If you’re on a dark countryside hill some night, look up at the sky. Arcing overhead, a faint band of light may appear that looks like milk spilled across the sky. The ancient Romans called the band via lacteal, which means “milky road” or “milky way.”
The band of light that you see isn’t actually milk, of course—it’s a galaxy. A galaxy is a huge bunch of stars clustered together in space. Our solar system—which includes the sun, Earth, and seven other planets—is part of this galaxy, called … you guessed it … the Milky Way.
The Milky Way contains hundreds of billions of stars like our sun. (And like our sun, most of these stars have at least one planet orbiting them.) Earth is located about halfway between the center of the Milky Way and its outer edge.
Light at the galaxy’s center takes 25,000 light-years to travel from Earth. (A light-year is the distance light travels in one year.) So that means if you could see the core of the Milky Way, you’d be observing light that possibly left Earth before humans first settled in North America.
At the center of the Milky Way is one of the strangest and deadliest things in the universe: a black hole. Black holes are born when a giant star runs out of energy. The star implodes, causing an explosion called a supernova. The star’s heart collapses under its own weight. It’s squashed into a tiny dot you can’t see.
Scientists suspect a black hole lurks at the center of most galaxies. The Milky Way’s black hole is called Sagittarius A*. (A* is scientist-code for “A-star.”) Its gravity, or attractive force, is so strong that it pulls in anything that gets too close, including stars. So we’re lucky that Earth is located far away from the center!
DID YOU KNOW?
• All the stars and planets you can see are part of the Milky Way galaxy.
• Only one in three people in the United States can see the Milky Way band with the naked eye. Those people live far from city lights that block out stars.
• The Andromeda galaxy is the closest galaxy to the Milky Way. And it’s about two million light-years away.