Wonders in the Sky Dark Nebula Le Gentil 3 Back | Up | Next

Piggy-Back, Filtered, Stacked
Dark Nebula Le Gentil 3

Now we are beginning to combine all of the tricks in our astrophotography arsenal.

To record the red hydrogen-alpha light, longer exposures through a filter were used.

Reasonably dark skies also helped tremendously. The Milky Way was visible from this site, even though it had a lot of light pollution in the west. This field was shot in the northeast, before it transited the meridian.

Finally, stacking multiple exposures also helped greatly increase the signal-to-noise ratio and make faint details and contrast between the dark nebulas and sky more visible.

Le Gentil 3 is a large dark nebula between Cygnus and Cepheus.

Its shadowy filaments fill the area of sky in the upper center of the frame between Deneb and the North America Nebula in Cygnus at upper right and Herschel's Garnet Star and IC 1396 in Cepheus at left.

Le Gentil 3 is named after the French observer Guillaume-Joseph-Hyacinthe-Jean-Baptiste Le Gentil de la Galaziere, who observed and cataloged it in the 1700s. It is also known as Globular Filament 7 (GF 7).

The red nebulas in the image glow from the light of ionized hydrogen gas. Dark nebula are concentrations of obscuring dust and dark matter in space that are opaque that don't let the stars behind them shine through.

Le Gentil 3 is easily visible to the unaided eye from a dark-sky observing site. Numerous other smaller dark nebulas are also scattered across the field, most listed in E. E. Barnard's famous catalog of dark nebulas.

This photo is a stack of six 155-second sub exposures for a total of 15.5 minutes of exposure.

Image Data

  • Lens / Scope: Nikon 50mm f/1.4 manual focus lens with Fotodiox Canon adapter
  • Focal Length: 50mm
  • F/stop: f/2.8
  • Exposure: Stack of six 2.5-minute exposures (15.5 minutes total exposure)
  • Mount: Orion Sirius polar-aligned German-equatorial mount
  • Guiding: None
  • Camera: Unmodified Canon EOS 1000D (Digital Rebel XS)
  • Mode: JPEG
  • ISO: 1600
  • White Balance: Custom, set on sky background
  • In-Camera Noise Reduction: Off
  • Filter: IDAS LPS Filter
  • Temp: 56F
  • Start Time: 3:34 a.m.
  • Date: June 1, 2009
  • Location: Maxwell, NJ
  • Calibration: None
  • Processing: Standard in-camera JPEG processing. Stacked in Deepsky Stacker. Contrast and color adjusted in post processing.



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