The stars in our immediate neighbourhood, including most of those which can be visible to us, are about equally dense in all directions. A careful statistical study of star motions makes it very probable that the stars in our neighbourhood, including the sun, are moving round the centre of the Milky Way, which is in the constellation Sagittarius, probably in spiral rather than elliptical orbits. The whole system of all the stars is a biscuit shaped object about five thousand parsecs thick, and perhaps thirty thousand across. With a good telescope it is seen to consist of stars arranged in a rather irregular spiral. Among the brighter stars in it are some Cepheid variables, so its distance can be measured, and consequently its actual size. The telescope shows that the light from them is reddened, not by a scattering of the blue light but by lowering of the frequencies of vibration of light of all kinds.