The Dark Shark (LDN 1235) scavenges The Rotten Fish (LDN 1251).

This strange pelagic dustscape swims high above our northern autumn skies and is really and truly not what it appears!

At top left a dead fish appears to decay and disintegrate, dripping tendrils of rot deeper into the water. At bottom right a lurking shark smells opportunity and lunges upward to grab what’s left. This story of aquatic scavenging is in fact a remarkable example of pareidolia, the human tendency to see familiar patterns in random unrelated visual data.

In fact the image really shows huge clouds of thick interstellar dust that clogs the plane of our Milky Way galaxy. The fishy dust clouds shown here span about 30 light years across and are located about 650 light years away in the direction of the circumpolar constellation named for Cepheus the Rasta-King of Aethiopia in ancient Greek legend.

Centuries ago, astronomers realized that some kind of absorbent material obscured the stars in the direction of the galactic disk. They called this mysterious stuff “dust” and both the dimming and reddening of starlight by thick clouds of it has been known since at least the early 1800s.

We now know this stuff to be microscopic grains of minerals coated with mantles of organic ice made of frozen water, CO2, CO, methane, ammonia, and more complex molecules. Dust is very good at absorbing and scattering starlight. At the same time the clouds are almost perfectly transparent to the longer waves of thermal infrared.

This selective transparency produces a reverse greenhouse effect which allows thick molecular clouds to shade their interiors from high-energy photons while efficiently cooling themselves off via thermal emission. The resulting cryogenic temperatures (just a few dozen degrees above absolute zero) allow complex organic reactions to assemble an amazing suite of prebiotic compounds including sugars, alcohols, amino acids, nucleic acids, and even complete proteins. The galactic disk is in fact filthy with frozen organic sludge!

These dust clouds are so ridiculously dark that it’s nearly impossible to take images like this from light-polluted suburbia because the air itself glows more brightly than the starlight reflected by the dust. Instead dust must be imaged from extremely dark skies.

This image is certainly not my best, but represents an effort years in the making to get equipment working properly at a remote dark site in the high mountains (10,500 feet = 3200 m elevation) with thin air, frozen fingers, and no electricity. I’m not sure whether it was the cold or my mushy brain that made it so hard, but I’ve been trying to shoot these targets for longer than I care to admit!

This is 7.5 hours of exposure with a 5-inch diameter refractor (447 x 60s color exposures at a focal length of 488 mm). I shot the sub-frames on two nights Sep 3-4-5 but screwed up the flat-frames and had to make another trip up to the high country last weekend to redo them.