Definition · Plain-language
Milky Way
The Milky Way is the galaxy that contains the Sun, the Earth and the entire Solar System, along with hundreds of billions of other stars.
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The galaxy we live in
The Milky Way is our home galaxy — the enormous collection of stars, gas, dust and dark matter, held together by gravity, in which the Sun is just one star among hundreds of billions. Everything you can see with the naked eye in the night sky lies within it. Our Solar System sits not at the centre but well out in one of the galaxy’s spiral arms, orbiting the galactic centre over hundreds of millions of years. The Milky Way is itself one of countless galaxies in the universe, and part of a small cluster called the Local Group.
Its shape and structure
The Milky Way is a barred spiral galaxy. Most of its stars lie in a relatively flat, rotating disc, wound into spiral arms that curve out from a denser central bulge crossed by a bar-shaped concentration of stars. Surrounding the disc is a sparse, roughly spherical halo of older stars and globular clusters. At the very centre lies a supermassive black hole. Because the galaxy is shaped like a disc and we view it edge-on from within, its stars appear concentrated into a band rather than spread evenly across the sky.
Why we see a band of light
The “Milky Way” is also the name for the hazy band of light that arches across a truly dark night sky, and the two meanings are connected. Because we sit inside the galaxy’s flat disc, looking along the plane of the disc means looking through the greatest depth of stars, whose combined glow blends into a milky river of light — the origin of the name. Looking away from the plane, we see far fewer stars. Light pollution now hides this band from most people, but under dark skies it remains one of nature’s great sights.
Key facts
At a glance
- Definition: the galaxy containing the Sun and the whole Solar System
- Type: a barred spiral galaxy
- Contains: hundreds of billions of stars, plus gas, dust and dark matter
- Our place: in a spiral arm, well out from the centre
- Centre: holds a supermassive black hole
- Night sky: seen as a band of light — our edge-on view of the disc
Common misconceptions
What people often get wrong
Often heard: The Milky Way is the entire universe.
Actually: The Milky Way is just one galaxy among an estimated hundreds of billions in the observable universe. It is our home galaxy, not everything that exists.
Often heard: The Solar System sits at the centre of the Milky Way.
Actually: The Sun lies far out in one of the spiral arms, not at the centre. It takes hundreds of millions of years to orbit the galactic centre once.
Often heard: The band of light called the Milky Way is separate from the galaxy.
Actually: They are the same thing. The band is simply our view, from inside the flat disc, looking along the plane where the most stars lie and their light blends together.
Going deeper
