Dear Erin,

If you are anything like me, you probably like watching for shooting stars in the night sky. A shooting star, or a meteor, is usually a small rock that falls into Earth’s atmosphere.

When I went to visit my friend Michael Allen, a senior instructor of astronomy and physics at Washington State University, he told me a lot of shooting stars are no bigger than a pencil eraser.

“The earth is going to pass a random pebble once in a while and that will make a streak in the sky,” he said.

You might be wondering how such a small rock can create such a bright streak of light. If you’ve ever rubbed your hands together, you may know that friction is what helps them warm up.

When a small rock is falling into Earth’s atmosphere, it falls super-fast. Depending on the meteor, it can travel anywhere from 36,000 feet to 236,220 feet in a single second. As it falls, there is a lot of friction between the air and the rock. With all that friction, the rock starts to get really hot.

It is this friction that will help melt part of the rock. If the rock is small enough, it will evaporate, leaving behind a trail of hot gasses—and that’s the shooting star that you see streaking across the night sky.

Every now and then, we can see lots of shooting stars in the sky at the same time. When we see a meteor shower, we are seeing the little bits of a comet that has worked its way through the solar system. These meteor showers happen about a dozen times over the year and most last just a couple of hours.

When the icy comet intersects with Earth’s orbit, it gets heated up by the sun, and can break up into lots of smaller pieces of rock that can fall into Earth’s atmosphere. Meteors are rich in glassy or sandy materials, like quartz.

If a rock makes it from outer space to the surface of earth, we call it a meteorite. Allen also told me it’s really hard to know just by looking at a rock if it is from Earth or if it is something extraterrestrial.

If we really wanted to find out if a rock was a meteorite, we would need to look very closely at its atoms and its structure in a lab.

When we take a look at what makes up objects in space, we can learn quite a lot. By the way, unlike meteors, which are a solid, actual stars are really big exploding balls of gas. They are mostly made up of gases called hydrogen and helium.

The next time you look up to the vast night sky, remember that even the tiniest specks of dust and rock can light up the darkness—and that interstellar dust is falling around us all the time.

Dr. Universe

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