Lagoon nebula. True-colour optical image of the Lagoon nebula (M8, NGC 6523). This is a huge region of hydrogen gas and dust which glows due to ionisation of the gas by hot, young stars embedded in the nebula. It is about 30 light years across, and lies 3500 light years away in the constellation Sagittarius. Silhouetted against the glow of the nebula are several small blobs of dark dust, known as Bok globules. These dense areas of dust are thought to be star forming regions, which will eventually condense into stars. This image was produced by digitally combining photographs taken by the UK Schmidt Telescope in blue and red light.