Trifid means split in three, and the dark lanes that do the splitting are dust sitting in front of the glowing gas. The red half emits its own light, ionised by a hot young multiple star at the centre; the blue above it is dust reflecting a separate star rather than glowing on its own. Almost everything else in this frame is hydrogen too faint for ordinary colour imaging, which is why the narrowband layer is here: it turns what looks like empty background into the cloud M20 actually sits in. The scatter of stars upper left is M21. Roughly 4,000 light-years away in Sagittarius.
