We can think of our location in the universe along the lines of an address. The street would be planet Earth, the county would be the solar system, and the country would be the Milky Way Galaxy. The state would be the Orion Arm – a ribbon of stars that wraps part of the way around the galaxy.

The Milky Way is a disk that’s about a hundred thousand light-years wide. It has a long “bar” of stars in its middle. Spiral arms extend from the ends of the bar and wrap all the way around the galaxy. They make the Milky Way look like a pinwheel spinning through the void.

The arms don’t contain more stars than the darker regions between them. Instead, the arms are like waves on the ocean. As a wave washes through the galaxy, it squeezes clouds of gas and dust, giving birth to new stars. Many of those stars are big, hot, and bright. So they make the spiral arms look bright and blue. But such stars die quickly, so the wave of brightening doesn’t last.

A few shorter arms fill in between the major ones. And the Orion Arm fits into that category. It’s about 3500 light-years wide and 20,000 light-years long. At our distance from the center of the Milky Way, the arm wraps only about a quarter of the way around the galaxy.

The arm is named for Orion because of the arm’s location in the sky. The stars of Orion are among its most prominent members. But the arm includes almost all of the stars that are visible to the unaided eye.

Script by Damond Benningfield