Starfield around the Sagittarius constellation showing three bright nebula: Lagoon Nebula (M8), Trifid Nebula (M20) and NGC 6559. The Lagoon nebula is at centre, the Trifid nebula at upper left, and NGC 6559 at centre 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.