Short answer: A meteor shower happens when Earth passes through a trail of dust left behind by a comet. Most meteors are no bigger than a grain of rice and burn up in the atmosphere. Because Earth crosses the same trail at the same point in its orbit, showers return at the same time each year.
We’ve all seen a meteor shower, but do you understand the physics behind it? This post was written for the “unicorn” meteor shower of November 2019, the alpha Monocerotids, named for the constellation Monoceros, the unicorn.
Key points
- Dust, not boulders: Most meteors are dust no larger than a grain of rice burning up in the air.
- Comet trails: The dust is debris spread along a comet’s orbit around the sun.
- Same time every year: Earth crosses the debris trail at the same point in its orbit each year.
- Earth’s speed: Each streak is partly Earth’s own motion, about 67,000 miles per hour.
What is the physics of a meteor shower?
A giant rock hurtling through space? Nope. It’s actually dust burning up in the atmosphere. Most meteors are no larger than a grain of rice.
The dust comes from a comet. As a comet nears the sun, it sheds dust and rock along its path, leaving a trail of debris spread along its orbit.
When we see a meteor shower, Earth is passing through that dust trail on its orbit around the sun. That’s why showers occur at the same time each year.
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What are you really seeing when a meteor streaks across the sky?
When you see a meteor streak across the sky, you are seeing the dust and the Earth collide. A big part of that speed is the motion of the Earth itself, plowing through the dust on its journey around the sun.
So when you see a meteor, think of it as a way of experiencing the enormous speed of the Earth orbiting the sun: about 67,000 miles per hour.
Tutor tip: Turn the next meteor shower into a physics lesson: ask your student how far Earth travels in one minute at 67,000 miles per hour (about 1,100 miles). For more ways to encourage a young stargazer, see our astronomy guide for beginners.
Tutor-written guide · PDF
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Frequently asked questions
What causes a meteor shower?
A meteor shower happens when Earth passes through a trail of dust and rock left behind by a comet. The small pieces burn up as they hit Earth’s atmosphere, creating streaks of light.
Why do meteor showers happen at the same time every year?
The comet’s debris is spread along its orbit, and Earth’s orbit crosses that path at the same point each year. So the same shower returns on roughly the same dates annually.
How fast does Earth travel around the sun?
Earth orbits the sun at about 67,000 miles per hour. Part of the speed of every meteor you see comes from Earth’s own motion as it plows through the debris trail.
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