Animation of a flight out from the centre through the arms of the Milky Way galaxy, looking backwards. The Milky Way is the galaxy that contains our solar system. It is thought to be a barred spiral galaxy some 120, 000 light years in diameter, containing as many as 400 billion stars. The inner bulge contains mostly older, redder stars, while the flat spiral arms contain more younger, bluer stars. The Milky Way is one of billions of galaxies in the universe.