The Dark Clouds of Cygnus
Stare into the starfields of Cygnus and ponder what lies undiscovered in our part of the Milky Way.
You are looking down the spiral arm we live in, into clouds of stars seemingly packed together. Every one of those specks is a sun like ours. With planets? Very likely, as we now know.
Amid the stars float glowing red clouds of hydrogen gas. The North America Nebula shines at lower right.
Snaking northward from the “arctic” region of the bright nebula is a river of dust that broadens into a delta of dark nebulosity. Once thought to be holes in the sky allowing us to see deeper into space, we know now that these dark nebulas are really foreground dust clouds filled with the soot of dying stars, carbon dust that absorbs starlight and obscures the more distant parts of the Milky Way.
This dust cloud is called Le Gentil 3, named for the 18th century French astronomer who first noted its position in the sky. Le Gentil’s dust cloud is one of the easiest features of the summer Milky Way to see. Look north of Deneb, the bright star at the right of the image, and with the unaided eye on a dark moonless night you’ll see what looks like a dark hole in the Milky Way. That’s Le Gentil 3.
I use this dust cloud as a measure of sky brightness. On a truly dark night, Le Gentil 3 looks darker than any other area of sky, even relatively starless regions off the Milky Way. Most of the sky brightness we see from a dark site is really starlight. But Le Gentil’s proximity and opaqueness makes it appear darker than the more distant starlit sky background.
This image covers about the width of a binocular field. I shot it from the Cypress Hills in Saskatchewan this past weekend, using the Canon 5D MkII at ISO 1600 and Canon 135mm telephoto lens at f/2.8. It’s a stack of 10 five-minute exposures.
— Alan, August 22, 2012 / © 2012 Alan Dyer