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NGC 6822 (Barnard's Galaxy)

[Hα+R G B]

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: Hutech Hα Front Filter (HA-FF)
Effective Focal Length: 1000mm
Effective Focal Ratio: f/5
Exposure: 83 x 4min @ ISO 1600 (RGB), 22 x 8min @ ISO 1600 (Hα)
Total Exposure: 8hrs, 28min
Date: 8/23/2006 and 8/24/2006 (RGB); 8/27/2006 (Hα)
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

Processing:

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

Image Description:

This is NGC 6822, aka Barnard's Galaxy, an irregular (as opposed to spiral or elliptical) galaxy in the constellation of Sagittarius. NGC 6822, a member of the Local Group, is a relatively close neighbor of our own Milky Way galaxy, along with M31 (Andromeda) and others.

This image was collected over three nights: two very dewy nights worth of RGB exposures, and a third night of Hα exposures. The Hα exposures really helped to bring out the star-formation regions at the top (North) of NGC 6822. Yes, that's correct, those emission nebulae are in NGC 6822, not in our own Milky Way!

Mousing-over the image will show the Hubble designations of those regions, and will switch the displayed image to the processed Hα-only image, shown in grayscale (which, trust me, is easier on the eyes than a redscale image). One of these regions, IC 1308 (aka “[H25] X” or “Hubble X”), is rougly 11 times the size of M42 in our own Milky Way.

This image is a do-over of this this old version. (By the way, I have no idea why that old version came out so green—the color in the current version is likely to be far more accurate.) A higher-resolution image is also available. North is up.