... Although auroras might first appear to be moonlit clouds, they only add light to the sky and do not block background stars from view. Our Galaxy in Stars, Gas, and Dust . ... The red nebulae visible in the above contrast-enhanced picture are primarily emission nebulae, glowing clouds of hydrogen gas heated by nearby, bright, young stars. ... Next stop: Mars. ... A closer look of the Eagle Nebula, however, shows the bright region is actually a window into the center of a larger dark shell of dust. ...