Milky Way

The Milky Way is the galaxy that Earth lives in. A galaxy is a huge group of stars, gas, dust, and planets, all held together by gravity. The Milky Way holds our Sun and at least 100 billion other stars. From Earth, it looks like a pale, milky stripe across a dark night sky. That is where the name comes from.

The Milky Way is shaped like a flat disk with a bulge in the middle. Long curved arms wrap around the bulge, made of bright stars and clouds of gas. Our Sun sits on one of these arms, called the Orion Arm. The Sun is not near the center. It is about halfway out from the middle, in a quieter part of the galaxy.

The size of the Milky Way is hard to picture. Light is the fastest thing in the universe, and it still takes about 100,000 years for light to cross from one side of the galaxy to the other. That distance is called 100,000 light-years. Our whole solar system, from the Sun to Pluto, would be a tiny dot on a map of the Milky Way.

Everything in the galaxy is moving. The Sun, Earth, and all the other stars slowly orbit the center of the Milky Way, just like planets orbit the Sun. The Sun travels at about 500,000 miles per hour. Even at that speed, it takes around 230 million years to go around the galaxy just once. The last time the Sun was in this same spot, dinosaurs were just starting to appear on Earth.

At the very center of the Milky Way is a giant black hole called Sagittarius A star. It has as much mass as about four million Suns squeezed into a small space. Scientists took the first real picture of it in 2022, using a group of telescopes spread all over Earth. What happens inside a black hole is one of the biggest open questions in science. Nobody knows yet.

The Milky Way is not alone. It belongs to a small group of galaxies called the Local Group. Its biggest neighbor is the Andromeda galaxy, which looks a lot like the Milky Way but is even larger. Andromeda is moving toward us. In about 4.5 billion years, the two galaxies will crash and slowly blend into one big galaxy.

The next time you look up at a dark country sky and see that pale band of light, you are looking at the galaxy from the inside.