SaratogaSkies Jim Solomon's Astropics


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NGC 7009 (Saturn Nebula)

Image Details:

Camera: SBIG ST-2000XM
Mount: Takahashi NJP
Scope: Takahashi Mewlon 180
Configuration: Prime Focus
Additional Optics: n/a (Prime)
Filter: Astrodon LRGB I-Series Filters
Effective Focal Length: 2160mm
Effective Focal Ratio: f/12
Exposure: LRGB: 1 × 4min (binned 1×1)
Total Exposure: 0hrs, 16min
Date: 8/9/2007 11:48 PM PDT (Start)
Location: Saratoga, CA, USA
Acquisition: CCDSoft
Focus: CCDSoft
Dithering: None
Guiding: Self Guided


  • IRIS: Registration, gradient removal, Richardson-Lucy deconvolution
  • JimP: Dark subtraction, Flat field, White balance, LRGB combine, ASINH stretching
  • Photoshop: cropping, JPG conversion

Image Description:

This is NGC 7009, aka the Saturn Nebula, a planetary nebula in the constellation of Aquarius. Not only does this PN resemble the planet Saturn, but is also approximately the same apparent, angular size as the ringed planet as seen from Earth (roughly 45 arc-seconds). Deep Sky photography of such tiny targets is extermely challenging, because webcam-based techniques — such as taking thousands of very short exposures to “freeze” the atmospheric turbulence — are not possible. I'm pretty happy with this result, though, since it was really more of a test shot than anything else. I used Richardson-Lucy deconvolution in IRIS to tighten up the stars and the nebula. Surprisingly, it actually worked better (more sharpening with fewer artifacts) doing the deconvolution after contrast stretching, as opposed to running the algorithm on the linear (unstretched) image. This is an LRGB composite, with both the Luminance and color data binned 1×1. I also added the color data to the luminance exposure to create a meta-luminance before doing the LRGB combine and subsequent processing. That seemed to work better than using only the RGB data or doing the straight-forward LRGB combine. The image above is a full-resolution crop. There's nothing else in the field of interest. North is up.