Lagoon, Trifid and NGC 6559 nebulae, optical image. These nebulae lie around 5200 light years from Earth in the constellation Sagittarius. The Lagoon nebula (M8) is at lower right, the Trifid nebula (M20) at upper right, and NGC 6559 at lower left. The red regions are emission nebulae, or clouds of gas ionised by the radiation from hot young stars within them, causing them to glow. The Trifid nebula also contains regions of reflection nebulosity, where fine dust particles reflect the starlight. These regions appear blue as short- wavelength blue light is reflected more than red.