion years! But humans have also launched thousands of artificial (human-made) satellites. The very first one was called Sputnik 1. It was launched by the Soviet Union on October 4, 1957, and it was only about the size of a beach ball. Today there are more than 8,000 working satellites circling Earth.
Why Do Satellites Stay Up?
You might wonder: why do satellites not fall down? They actually ARE falling — but they are also moving sideways so fast that they keep missing Earth! Imagine throwing a ball super fast off a very tall mountain. Gravity pulls it down, but if you threw it fast enough, Earth's surface would curve away just as fast as the ball falls. That is exactly what a satellite does. It is in a constant free fall around Earth, never hitting the ground because it is moving so fast sideways.
GPS satellites orbit about 12,500 miles above Earth — that is about 50 times higher than a passenger airplane flies! It takes each GPS satellite about 12 hours to complete one full circle around our planet.
How GPS Tells You Where You Are
GPS stands for Global Positioning System. It uses 24 satellites spread evenly around Earth. Each satellite constantly sends out a radio signal like a lighthouse flashing in space. Your phone or GPS device listens to signals from at least 4 satellites at once. Because radio signals travel at the speed of light, your device can measure the tiny differences in how long each signal takes to arrive. By doing math with those time differences, it can figure out exactly where you are on Earth — sometimes to within 3 feet!
Flashcards — click each card to reveal the answer
Why does a satellite not fall down to Earth?
Match each satellite term with its meaning.
Terms
Definitions
Drag terms onto their definitions, or click a term then click a definition to match.
How many satellites does GPS need to pinpoint your exact location?
Satellite Orbit Model
1. Find an open outdoor space or a large room. 2. Stand in the middle — you are Earth! 3. Ask a friend or family member to walk in a big circle around you without stopping — they are the satellite! 4. Try this: have the satellite walk faster and faster. Notice how they lean inward to keep the circle tight? That lean represents gravity pulling them toward Earth. 5. Draw your model: label Earth (you), the satellite (your partner), and the orbit path (the circle). Add an arrow showing the direction of travel. 6. Write one thing the satellite helps people on Earth do every day.
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