The Milky Way. Optical image of the night sky, showing part of the Milky Way. The brightest part of the Milky Way is the constellation of Sagittarius (upper centre), which lies in the direction of the centre of our galaxy. The Milky Way is a luminous band in the sky caused by the light of stars which are too numerous to be seen individually. The stars are numerous because an observer looking in their direction is viewing along the plane of our galaxy's disk. The dark areas in the Milky Way are dust clouds which hide the stars behind them. The red areas at the bottom of the image are ground-based lights. Photographed over Lake Titicaca in Bolivia during June.