Snaking across the night sky of both hemispheres, the Milky Way is the edge-on view of our
own home galaxy, one of billions of galaxies.
If you are lucky enough to view the Milky Way away from air and light pollution on a clear
night, it first appears as a faint, wispy cloud in a cloudless sky. Upon second look, you
realize you are seeing hundreds of stars—a sliver of the billions that make up our 100,000-light-year-wide galaxy. (Light travels nearly six trillion miles in one year—the
distance of a light year.) Most of the stars you can see with the naked eye are in our galaxy.
Our star, the sun, moves some 500,000 miles (804,672 kilometers) an hour around the Milky
Way, a spiral galaxy. Within the galactic disk are dense clouds of molecular hydrogen,
carbon monoxide, ammonia, water vapor, and other gases—the stuff of star formation and
perhaps even of other planets. Several places throughout the Milky Way serve as incubation
areas for stars. Observations have suggested that a massive black hole is at the center of
our galaxy in a region of gas and interstellar dust.
