If you are far from the city lights on a clear night, you can look up and see a broad cloudy band of white across the night sky.
This is called the Milky Way, and it is a spiral disk of more than 100 billion stars rotating clockwise once every 300 million years.
Astronomers estimate the Milky Way is about 10 billion years old and about 100,000 light years in diameter (the distance light can travel in 100,000 years). And though the Milky Way is huge, it is just one of a myriad of similar galaxies in the universe.
Our solar system is part of the Milky Way. It is about two-thirds of the distance from its center.
The first real Milky Way astronomer was Galileo. After turning his telescope on the galaxy, Galileo found that it was not a cloud, as the ancient Greeks thought, but "a mass of innumerable stars."
In the late 1700s and early 1800s, English astronomer William Hershell counted the stars in different parts of the sky and made a crude picture of the Milky Way, but he placed our solar system in the middle of the galaxy.
It was not until the 20th Century that astronomers realized the size and spiral shape of the Milky Way, and that our solar system is not near the center of the galaxy. And that is a good thing since heavy radiation near the star-packed center of the galaxy would be too strong for life.
