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You and I have talked a lot about space, haven't we? We learned about stars, we found out all about comets and asteroids, and we can even name all eight of the planets in our solar system. But have you ever thought about what's beyond our solar system? The Sun is just a star after all, and it, along with us and all the other planets, aren't just floating around in space all by ourselves. Oh, no. Our solar system is part of something much, much bigger, a galaxy.

A galaxy is a huge bunch of stars that are clustered together in space, and the galaxy that our solar system is part is called the Milky Way. The Milky Way is full of stars. How many? Well, do you know how much a thousand is? A thousand looks like this, and if you take a thousand and multiple it by a thousand and multiple it by a thousand again, that number is a billion. And, there are billions of stars just in the Milky Way alone. In fact, there are so many stars in the Milky Way that we still don't know exactly how many there are, but scientist think that many of the other stars in our galaxy probably have planets of their own.

And the Milky Way isn't the only galaxy. Astronomers who study deep, distant space have found other galaxies, too. More than you could count. To organize and study all of these galaxies, astronomers usually group them into three main types, depending on their shape. There are spiral galaxies, elliptical galaxies, and irregular galaxies.

Spiral galaxies are in the shape of a pinwheel. They have that shape, because stars in a spiral galaxy are clumped into lines that curl outward. These lines are called spiral arms. And, the galaxy that you and I are in right now, the Milky Way galaxy, is a spiral galaxy. Now, some spiral galaxies are just flat, like a pancake, but other spirals, including our own Milky Way, have a large bulge in the middle that's made up of a big bunch of stars. The stars in the bulge are usually older stars, while younger stars are often found on the outer spiral arms of the galaxy. Astronomers even know where our star, the Sun, is in the Milky Way. If you were way, way out in space, floating above our galaxy and looked down at it, you'd find the Sun right about here, near the middle of one of the spiral arms.

Now, another common kind of galaxy is called an elliptical galaxy. Elliptical galaxies are shaped like an ellipse or an egg shape, and, instead of being flat with a bulge in the middle, these galaxies are all bulge. They tend to have mostly older stars in them, and stars in an elliptical galaxy are really close together, which makes the middle of the galaxy look like one giant, bright star.

The last common type of galaxy is an irregular galaxy. Irregular means not regular, and these kinds of galaxies don't have a definite, regular shape. Instead, these cluster of stars can take all kinds of different shapes, like this or this or even this.

There are tons of other galaxies out there to learn about, and scientists are discovering new ones all the time. So the next time you're out at night gazing at the sky, remember that you and the Earth and the whole solar system are part of something bigger, a galaxy.

Thanks for joining us today. If you have a question for us about space, or the Earth, or anything at all, just let us know by getting help from a grownup and leaving a comment below. Or, send us an email to and we'll see you next time.