Along with summer come the Milky Way star fields of The Summer Triangle and Sagittarius. The constellation of Cygnus is home to a large complex of emission nebulae. The most famous of these is the The North American Nebula, NGC-7000.

Well, I didn't shoot that one.

The North American complex is a little big for my sensor/scope combination, so I went for the lesser well-known Crescent Nebula, NGC-6888. This image is the result of one hour's worth of five minute exposures through a Baader 7nm Hydrogen Alpha filter.

Emission Nebulae like this, well, emit strongly in a wavelength of light (Hydrogen Alpha) which is very easy to isolate with a specialized filter. Happily, this wavelength also falls outside of the portion of the visible light spectrum where light pollution resides. This allows images taken through a h-Alpha filter to be acquired from within light polluted areas. So, I can set up in my driveway where I can barely see magnitude 4 stars and shoot long exposures of dim objects.

Click the thumbnail below to view a larger version:

NGC-7000, Crescent Nebula in Cygnus
Astro-Tech AT106LE, 106mm f/6.5 triplet
Astro-Tech Field Flattener
SBIG ST8300M w/FW5-8300
Baader 7nm Hydrogen Alpha
Guided w/ Oriion ST80 & Starshoot Autoguider
Celestron CGE Mount
Lights: 12 X 5min exposures @ -5C
50 Darks
No Flats
Stacked in Deep Sky Stacker
Processed with Photoshop CS4