Optical photograph of the Small Sagittarius Star Cloud (M24, NGC 6514), a bright patch of the Milky Way in the constellation of Sagittarius. Our galaxy, the Milky Way, has a flattened, spiral structure and contains an estimated 100 billion stars. The disc is about 99,000 light years across and the Sun lies within the Orion spiral arm at a distance of about 33,000 light years from the centre. Viewed from Earth, the Milky Way appears as a dense band of stars encircling the sky, the effect of looking out along the plane of the disc. The patchy appearance of the Milky Way is due to interstellar dust obscuring some of the more distant stars.