SaratogaSkies Jim Solomon's Astropics


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NGC 7635 (Bubble Nebula)

Mouse-over to see annotations. (Requires Javascript) Click to see high-res version.

Image Details:

Camera: SBIG ST-2000XM
Mount: Astro-Physics 1200GTO
Scope: AP Starfire 160EDF APO Refractor
Configuration: Prime Focus
Additional Optics: n/a (Prime)
Filter: Astrodon SII, Hα, OIII 6nm Filters
Effective Focal Length: 1200mm
Effective Focal Ratio: f/7.5
Exposure: {8 Hα, 14 OIII, 16 SII} × 32min @ -15°C
Total Exposure: 20hrs, 16min
Date: 8/9/2008
Location: Saratoga, CA, USA
Acquisition: CCD Commander
Focus: FocusMax
Dithering: CCD Commander
Guiding: Self Guided


  • IRIS: Registration
  • JimP: Dark subtraction, Flat field, Kappa-Sigma Stacking, White balance, ASINH stretching
  • Photoshop: JPG conversion
  • CCDStack: Deconvolution

Image Description:

This is NGC 7635, aka, the “Bubble Nebula”, an emission nebula in the constellation of Cassiopeiae. This is the first tricolor narrowband image with my new AP 160 Starfire EDF refractor.

Mousing off the image reveals a “Hubble Palette” narrowband image, with R:G:B = SII:Hα:OIII. Mouse-over the image to see a pseudo-“True Color” image, in which those narrowband emission lines are mapped to their approximate color as seen by human vision. Specifically, the red SII and Hα wavelengths are mapped to red, and the aqua (blue-green) OIII wavelength is mapped to both green and blue. Also, a smidge of Hα is added into blue to simulate the Hβ wavelength.

Even after 8 hours of Sii data and 7 hours of Oiii, the image was still fairly noisy in those channels, so I replaced the luminance with the Hα image and cranked the color saturation a little. This really tamed the noise while preserving the essence of the tricolor image.

A higher resolution image is also available. North is up.