An island of stars
What Is a Galaxy?
A galaxy is a vast group of stars held together by gravity, with emptiness between each island.
-
Step 1 of 5
Stars are not spread evenly through space.
They gather into enormous groups with vast emptiness in between, rather like towns separated by hundreds of miles of open country.
-
Step 2 of 5
Gravity is what holds each island together.
Every star in a galaxy is pulled by all the others, and that shared pull keeps them orbiting a common centre rather than drifting apart.
-
Step 3 of 5
They come in a few broad shapes.
Some are flat spirals with curling arms, some are smooth featureless blobs, and some are irregular, usually after a collision.
-
Step 4 of 5
We live inside one, which makes it hard to see.
The Milky Way is our own galaxy, and because we sit within its flat disc we see it edge-on as a band of light across the sky.
-
Step 5 of 5
The distances between them are staggering.
The nearest large galaxy is so far away that its light left before humans existed, and that is our close neighbour.
Andromeda's light takes 2.5 million years to reach us, so you are seeing it as it was before modern humans existed.
The short version
A galaxy is an enormous island of stars bound by their shared gravity, separated from other galaxies by almost unimaginable emptiness.
Try it yourself
On a truly dark night look for the faint band of the Milky Way. You are looking edge-on through your own galaxy's disc.
Topics