This beautiful photo is of the Rho Ophiuchi cloud complex, one of the most colorful and active star-forming regions in the visible universe.
Somewhat contrary to the original post's caption, this isn't a single nebula but rather a group of nebulae. This particular photo captures Lynds 1688; the largest and most active section of the complex. It's a dark nebula, meaning it doesn't emit or reflect visible light like other nebulae. It's body is so dense that it blocks light from stars and other objects behind it, causing it to appear a "dark" nonvisible void. (The original captioning may be misleading as the complex is made up of multiple nebula including those that reflect or emit visible light).
Now you may be thinking, if it's a dark nebula, why is this picture so colorful and detailed? It very clearly shows the formation and discernable details, not very obscured or dark at all.
This is because of false coloring.
Because dark nebulae block/absorb visible light, astronomers use telescopes that capture different wavelengths of light that give us a clearer picture. In particular, I recognize this image from NASA's WISE telescope, WISE standing for Wide-field Infrared Survey Explorer, a telescope that specially took infrared pictures.
The colors present are due to false coloring, which as I mentioned in my last post is a common technique in astrophotography that's useful for several reasons. Here, it allows us to perceive and visualize lengths of light that are not visible to the human eye.
In this image, blue and cyan coloring represents light of wavelengths 3.4-4.6 microns, mainly emitted by stars. Green and red represent wavelengths 12-22 microns, that mainly come from the dust of the nebula itself.
Sources: WISE Unveils a Treasure Trove of Beauty & Dark Nebula Swinburne University
image: NASA/JPL-Caltech/WISE Team
