The Eagle Nebula is a region of our galaxy where stars are currently
forming out of dusty hydrogen gas. Ultraviolet light from newly-formed
stars in the vicinity of the nebula is pumping energy into these
gas clouds, causing them to glow in visible light.
The final image depicts red light from hydrogen atoms as green,
red light from sulfur ions (sulfur atoms with one electron removed)
as red, and green light from doubly-ionized oxygen (oxygen atoms
with two electrons missing) as blue.
These color reassignments enhance the level of detail visible
in the image, because otherwise the red light from hydrogen and
that from sulfur would be hard to tell apart.
In the final image, the blue-green haze indicates light from
hydrogen and oxygen surrounding the dark columns. The columns
display reddish highlights identifying light from sulfur.