The Trifid Nebula (M20) and the Lagoon Nebula (M8) against the backdrop of the summer Milky Way Galaxy. The Trifid is a combination of an emission nebula, the reddish glow, a dark nebula, the dark areas in the nebula and a reflection nebula, the blueish area. The red emission is caused by hot massive stars in the nebula ionizing the surrounding cloud causing it to glow. The dark areas are thicker concentrations of the nebula that block light from behind it. The blue parts is caused by light from the hot massive blueish stars reflecting off of the dust grains.
The Lagoon nebula is primary an emission nebula but it has thicker concentrations of material in it. The small dark ones are referred to as Bok globules which are collapsing areas of the nebula. Both nebulae contain new and protostars forming out of the surrounding regions.