Large Sagittarius Star Cloud
Really big congregations of star clusters that have lost their individual structure and mixed with each other, are known as star clouds. The Large Sagittarius Star Cloud is one of these regions often described as that steam coming out the constellation Sagittarius’s “teapot’s spout”. According to the ancient Greeks, Sagittarius depicts a centaur. But once a green laser wielding Dark Ranger has connected the dots to trace out a teapot, you’ll be hard pressed to visualize that pattern of stars any other way again. The star cloud itself is often referred as “the brightest section of the Milky Way.” That’s in part because all these stars are yellow and orange giant stars. While the star cloud is the first subject to catch your eye in this enigmatic scene, that is not the interesting structure captured in the piece of astrophotography.
This mosaic of five images also shows a close-up view of a small section the ribbon of darkness that runs throughout the middle of the Milky Way. It was originally misnamed as "the Great Rift" by astronomers of the 1800s (to this day astronomers continue to be terrible at naming things). Instead of being empty space, it's actually full space where the equilibrium between gravity and the galaxy's rotation, congregates dust and gas onto the galaxy’s plane of rotation. “Full space” is a misleading descriptor. While these regions can adsorb all the starlight in the optical wavelengths that tries to pass through them, it is not because of they are truly dense, but instead because they are enormous. We think of the air we breathe of being transparent yet it contains an astonishing 10 quintillion (19 zeros) molecules per cubic centimeter. In the other extreme, the densest of Milky Way’s dark regions only have a density 100,000 molecules / cm3. If our atmosphere was also 100s of light years thick, instead of merely a few 100 miles, it would be 13-orders of magnitude more opaque. Keep in mind the density difference between air and gold is only 6 orders of magnitude.
In the 1950s astronomers renamed these regions of galactic darkness “molecular clouds” which is technically more accurate but means nearly nothing since all clouds in Universe, not to mention all matter made when two or more atoms form a chemical bond are by definition molecules. Dark Rangers, who are better at correcting astronomer's misnomers, call these clouds of compressed dust and gas "Lumpy Darkness" as might anybody asked to describe this art.
The Milky Way is not the only galaxy that contains the vast dark lanes. For instance, the Andromeda Galaxy appears to be a featureless glow, earning the reputation for being one of the most disappointing objects you can see through a telescope because it looks nothing like what you would expect after having seen it via astrophotography. But if your sky is dark enough and your telescope is big enough, you can see thin arcs of darkness almost like parenthesis bracketing the galaxies core – those are Andromeda’s skinny ribbons of lumpy darkness. And once you recognize them for what they are, suddenly Andromeda start to look like something.
The Cigar Galaxy, with its edge on orientation, has very thick knots of the same darkness, indeed as thick as that galaxy’s rather plump disc is tall. Since lumpy darkness is the source material for bringing new stars into existence, it can be inferred that the Cigar Galaxy has billions of unborn stars in its reserves, far more then even big mama Andromeda.
Where good views of the Milky Way are still possible, you don't need astrophotography or even a telescope to recognize the difference in texture and hues of darkness when you compare the deep black lumpy darkness of the galaxy's plane to the smooth dark-grey of empty space. When these lumps of darkness are further contracted by the mutual gravity of their particles they can become star-birth nebulae. The pink and blue clouds in the upper left corner of this image are examples of these star forming regions, known as the Lagoon and Trifid Star-birth Nebulae.
If you hang this masterpiece of magnified Milky Way astrophotography on your wall it’s likely to mistaken for abstract art. Now you have to decide if it easier to play along with that misconception or try to explain to them what they are really looking at.
