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A galaxy is a huge group of stars held together by gravity. Each galaxy can contain up to 400 billion stars. Scientists believe there are between 100 and 200 billion galaxies. Galaxies are identified by their shape: spiral, elliptical, and irregular.
Spiral galaxies have a central disc and arms. They are bright and have many young stars. Elliptical galaxies are long oval shapes. They have older stars and are not very bright. They are the most abundant galaxy. Irregular galaxies do not have a defined shape. They have varied brightness.
The Earth's sun and its surrounding planets are found within a spiral galaxy. The galaxy is named the Milky Way. Our sun is a star on an arm of the galaxy. This means our sun is a new star and still shines brightly. The center of the Milky Way contains an enormous black hole.
Our sun revolves around the center of the Milky Way, which is moving through the universe. We are in constant motion! In the universe, the Milky Way is located near other galaxies in the local group. The Milky Way is the second largest galaxy in the local group, which also includes the Andromeda Galaxy and the Magellanic Clouds. The local group is part of a galaxy cluster called the Virgo supercluster.
Galaxies seem to be everywhere, but much of the universe is empty space. Even though scientists estimate that there are billions and maybe even trillions of galaxies, they only make up five percent of the universe.
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