SaratogaSkies Jim Solomon's Astropics


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NGC 3521 (Spiral Galaxy)

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

Image Details:

Camera: Mofidied Canon Rebel XT (350D): Hutech Type I Filter Replacement
Mount: Celestron AS-GT
Scope: Celestron C8-N (8" f/5 Newtonian)
Configuration: Prime Focus
Additional Optics: Celestron/Baader Multi Purpose Coma Corrector (MPCC)
Filter: None
Effective Focal Length: 1000mm
Effective Focal Ratio: f/5
Exposure: 20 x 8min @ ISO 400
Total Exposure: 2hrs, 40min
Date: 4/19/2006 9:32:52 PM PDT (start)
Location: Saratoga, CA, USA
Acquisition: DSLRfocus
Focus: DSLRFocus
Dithering: GADFly 1.0.5
Guiding: GuideDog via Philips ToUcam Pro II (840k) through Orion ST80 w/ Celestron 2x "Kit" Barlow


  • IRIS: Dark subtraction, registration, gradient removal
  • JimP: Flat field, Kappa-Sigma Stacking, White balance, ASINH stretching
  • Photoshop: Levels, cropping, JPG conversion
  • Neat Image: Noise reduction

Image Description:

This is NGC 3521, a Spiral Galaxy in the constellation of Leo. Actually, NGC 3521 is more accurately described as a Flocculent Galaxy, due to its short, patchy, spiral arms. An interesting feature of this galaxy is the extensive halo above and below the plane of its spiral arms (ENE to WSW in the image), possibly caused by a past collision between NGC 3521 and another galaxy. The halo might be better resolved had the transparency been a bit better the night this was shot. This sky animation (1059 kB), each frame of which is one of the individual 8min exposures, shows clouds wiping out some of them, and the sky brightness affecting the others.

One of the more interesting features of this shot is that it captures the motion of a 17th-magnitude asteroid, namely, 3085 Donna, visible in the bottom-center of the full-size image (see link below) as a faint streak. This asteroid animation (645 kB) -- a small crop of that bottom-center region at full resolution -- shows the asteroid's movement from frame to frame. Thanks to Colin of the Digital Astro Yahoo Group for noticing the asteroid in my original image!

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