Two types of gas meet, and have a party….

 

The triffid nebula, or Messier 20, is a lovely southern nebula visible in the summer, which contains both an emission nebula (red) and a reflection nebula (blue).  It gets its name from the three-way partition of the red area by the dark dust lanes.

For the photographically inclined, this is F/6, and the FL=1200mm.