Today’s Wonder of the Day was inspired by Chuck from ID. Chuck Wonders, “Why do they call it the Milky Way? ” Thanks for WONDERing with us, Chuck!
Where do you live? If asked that question, you might respond with the name of the street you live on. Or you might tell someone what town you're from. If you're on vacation, you might even respond with your state or country.
But what if aliens asked you? If you told them Earth, they might have no idea what or where Earth is. You might have to tell them what galaxy you live in. Have you ever thought of yourself as the resident of a galaxy? Well, you are! And it's called the Milky Way.
A galaxy is a huge group of stars that are bound together by gravity. How huge? Consider this: our star — the Sun — is just one of approximately 200 billion stars in the Milky Way! Just about everything we can see in the sky is part of the Milky Way.
The Milky Way is a barred spiral galaxy. This means it is like a thin disk with arms that radiate outward in a spiral shape. Our solar system can be found on the outer edge of the Milky Way on one of the spiral arms.
The Sun is about 25,000 light years from the center of the Milky Way. Overall, the Milky Way is between 80,000-120,000 light years wide, but only about 7,000 light years thick.
It's hard to understand these measurements, so you can think of the size of the Milky Way in this way: if you reduced it to the size of a football field, our solar system would be about the size of a grain of sand and located at one of the outer edges.
Our solar system orbits around the Milky Way at the rate of about 155 miles per second. That's fast! But the Milky Way is so huge that it still takes our solar system about 200-250 million years to orbit once around the Milky Way!
You may see pictures of the Milky Way from time to time. These are not actual photographs, because we've never sent a spaceship outside of the Milky Way. However, special telescopes allow astronomers to know a lot about our galaxy. Its hazy, “milky" appearance gave rise to its name.
As big as the Milky Way is, it's only one of several galaxies in a group of galaxies that astronomers call the Local Group. To make you feel even smaller, astronomer Edwin Hubble showed in the 1920s that the Milky Way is only one of about 200 billion galaxies in the universe!
And, as galaxies go, the Milky Way isn't nearly the largest. Astronomers believe the nearby Andromeda Galaxy contains as many as one trillion stars!