Milky Way Galaxy

The Milky Way Galaxy is the galaxy that contains Earth, the Sun, and billions of other stars. A galaxy is a very large group of stars, gas, dust, and empty space held together by gravity. Gravity is the force that pulls objects toward each other, such as how Earth pulls people and animals downward. Because we live inside the Milky Way Galaxy, it is the part of space we can study most closely.

When viewed from a dark place at night, the Milky Way Galaxy appears as a long, milky band of light across the sky. This band is made of countless stars. They look close together, but they are actually separated by great distances. The light from these faraway stars blends together, making the band look smooth and white. This view helped ancient people name the Milky Way long before they knew it was a galaxy.

Scientists describe the shape of the Milky Way Galaxy as a spiral. A spiral is a curved shape with arms that wind around a center. The Milky Way has several spiral arms that contain stars, gas clouds, and dust. In the very middle is a bright central bulge, which is a thick area filled with many old stars. Our Solar System is not in the center but sits in a smaller spiral arm called the Orion Arm. This location is partway out from the center, closer to the galaxy’s edge.

The Milky Way Galaxy rotates, which means it spins slowly around its center. All the stars, including the Sun, move as part of this rotation. The Sun takes about 225 million years to make one full trip around the galaxy’s center. Scientists sometimes call this a "galactic year". Even though everything is moving, the galaxy stays together because gravity keeps the stars and gas from drifting away into space.

Inside the Milky Way Galaxy, new stars continue to form in clouds of gas and dust. These clouds become denser over time and may collapse under gravity to create new stars. The galaxy also contains star clusters, which are groups of stars that formed from the same cloud. At the very center of the Milky Way, scientists believe there is a black hole. A black hole is a place in space where gravity is so strong that not even light can escape. The way nearby stars move suggests that this object is extremely massive.

The Milky Way Galaxy belongs to a small group of galaxies called the Local Group. A group is a collection of things that belong together. The Local Group also includes the Andromeda Galaxy, which is the nearest large galaxy to us. Studying the Milky Way helps scientists learn how galaxies form and change and how our own Solar System fits into the larger universe.