Milky Way galaxy. Artwork showing two views of our Milky Way galaxy, as it might be seen from a great distance. At left is an edge-on view, at right the head-on view which reveals the structure of the spiral arms. The structure of our galaxy may be inferred from detailed analysis of the distances to other stars, their relative motions and spectral characteristics. The Sun is thought to be lie on the inner edge of the Carina-Cygnus arm of the galaxy, about half way out from the centre. The milky Way has an estimated diameter of 100,000 light years and contains up to 100 billion stars.