The Milky Way, Our Home

By Tony Helies • Illustrated by Tom Powers

	Scientists think our galaxy looks a lot like galaxy M 100, shown above.

We live in a pinwheel of stars.
On dark, clear, moonless nights, far from city lights, you can see a hazy band of light stretching across the sky. If you look at this glow with binoculars, you will see that it is light from thousands of stars. These stars, and all the stars you see in the night sky, are part of a huge system of stars called the Milky Way galaxy.

Our Sun is a star in the Milky Way, too. So when you look at the sky from Earth, you are looking at the Milky Way from the inside. If you could view our galaxy from far away, it would look very different.

Imagine that you are a space traveler in a rocket ship far from our galaxy. From your spaceship window, the Milky Way looks like a glowing pinwheel. In the center of the pinwheel, you see a bright yellow bulge. Spiraling out from the center, the arms of the pinwheel look light blue against the darkness of space.

Old Stars, New Stars
As you rocket closer, you see that the Milky Way is made up of stars and clouds of glowing gas. The center of the galaxy is a mass of old yellow, orange, and red stars, formed when our galaxy was young. They have been burning for a long time. In the outer spiral arms of the galaxy, new stars are being formed. The brightest of these young stars are very hot and, like a really hot flame, they give off a blue light.

Our Sun is a yellow, middle-aged star about halfway out from the galactic center in one of these brilliant spiral arms. But you probably wouldn’t even be able to pick out our Sun in the blaze of starlight coming from the galaxy. That dazzling light comes from more than 200 billion stars!

As your spaceship finally reaches the outer edges of the galaxy, you may worry that you will crash into some of those stars. But the stars are spread across a lot of space. The Milky Way is so big that it takes light more than 100,000 years to travel from one side of the pinwheel to the other. If you built a scale model of the Milky Way with each star the size of a grain of salt, your model would have to be twenty-five times wider that Earth. In this model, the grains of salt in the spiral arms would be seven miles apart. So even though our galaxy is enormous, it is mostly empty space.

Speeding Stars
The Milky Way not only looks like a pinwheel, it spins like one, too. All the stars are speeding around the galactic center. Our Sun is traveling at 140 miles per second. That’s three hundred times faster than a speeding bullet. The Earth moves with the Sun in its rapid journey around the galaxy. We don’t feel as if we are moving for the same reason airline passengers feel no motion when their plane is cruising at a steady speed.

The Milky Way is one of 100 billion galaxies in the universe. Most of these galaxies are too far away for us to see without a telescope. The Andromeda galaxy, one of the Milky Way’s closet neighbors, is more than 10 billion billion miles away. When seen through a powerful telescope, the Andromeda galaxy is a beautiful swirl of flowing gas and billions of stars.

No one has ever seen the whole Milky Way through a telescope. It’s not possible to take a rocket ship to Andromeda to look back at the Milky Way. So how do we know what our galaxy looks like?

“Seeing” the Milky Way
Even without a telescope we can see that the stars have different colors: light blue, white, yellow, and orange. We can easily see that some stars are brighter than others. But to understand what our galaxy looks like, we have to know the distance from Earth to each star. That is the hard part!

To determine distance for each star, astronomers compare the stars’ positions against the back drop of distant stars and galaxies. As the Earth moves around the Sun, the stars appear to move, much as trees appear to whiz past your car window as you drive by. The closer the tree, the faster it appears to move. Using this idea, astronomers have been able to determine the distance of stars from Earth.

By carefully plotting the positions, color, and brightness of each star, astronomers discovered that a large number of older yellow stars were clustered in one place, surrounded by bands where younger blue stars are being formed. That is exactly what they saw in their telescopes when they looked at distant spiral galaxies such as Andromeda and M 100. Seen from far away, the Milky Way would look similar to these galaxies.

You may not be able to take a rocket ride into deep space, but you can see the Milky Way galaxy. All you need to do is look up at the night sky.

How the Milky Way Got Its Name
Thousands of years ago the Greeks saw a faint band of light in the night sky and thought it looked like spilled milk. So they named it the Milky Way! In fact, our modern word for a large collection of stars, galaxy, comes from gala, the Greek word for milk. We now know that this band of light is one of the spiral arms of the Milky Way, our home galaxy.