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The Hole in the Trees Skybox | all galleries >> Deep Sky >> Planetary Nebulae > Abell 21
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Abell 21

The Medusa Nebula in Gemini

Optics/Mount: CPC1100 with f6.3 Celestron reducer on a Milburn Wedge. Dec antibacklash set to 27/27. PEC on.

Luminance Data:
Camera: DSI II Pro
Exposure: 57 x 4 minutes = 3hrs 48 minutes
Date: January 15-16 and January 18-19, 2012
Conditions: Seeing 2-3/5 (3.1-3.8 arcsecs). Transparency 3/5. No wind. Temp 19-22 F.
Image scale at capture: 1.06 arcsecs/pixel = f/5.9
Guiding Hardware: Flea 3, Taurus Tracker III off axis guider. Guiding scale 0.71 arcsec/pixel. 1 second guide exposures.
Guiding Software: PHD. Aggressiveness 100, Hysteresis 0, Minimum Move 0.9, Max RA 1000, Max Dec 600. Dec set to auto/resist switching. Dithering set to Extreme with Settle < 0.5. Calibration steps 7 x 10.
Guiding performance: FWHM of subs = 4 arc seconds. RMS 0.53 arc seconds, OSC 0.31.

Color Data:
Camera: QHY8
Exposure: 17 x 10 minutes
Date: February 17-18, 2012
Conditions: Seeing 2/5 (3.2 arcsecs). Transparency 3/5. Occasional breezes. Temp 40 F.
Image scale at capture: 0.94 arcsec/pixel = f/6.1
Guiding Hardware: DSI II Pro, Taurus Tracker III off axis guider. Guiding scale 1.02 arcsec/pixel.
Guiding Software: PHD. Guide star mag 9.96. Aggressiveness 100, Hysteresis 0, Minimum Move 0.6, Max RA 1000, Max Dec 600. Dec set to auto/resist switching. Dithering set to Extreme with Settle < 0.5. Calibration steps 7 x 9.
Guiding performance: FWHM of subs = 4.75 arc seconds. RMS 0.57 arcsecs.

Light pollution: Bortle 8 (white zone)
Filters: Astronomik 2c L for luminance frames, Orion Skyglow Imaging filter for RGB frames.
Scale of presentation: 1.88 arcsecs/pixel (50%); frame cropped
Capture software: Sequence Generator 2 and Nebulosity 2. Monitored remotely with TeamViewer.
Processing: Stacked with Deep Sky Stacker, post-processed with Photoshop CS2.


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