The Properties of Spiral Galaxies, Including Our Own

Question:  Me and the rest of our fifth grade class is learning about galaxies, but I have a couple questions. Why is the middle of a spiral galaxy bigger than the arms? How fast is our Galaxy moving, is it even moving at all? Do you think that there is life on other galaxies?  — Anthony

Answer:  Just like people, galaxies come in a lot of different shapes and sizes.  As you probably already know, there are galaxies that look round, called “elliptical galaxies”, and galaxies that look more like a spiral, called “spiral galaxies”.  For the spiral galaxies there are some that have small centers (or “nuclei”) and large/wide arms, while others have the opposite: big nuclei and rather small arms.  The NOAO Spiral Galaxy image gallery gives you a good idea as to the range of different sub-types of spiral galaxy.

As for your second question about the rotation speed of our galaxy, we have measured that speed to be about 270 kilometers per second (or about 168 miles per second).  Finally, is there life in other galaxies?  Well, there are approximately a hundred-billion stars in our galaxy, and approximately a hundred-billion galaxies in the universe.  It would be difficult to believe that our single star, which we call the Sun, would be the only star in the universe that possesses life.

Jeff Mangum

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